,transcriber's ,notes3 ,variations in   
spelling and hyphenation have been left 
as in the original4 ,words in italics in
 the original are surrounded by         
underscores4 ,words in bold in the      
original are surrounded by equal signs4 
,ellipses match the original4  ,a few   
typographical errors have been          
corrected4 ,a complete list as well as  
other notes follows the text4           
,,disease ,,in ,,plants                 
,,disease ,,in ,,plants                 
,,by                      ,h4 ,,marshall
 ,,ward1 ,sc4,d41 ,f4,r4,s4    ,,fellow 
,,of ,,sidney ,,sussex ,,college1       
,,honorary ,,fellow ,,of ,,christ',s    
,,college          ,,and ,,professor    
,,of ,,botany ,,in ,,the ,,university   
,,of ,,cambridge      ,,president ,,of  
,,the ,,british ,,mycological ,,society1
 ,,and ,,fellow ,,of ,,the              
,,linnean ,,and ,,royal ,,horticultural 
,,societies2 ,,honorary ,,fellow        
,,of ,,the ,,manchester ,,literary ,,and
 ,,philosophical ,,society              

,,and ,,of ,,the ,,botanical ,,society  
,,of ,,edinburgh                        
,london                                 
,,macmillan ,,and ,,co41 ,,limited      
,,new ,,york3 ,,the ,,macmillan         
,,company                               
#aija                           ,all    
rights ,reserved                        
,,glasgow3 ,,printed ,,at ,,the         
,,university ,,press                    
,,by ,,robert ,,maclehose ,,and ,,co4   
,,preface4   ,it has often been         
represented to me that the cultivators  
of plants1 among whom are to be included
 planters and foresters1 as well as     
agriculturists and gardeners of every   
kind1 are more particularly concerned   
with1 and interested in1 the maladies   
themselves of the plants they grow1 than
 in the life-history of the fungi1      
insects or other organisms to which they
 are due1 or in the physiological       
processes which are involved2 and       
although it is impossible to really     
understand any disease unless we also   

understand the processes by which it is 
brought about1 there is room for        
sympathy with the point of view of the  
cultivator4 ,he says1 in effect1 ,i do  
not want to know all about the biology  
of the fungus of wheat-rust1 or of the  
phylloxera1 nor do ,i want to learn what
 experts can tell me about the action of
 bacteria in soil1 or the process of    
starch-formation in the leaves3 ,i have 
neither the time nor the means to master
 these details4 ,what ,i want is        
guidance as to what is wrong with my    
tomatoes1 apple trees1 chrysanthemums1  
fir trees1 turnips1 etc41 and what ,i am
 to do to set things right4 ,just so4   
,with the latter part of this cry one   
must sympathize1 much as a doctor does  
with the wail of the parent who calls   
him in to cure his sick child--we need  
not stop to classify or compare the     
motives of the parent and the           
cultivator1 and perhaps ,i had done     
better to select a breeder of sheep with
 his flock and a veterinary doctor in   

the illustration1 but we will let it    
pass2 and as regards the former part of 
the cry1 ,i do not know that the        
plant-doctor can expect the cultivator  
to be initiated in the aetiology of the 
disease any more than the physician     
expects the parent to understand the    
biology of the typhoid bacillus4 ,that  
both the cultivator and the parent would
 be the better for a real knowledge of  
the disease in either case must be      
admitted--nay insisted on1 provided the 
knowledge is real--but we have to deal  
with facts1 and it is a fact that the   
clients of both doctors are impatient of
 the details of the case4  ,now1 of     
course1 ,i am aware that no short cut or
 royal road to science exists1 and if a 
man is going to train up trees or other 
plants1 he ought to know all about them 
in health and in sickness1 in youth and 
in old age1 and he ought to learn       
everything about the soil they grow in1 
the air that surrounds them1 the enemies
 that beset them1 and all the           

multifarious relations of these one to  
another2 but when ,i look at my boy and 
reflect how much his nurse1 his         
schoolmaster1 his tutor1 his doctor1 and
 his parents ought to know successively 
and simultaneously about him in sickness
 and in health1 and about his           
surroundings1 etc41 ,i begin to wonder  
whether there is not after all something
 to be said for the cultivator's point  
of view4  ,moreover1 the cultivator     
knows a good deal about his plants which
 ,i do not know1 and although ,i should 
much like to know it1 his plea of want  
of time rings in my ears and the        
conviction strikes home that one ought  
to try and meet his views1 and tell him 
something about disease as manifested in
 plants without insisting on his        
becoming a professional mycologist1     
entomologist1 agricultural chemist1 and 
philosopher4  ,of course1 beyond a      
certain point1 it is his lookout how    
much the information is worth1 and its  
educational value--a very different     

matter--is sure to suffer from any      
restrictions imposed on the treatment of
 the subject2 but if the theme of       
disease in plants1 treated from a       
general point of view--,i was about to  
write treated in a popular manner1 but  
that is impossible until physiology and 
mycology are more widely taught--enables
 him to understand better the questions 
he puts to himself1 and1 still more1 if 
it stimulates him to enquire further    
into the inexhaustible field of science 
glimpsed at1 something may come of it4  
,the purpose of these essays is to treat
 the subject of disease in plants with  
special reference to the patient itself1
 and to describe the symptoms it        
exhibits and the course of the malady1  
with only such references to the agents 
which induce or cause disease as are    
necessary to an intelligent             
understanding of the subject1 and of the
 kind of treatment called for4          
,consequently ,i have avoided any       
unnecessary classification or elaborate 

descriptions of parasitic fungi or      
insects1 histological details of the    
tissues of plants1 chemical and physical
 details regarding the soil1 and even   
matters purely physiological as far as  
possible4 ,several admirable works on   
these subjects are already available1   
and must be referred to for further     
details4  ,it is1 however1 quite out of 
the question to avoid technicalities1   
though ,i have chosen the simpler course
 wherever it was found feasible1 and    
have tried to so employ the examples    
selected that the student who wishes to 
go further into the matters dealt with  
may turn to special treatises for       
further information4 ,for one eminently 
technical section ,i ought perhaps to   
apologise1 but the temptation to try and
 set forth1 in concrete form and        
suitable for the purposes of this book1 
some account of what is known of the    
most essential and profound factors     
concerned in the difficult question of  
the nature of life and death1 health and

 disease1 was great4 ,probably my       
apology should go further1 and apply to 
what after all must be failure to       
explore this mystery to the bottom3 my  
only excuse must be that it may         
stimulate others to go further4  ,it was
 an afterthought to add1 in ,part ,i41  
the considerations on the factors which 
influence the plant regarded as a living
 machine1 so to speak1 in order that the
 student may the better apprehend the   
point of view taken of the bearings of  
the matters discussed in ,part ,,ii4    
,with regard to references1 it seemed a 
better plan to give1 in the form of     
notes after each chapter1 the titles of 
the principal books and papers on which 
a student may base a further course of  
reading1 than to overweight the pages of
 what is1 after all1 merely an          
introductory sketch to a huge subject1  
with detailed quotations from the       
numerous sources of information made use
 of4 ,i have freely expressed my own    
opinions1 but the sources for others    

are1 ,i hope1 as freely given4 ,it will1
 however1 be understood that ,i have not
 aimed at a complete bibliography1 and1 
particularly1 ,i have only given foreign
 references where it seemed that        
adequate treatment of the subject could 
not be found in ,english4  ,my sincere  
thanks are due to ,mr4 ,f4 ,darwin1     
,f4,r4,s41 who has kindly looked through
 many of the proofs1 and given me the   
benefit of several suggestions3 and to  
my wife for the very material aid she   
has afforded me in the preparation of   
the index4                              
,h4 ,,marshall ,,ward4                  
,,cambridge1        ,november1 #aijj4   
,,contents4     ,,part ,i4--,,some      
,,factors4     ,,chapter ,i4            
,,page   ,,the ,,plant ,,and ,,its      
,,surroundings1                      #a 
,,chapter ,,ii4    ,,the ,,plant ,,and  
,,its ,,food1                           
#g     ,,chapter ,,iii4    ,,the ,,plant
 ,a ,,living ,,machine1                 
#ae     ,,chapter ,,iv4    ,,metabolism1

                                        
#bc     ,,chapter ,v4    ,,roots ,,and  
,,root-,,hairs1                         
#ce     ,,chapter ,,vi4    ,,the        
,,functions ,,of ,,root-,,hairs1        
#de     ,,chapter ,,vii4    ,,the       
,,biology ,,of ,,soil1                  
#ef     ,,chapter ,,viii4               
,,hybridisation ,,and ,,selection1      
#fi     ,,part ,,ii4--,,disease ,,in    
,,plants4     ,,chapter ,,ix4           
,,phytopathology4 ,,derivation ,,and    
,,meaning1             #he     ,,chapter
 ,x4    ,,health ,,and ,,disease1       
#ia     ,,chapter ,,xi4    ,,causes ,,of
 ,,disease1                             
#ii     ,,chapter ,,xii4    ,,causes    
,,of ,,disease4 ,,the ,,living          
,,environment1         #ajh             
,,chapter ,,xiii4    ,,nature ,,of      
,,disease1                              
#aai     ,,chapter ,,xiv4    ,,nature   
,,of ,,disease 7,continued71            
#acj     ,,chapter ,,xv4    ,,spreading 
,,of ,,disease ,,and ,,epidemics1       

#adb     ,,chapter ,,xvi4    ,,the      
,,factors ,,of ,,an ,,epidemic1         
#adi     ,,chapter ,,xvii4    ,,remedial
 ,,measures1                            
#aei     ,,chapter ,,xviii4             
,,variation ,,and ,,disease1            
#afh     ,,chapter ,,xix4    ,,symptoms 
,,of ,,disease1                         
#agi     ,,chapter ,,xx4    ,,symptoms  
,,of ,,disease 7,continued71            
#ahf     ,,chapter ,,xxi4               
,,artificial ,,wounds1                  
#aid     ,,chapter ,,xxii4    ,,natural 
,,wounds1                               
#bjd     ,,chapter ,,xxiii4             
,,excrescences1                         
#bab     ,,chapter ,,xxiv4              
,,excrescences 7,continued71            
#bbb     ,,chapter ,,xxv4               
,,exudations ,,and ,,rotting1           
#bbg     ,,chapter ,,xxvi4    ,,necrotic
 ,,diseases1                            
#bdj     ,,chapter ,,xxvii4             
,,monstrosities ,,and ,,malformations1  
#bdf     ,,chapter ,,xxviii4            

,,proliferations1                       
#beg     ,,chapter ,,xxix4    ,,grafts1 
#bfb     ,,chapter ,,xxx4    ,,life     
,,and ,,death1                          
#bga     ,,index1                       
#bic     ,,part ,i4  ,,some ,,factors4  
,,chapter ,i4  ,,the ,,plant ,,and ,,its
 ,,surroundings4       ,the plant the   
central object of study--soil1 climate1 
atmosphere1 etc41 are factors of its    
environment4 ,agricultural              
chemistry4 ,the plant a machine4        
,physiology4   ,if ,i were asked to sum 
up the most important result of the     
numerous advances made during the past  
decade in agriculture and forestry1 ,i  
should reply--the clearer and wider     
recognition of the fact that the plant  
itself is the centre of the subject1 and
 not the soil1 climate1 season1 or other
 factors of its environment4 ,until     
comparatively recent times it was the   
habit of farmers1 foresters1 planters1  
and gardeners1 all the world over1 to   
look upon the plant as a mere item or as

 a mysterious if important one in their 
calculations1 and to regard the soil as 
the chief factor in their studies4  ,now
 all is changing1 and the world is      
gradually awakening more and more to the
 recognition of the truth that the soil 
and the clouds and the atmosphere are   
merely reservoirs of more or less inert 
materials1 from which the living plant  
draws its supplies1 and works them up1  
by means of energy focussed from the    
sun1 into new plant substance4  ,in     
other words1 the more far-seeing        
pioneers of scientific agriculture and  
forestry1 etc41 are recognising that    
agricultural chemistry is not the be-all
 and end-all of agricultural science2   
but that1 in place of the study of the  
chemical analyses of dead soil1 water1  
air1 and plant-remains1 which has so    
long held sway1 largely owing1 ,i think1
 to the influence of ,liebig1 the       
student should have his attention more  
concentrated on the living plant itself 
and on the physiological actions which  

make up its life4 ,he must regard the   
living plant as a sort of working       
machine--infinitely more complex than   
any machine made by man1 but a machine  
nevertheless--the purpose of which is to
 store up energy from the sun1 and so to
 add to our wealth on this planet1 at   
the expense of the extra-terrestrial    
universe4  ,it is not1 be it noted1 that
 the new study proposes to ignore or    
abandon the old studies3 modern         
physiology owes too much to the physics 
and chemistry on which it is partly     
based1 and to the labours of ,de        
,saussure1 ,ingenhousz1 ,priestley1 and 
others1 for that4 ,but it is that the   
new study recognises that the central   
point1 to which all views must be       
focussed1 is not the one that it was    
formerly supposed to be4 ,the student is
 still taught that the chemistry of     
soils yields valuable information1 and  
that lessons of importance are derived  
from comparisons of the analyses of the 
ashes1 etc41 of plants2 but he is no    

longer able to cherish the hope1 however
 remotely1 that such studies solve his  
most important problems4  ,the scene--or
 rather the point to which attention is 
now directed--is the living1 working1   
energy-accumulating plant itself1 and   
not the dead store of materials in the  
soil4 ,the reason for the change is not 
far to seek3 it is due to the enormous  
strides made in the study of the        
physiology of plants during the last    
quarter of a century1 and the subject   
abounds in examples illustrating the    
marvellous advances that have been made1
 and at the same time showing how1 in   
the progress of researches1 made for    
their own sake--i4e4 in pursuit of      
satisfaction for the intense curiosity  
of the scientific man--all kinds of side
 issues turn up which prove to be of    
value in practice1 and suggestive of    
further thinking4  ,at the beginning of 
the nineteenth century--i4e4 about      
#ahbj--the best thinkers were giving up 
the old ideas that the environment      

supplied food1 as such1 to plants1 and  
had recognised that the plant takes up  
substances from without and rearranges  
these in its own body4  ,the next twenty
 years or so form a very dark interval  
in plant physiology1 chiefly owing to   
the influence of the assumption of a    
special vital force1 an assumption which
 was not allowed merely to serve as a   
hypothesis put forward to stimulate     
research and suggest better ideas1 but  
which gained a hold over men's powers of
 reasoning to an extent which now       
appears monstrous and phenomenal4  ,many
 errors crept in during this reign of   
terror1 one of the most fatal of which  
was ,de ,candolle's revival of the idea 
of spongioles2 and another1 equally     
disastrous in many of its effects1 was  
the conception of a sort of vegetable   
food-extract1 humus1 existing in the    
soil in a form peculiarly suitable for  
direct use by plants4 ,it was during    
this period that the confusion between  
the processes of respiration and        

carbon-dioxide assimilation arose1 and  
exerted its effects for evil into our   
own day4  ,the now astounding statement 
that oxygen-respiration in plants did   
not occur1 laid the foundation of many  
subsequent difficulties1 and so did the 
positive and authoritative views on the 
uses of minerals to the plant4 ,liebig1 
in fact1 stood in the invidious position
 of being a high authority on purely    
chemical questions1 who was impelled to 
give opinions on matters which can only 
be solved by physiological experiments3 
his great service was to clear up       
mistakes as regards the chemistry of    
soils and of plants--his great mistakes 
were due to his pronouncing on          
physiological matters2 and it may be    
doubted whether his great services to   
the purely chemical side of subjects    
connected with agricultural matters are 
the more to be admired1 or the          
disastrous influence of his statements  
on subjects which do not belong to the  
domain of chemistry should be the more  

deplored4 ,be that as it may1 he handed 
on to succeeding generations some       
weighty errors as regards plant-life1   
and taught the agriculturist to regard  
chemical analyses of soils and plant    
ashes with a reverence which obstructed 
progress for some time4 ,as a set-off to
 this we must place his contributions to
 the destruction of the bugbear         
vitalism1 which was simply preventing   
enquiry1 and his services in bringing   
together and sifting with power and     
originality all that had been then      
acquired as regards the chemistry of the
 plant1 the soil1 and the atmosphere4   
,that ,liebig was indispensable in      
#ahdj-ahej is one thing2 but that his   
influence should extend to the present  
day is quite another1 and his inevitable
 mistakes were almost as powerful for   
future evil1 as his clear exposition of 
the chemistry of his day was productive 
of immediate good4  ,boussingault1      
working at the same time1 #ahcg-ahee1   
but experimentally with the living      

plant1 taught us more about these       
matters than any investigator of the    
time1 though it is very probable that   
the stimulus of ,liebig's speculations1 
good and bad1 had its effect in         
impelling ,boussingault to devote his   
splendid methods to problems of         
plant-nutrition4 ,boussingault's        
contributions to our knowledge of the   
composition of the dead plant cannot be 
over-estimated2 but he did more than    
this1 because he so clearly apprehended 
the necessity for asking his questions  
directly of the living plant1 instead of
 deducing from chemical principles what 
might be supposed to occur in it2 and   
although future researches showed that  
even so careful an investigator solved a
 problem of first importance--viz4 the  
question of the fixation of free        
nitrogen--the wrong way1 it will be     
found that so far as he did go his      
conclusions were sound1 and well        
calculated to inspire the confidence    
with which the world received them4 ,as 

we are here concerned more especially   
with the botany of agriculture1 however1
 it is unnecessary to dwell longer on   
these matters1 or on the similar and    
even more extensive experiments1 of     
world-wide reputation1 carried on for so
 many years1 and still being carried on 
under the liberal auspices of ,sir ,john
 ,lawes1 at ,rothamsted4 ,moreover it   
may be necessary to return to some of   
these points later on4   ,,notes ,,to   
,,chapter ,i4       ,the reader will    
find a further general account of these 
matters in ,sachs' ,lectures on the     
,physiology of ,plants1      especially 
,lectures ,i4 and ,,xii41 ,engl4 ed41   
,oxford1 #ahhg4 ,he      may then       
proceed to ,pfeffer's ,physiology of    
,plants1 ,engl4      ed41 #ahii1 chapter
 ,i41 and to the account of the history 
of      the subject in ,sachs' ,history 
of ,botany1 ,oxford1 #ahij1             
especially pp4 #cei-cge and #dde-ebd4   
,references to more special             
literature will be found in ,pfeffer4   

,,chapter ,,ii4  ,,the ,,plant ,,and    
,,its ,,food4       ,the food of        
plants--,vital force--,other            
errors--,liebig and                     
,boussingault--,the botany of           
agriculture4 ,the synthesis of          
carbohydrates--,the physiology of       
plant-nutrition4 ,the      persistence  
of misconceptions4   ,the year #ahfj may
 be regarded as a landmark of importance
 in the history of plant physiology1 for
 it was in that year that ,sachs        
discovered that the bringing together of
 water and carbon-dioxide1 in the green 
chlorophyll-corpuscles of the plant     
exposed to sunlight1 results in the     
formation of the grains of starch found 
in these corpuscles4  ,previous to this 
date ,dutrochet 7#ahbf-cg7 had          
introduced the then crude idea of       
osmosis into physiology2 vegetable      
anatomy had improved1 and the modern    
conceptions of the living cell1         
protoplasm1 nucleus1 etc41 were slowly  
looming2 sieve-tubes had been           

discovered1 and the proteids and starch 
in various parts of the plant examined2 
and the suggestion was abroad1 replacing
 ,liebig's idea that plant acids were   
the first products of                   
carbon-assimilation1 that some          
substance1 of a slimy nature1 was       
manufactured in the cells of the leaves 
and thence distributed as the formative 
material from which the plant           
constructed its parts4 ,davy and        
,boussingault had even surmised that a  
carbohydrate might be the first-formed  
product in assimilation4  ,there can be 
little doubt that ,sachs' classical     
proof1 by direct physiological          
observation and experiment1 first       
brought forward the truth of organic    
synthesis in the plant in a concrete and
 convincing form4  ,but it did more than
 that4 ,it laid the foundation of the   
modern physiology of plant-nutrition on 
ground already prepared by ,de ,saussure
 and the earlier workers2 for1 in       
addition to emphasising the truth of    

organic synthesis--a truth which had    
been gradually impressing itself on the 
world for some years--,sachs' discovery 
showed clearly the real meaning of      
carbon-assimilation as a process for    
obtaining combustible food1 which the   
plant then proceeds to make use of4     
,many points were rapidly cleared up at 
once1 or if not explained were at least 
put into a strong light for further     
enquiry1 and plant-nutrition soon ceased
 to be the mysterious subject for all   
kinds of wild conjectures that it had   
hitherto been4  ,the meaning of thin    
leaves1 with numerous stomata and finely
 ramified or divided vascular bundles1  
became more apparent1 as also did the   
significance of the ascending           
transpiration current2 the storage of   
starch-grains in tubers1 medullary rays1
 roots1 seeds1 etc41 obtained meanings  
not understood before2 the spread of    
roots in the soil1 and the gradually    
discovered properties of the finer      
rootlets and of the root-hairs1 fitted  

naturally into their places2 and1 in    
short1 a thousand facts1 otherwise      
isolated1 became collated into an       
intelligible system1 full of suggestions
 for new work1 such as has since gone on
 and is now being pursued with an       
activity and success never before       
realised in the history of science4  ,as
 time went on1 while the general truth  
of ,sachs' views was confirmed1 a number
 of detailed discoveries were made which
 seemed to contradict them in certain   
points4 ,it was found that not all      
leaves form starch1 for some contain    
sugar or oil2 but ,holle and ,godlewski 
proved experimentally that this oil may 
be replaced by starch if the conditions 
of assimilation are slightly modified4  
,more recently ,hebert discovered that  
the stalks and leaves of grasses contain
 a peculiar form of gum1 which was      
formerly confounded with starch1 a      
substance not abundant in them4 ,then   
came ,schimper's discovery of           
starch-forming corpuscles1 which1 if    

supplied with sugar1 are able to form   
starch-grains in the dark1 as in tubers1
 etc41 underground2 and as subsequent   
researches have proved that the         
chlorophyll-corpuscles--which are       
morphologically the same as the         
starch-forming corpuscles and can be    
replaced by them--are also able to form 
starch-grains from sugar1 as proved by  
the experiments of ,boehm1 ,acton1      
,meyer1 ,laurent1 ,bokorny1             
,saposchnikoff1 and others1 it soon     
became evident that nothing essential   
needed altering in ,sachs' view that    
starch is the first visible product of  
carbon-dioxide assimilation1 only it    
became clearer that the starch-grains   
are built up by the protoplasm from     
glucose or some similar body1 and       
represent so many packets of reserve    
materials put by for the present because
 not required for the immediate needs of
 the cell4  ,boussingault showed1 about 
thirty years ago1 that assimilation soon
 stops in green leaves if cut off from  

the plant1 not because the leaves die1  
but owing to some maximum capacity being
 attained4 ,sachs had shown that the    
starch passes down to other parts of the
 plant in solution as glucose4  ,neither
 time nor space will permit me to go    
into the enormous field of research and 
results opened up by these and similar  
observations made between #ahfj-gj4 ,it 
must suffice to say that they led to the
 discovery and study of the diastatic   
and other enzymes in the leaves and     
other green parts of plants1 and to a   
clearer understanding of what was       
already known of them in seeds1 and this
 knowledge reacted at once on our       
insight into the processes of transport 
of reserve materials and constructive   
materials from one part of the plant to 
another1 matters which will be referred 
to later on4  ,it remains to explain    
,boussingault's difficulty as regards   
the cessation of assimilation4 ,recent  
researches confirm the view that at     
least three causes are at work to bring 

about the inhibition of the             
carbon-assimilation3 first1 the         
chlorophyll-corpuscles become filled to 
excess with starch1 which cannot get    
away because all the passages are full  
and the products are inhibiting the     
further action of the enzymes which     
should dissolve the solid granules2     
secondly1 the leaf being detached from  
the plant explains why the soluble      
products cannot get away1 for this makes
 a great difference in the rate of      
exhaustion of the leaf2 and1 thirdly1   
the same fact involves that the leaf can
 obtain no further supply of salts of   
potassium1 etc41 without which elements 
the processes in question cannot go on4 
,these and numerous other deeper        
insights into the process of            
assimilation1 obviously strengthen the  
force of ,sachs' discovery2 though it by
 no means necessarily follows that      
starch-grains are always the resting    
form of the products of assimilation1   
and we now know that such is often not  

the case3 we now have much deeper       
glimpses into the initial products of   
carbon-assimilation than ,sachs had in  
#ahfj1 but this enhances rather than    
detracts from the importance of his     
splendidly worked-out discovery4 ,put   
more generally1 we may now say that the 
process of carbon-dioxide assimilation  
in green leaves under the influence of  
light is a process of                   
synthesis--photo-synthesis--resulting in
 the building up of a carbohydrate such 
as sugar1 inulin or starch from the     
elements carbon1 hydrogen and oxygen4   
,but it must not be supposed that the   
importance of ,sachs' discovery1 and the
 rapid consequent extensions of our     
knowledge1 did their work forthwith in  
disabusing men's minds of old and       
erroneous notions4 ,to say nothing of   
numerous smaller misconceptions which   
still held their ground owing to the    
stupendous ignorance of plant-physiology
 which prevailed1 we find incompetent   
teachers and text-books were still      

propagating ideas worthy of ancient     
times4 ,the confusion between           
oxygen-respiration and the gas          
interchanges in carbon-assimilation was 
by no means eliminated even recently1   
though it can no longer withstand the   
deliberate onslaughts now made on it4   
,that the roots take up food as such    
from the soil1 and that that food is    
directly employed by the plant for its  
nutrition is even yet implied in daily  
conversation around us2 and although    
matters have advanced so far that       
everyone now knows that the substances  
at the roots must be in solution1 ere   
they can be received into the plant1 it 
sometimes leads to astonishing replies1 
if we press the question very far as to 
how the absorption takes place1 in an   
elementary examination of agricultural  
students4 ,that manures are foods to the
 plant1 that sap circulates1 that       
transpiration is of use to keep the     
plant cool1 and wood is a porous body1  
etc41 are only a few of the             

misconceptions still current1 in a      
decade that has found publishers for a  
work advocating that roots are congealed
 sap1 and that the leaves of plants     
absorb the moisture and dust of the air1
 and so provide the plant with food1 and
 for a paper explaining the action of   
root-hairs as tubes with open pores at  
their tips4 ,but the gravest            
misapprehensions current among us are   
due to the crude ideas as to what a     
plant really is3 this1 ,i take it1 is   
owing to the difficulty of grasping what
 physiologists mean by organised        
structure1 and leads to regarding the   
living being either as a mere           
aggregation of chemical compounds1 built
 up by the ordinary play of chemical    
forces1 as we know them1 acting on dead 
matter1 or1 as in the days before       
organic chemistry1 as a mysterious      
entity endowed with vital force1 and    
with properties not amenable to         
scientific investigation4 ,the mistaken 
notions as to the powers of roots to    

select those substances which the plant 
requires1 and to reject useless ones was
 merely an expression of this belief4   
,the rock on which all are liable to    
come to grief--the chemist or physicist 
who requires all his facts in terms of  
analyses and proportions by weight1 and 
therefore takes too mechanical a view of
 the subject1 or the man who is not     
scientifically trained at all1 and      
therefore is more liable to go to the   
other extreme and regard the plant as a 
mysterious something which grows and has
 poetical associations and              
traditions--is the great fact of        
organised structure1 and it is the      
recognition of this fact and some of its
 consequences which has altered the     
whole position of the subject1 and      
brought the study of the plant into the 
domain of physiology4 ,the living plant1
 its structure and organisation1 the    
functions of its mechanism1 and its     
relations to the environment1 thus forms
 a subject apart from that which        

concerns the chemical composition of the
 plant and its environment1 and this    
distinction designates1 in a word1 as it
 were1 the change which has been brought
 about by modern biology4  ,a point to  
be emphasised to the utmost where       
agricultural students are concerned is  
that the essential process of feeding is
 the same in a green plant1 a fungus1   
and an animal2 the greatest confusion   
still exists with regard to this matter1
 owing to misconceptions as to the real 
meaning of the functions of the         
chlorophyll-corpuscles when supplied    
with carbon-dioxide and water and the   
energy of the sun's rays4 ,the plant    
does not feed on carbon-dioxide1 any    
more than it feeds on oxygen--it feeds  
on the organic material after it has    
been constructed1 and the               
chlorophyll-function is merely one mode 
of obtaining supplies of such organic   
substance4   ,,notes ,,to ,,chapter     
,,ii4       ,in addition to the         
references in the last chapter1 the     

student      should consult ,sachs'     
,lectures1 ,,xvii4-,,xix41 and          
,pfeffer's      ,physiology1 pp4        
#bhg-cbi1 for the further development of
 this      subject4 ,an excellent       
resume1 with new facts and points of    
view1 will be found in ,dr4 ,horace     
,brown's ,address to the      ,chemical 
,section1 ,british ,association         
,reports1 ,dover1 #ahii2      and       
,chemistry and ,physiology of ,foliage  
,leaves in ,trans4      ,chem4 ,soc41   
#ahic1 p4 #fjd4 ,see also ,blackman1    
,experimental      ,researches on       
,vegetable ,assimilation and            
,respiration1 ,phil4      ,trans41      
#ahie2 and ,parkin1 ,formation1 etc41 of
 ,carbohydrates      in ,monocotyledons1
 ,phil4 ,trans41 #ahii4     ,,chapter   
,,iii4  ,,the ,,plant ,a ,,living       
,,machine4       ,the plant a machine   
into which energy and material are      
taken--,carbon                          
assimilation--,feeding--,accumulation   
and      transformations in the plant4  

,the action of light--,the              
chlorophyll-function4   ,the relations  
of the plant to the environment can only
 be understood by taking into account   
the results of modern physiological     
discoveries4 ,these teach us that the   
living plant is a highly complex        
machine1 the details of its organisation
 and structure being much more numerous 
and much more closely correlated at     
numerous points1 than the parts of any  
other machine known to us4  ,they also  
teach us that it is supplied with energy
 from without1 as any other machine2 and
 that when so supplied1 and properly    
working1 the living structure or        
machinery does work1 also as other      
machines4 ,but modern physiology goes   
further1 in that it renders some account
 of the ways by which the external      
energy is taken into the plant1 and     
there applied to do work1 or stored up  
for a time in order that it may be used 
to do work at some future time4  ,the   
accumulation of energy thus ensured is  

associated with corresponding changes of
 material substance1 and the principal  
means for bringing this about is        
recognised in the assimilation of       
carbon-dioxide--photo-synthesis4  ,in   
this process energy enters the          
chlorophyll-corpuscle in the form of the
 radiant energy of the sun1 it is there 
directed in the mechanism of the        
protoplasm1 so as to do work on the     
molecules of water and carbon-dioxide   
which have also been brought into the   
machinery2 this it does1 breaking       
asunder their stable structure into     
unstable bodies1 which then re-combine  
in different ways to form a             
carbohydrate1 such as starch1 and this  
starch is temporarily stored as grains1 
while oxygen escapes4  ,each            
starch-grain1 therefore1 is to be       
regarded as a packet of matter and of   
potential energy1 as it were1 capable of
 yielding up the latter at any future   
time1 when put under such circumstances 
that it must do so4 ,such stores of     

energy-yielding substance1 if ,i may use
 the much-abused phrase1 form the       
principal food of the plant--or of an   
animal1 if it steps in and takes        
them--and we now see that the process of
 carbon-dioxide assimilation1 as it has 
perhaps unfortunately been called1 is   
not the same thing as the process of    
feeding1 for the feeding--i4e4 the      
nutrition proper--of the plant does not 
begin until the food has been thus      
obtained4  ,we now see what the real    
position of the plant is1 to its        
environment1 whether the latter be      
living or dead4 ,from our point of view1
 the plant serves as a centre for       
bringing together the substances        
obtainable from the soil1 and those     
derived from the atmosphere1 and so     
focussing and directing the radiant     
energy of the sun upon these substances1
 that they are broken up1 and some of   
their constituents synthesised1 with    
absorption of energy1 into a body1 such 
as starch1 containing more energy than  

did the original substances taken       
together or separate4 ,it matters little
 whether the actual carbohydrate thus   
synthesised is starch1 or sugar or      
inulin3 the point is that energy has    
been gained from outside and bound up   
with the acquired material for further  
use4 ,but modern physiology has carried 
matters much further than this1 and     
especially in the three following       
directions4  ,in the first place1 it has
 shown that much of the energy thus     
stored from without in the plant is     
again liberated in the process of oxygen
 respiration1 and expended partly as    
appreciable heat and partly as driving  
force for stimulating the machinery of  
the living plant to further activities4 
,in the second place1 part of it is     
rearranged with the rearrangement of the
 molecules with which the energy is     
bound up1 as it were1 so that work of   
various kinds is done in the machinery  
of the plant3 ,i refer to various       
metabolic and surface-actions resulting 

from the peculiar mode of presentment of
 the resulting substances1 for instance 
the production of osmotic pressures in  
the cell4  ,and1 thirdly1 part of the   
synthesised substance is worked up into 
higher bodies1 by processes which       
obviously entail the further doing of   
work on the constituents4  ,the further 
pursuit of this theme would evidently   
carry us beyond the more immediate      
subject of this book2 but ,i want to    
make clear that recent researches render
 it more and more certain that the      
living plant is a complex piece of      
co-ordinated machinery which brings     
together matter and energy from the     
external universe1 and then gets work   
out of these4  ,this proposition is the 
more important because the whole        
question of the enrichment of our planet
 with new food1 new building materials1 
and new fuel1 to compensate the daily   
losses1 depends on it1 and is of course 
to be referred fundamentally to the     
acquirement of new supplies of energy   

from the sun4 ,enormous activity has    
been displayed by physiologists1 since  
#ahfj1 in attempting to solve the       
question1 which of the many different   
rays known to proceed from the sun are  
absorbed by the chlorophyll-corpuscle1  
and directed to the performance of the  
work above referred to4  ,the names of  
,draper1 ,sachs and ,pfeffer stand forth
 prominently as pioneers in this2 while 
those of ,lommel1 ,engelmann1           
,timiriazeff and ,langley have been     
among the most active in making         
important contributions to the subject1 
and in attempting to answer the further 
questions connected with the mode in    
which the chlorophyll is concerned in   
utilising the energy of the solar       
radiations4 ,the point is one of supreme
 importance1 because it goes on all     
fours with modern questions as to the   
rays of light absorbed or dispersed in  
our atmosphere at different seasons of  
the year1 or in special climatic        
conditions1 to say nothing of its other 

scientific aspects4 ,unfortunately1     
however1 we have no satisfactory        
explanation of the actual role played by
 the chlorophyll substance itself1 in   
spite of much industrious work which has
 been done in the subject in this       
country and elsewhere4 ,as regards the  
rays employed1 it was first proved that 
the most effective belong to the red end
 of the visible spectrum1 and that the  
effect as measured by the amounts of    
oxygen given off1 and of starch formed  
in given periods of time1 is more or    
less proportionable to the intensity of 
the solar light4 ,then it was           
established that no monochromatic light 
is so powerful as the white light from  
which it was obtained1 though the       
relative numbers expressing the activity
 in the red and yellow regions may stand
 to those in the blue as something like 
#ab3a4 ,the latest results place the    
maximum assimilation in the red-orange1 
and this coincides with the maximum     
absorption in the chlorophyll4 ,if we   

may accept the current views as to the  
distribution of energy in the spectrum  
of solar light1 which depends on the    
complete absorption of all the rays by a
 black body1 where they are estimated as
 heat1 we have the interesting result   
that the agricultural or forest plant is
 adapted to catch and retain1 broadly   
speaking1 just those particular rays    
which possess most energy4  ,the        
probability is increasing that the      
protoplasmic machinery is the really    
effective mechanism in the process1 and 
we may figure this machinery as so      
holding or presenting the molecules of  
carbon-dioxide and water to the impact  
of the light-vibrations1 that the latter
 are enabled to undo the molecular      
structure2 the atomic combinations      
thereby liberated may then be supposed  
to form a body like formic-aldehyde1    
which by polymerisation becomes a       
carbohydrate of the nature of a sugar   
such as glucose1 which the protoplasm   
then builds up into its substance and   

subsequently deposits as starch1 and    
stores temporarily in the form of grains
 or as amorphous material4  ,this is    
partly hypothetical1 and is largely due 
to the careful deductions of the        
chemists1 but there are very many facts 
now to hand which bear out its          
probability1 especially the recent      
advances in our knowledge of the sugars1
 and the experimental feeding of leaves 
and plants deprived of starch with such 
substances as dextrose1 levulose1       
maltose1 and other sugars1 as well as   
glycerine and other bodies which should 
be convertible into1 or yield them1 if  
the theory is true4 ,in this last       
connection1 the careful and extensive   
experiments of ,acton1 ,a4 ,meyer1      
,boehm1 and ,laurent should be          
mentioned4 ,it would be interesting to  
enlarge upon ,engelmann's beautiful     
physiological experiments in connection 
with this subject of absorption of solar
 energy1 where the maximum accumulation 
of oxygen-loving bacteria at those parts

 of a green alga which lie in the       
red-orange of the spectrum1 are used as 
indicators of the maximum oxygen        
evolution 7and therefore of the maximum 
carbon-dioxide assimilation71 but space 
will not admit of this4 ,for a similar  
reason ,i must also pass over the same  
observer's experiments with plants which
 assimilate in protoplasm behind a red  
instead of a green substance1 and which 
absorb chiefly other rays between the   
yellow and blue1 with the remark that   
they also seem to imply that it is the  
protoplasmic machinery which turns the  
energy on to the carbon-dioxide         
molecule1 the coloured screen being     
secondary in the matter4 ,recent        
experiments which show that green plants
 will not assimilate carbon-dioxide in a
 light which has passed through a       
solution of chlorophyll--and therefore  
left its red rays behind2 nor behind a  
screen of iodine dissolved in           
carbon-dioxide--which lets no visible   
rays between the red and blue           

pass--should be noticed1 as showing the 
importance of the chlorophyll and the   
special rays referred to1 however2 and  
,i ought at least to mention            
,timiriazeff's beautiful proof1         
published in #ahij1 that if1 on the leaf
 of a plant left in the dark long enough
 to render it free of starch1 a bright  
solar spectrum is steadily projected for
 #c-f hours1 the chlorophyll then       
removed by alcohol and the decolorised  
leaf placed in iodine1 the image of the 
spectrum is reproduced by the different 
intensities of the starch bands1 blue   
with iodine1 in the different parts4    
,here1 again1 the maximum coloration    
coincides with the maximum absorption in
 and near the red4  ,microscopic        
observations and photo-chemical         
experiments alike convince us that the  
chlorophyll-corpuscle is itself a       
complex piece of protoplasmic machinery1
 working for and with the rest of the   
plant1 and there can be little question 
as to the greater accuracy of our       

reasoning on the whole question ,i am   
discussing1 since ,meyer1 ,schimper1    
,pringsheim1 and others have established
 the importance of its structural       
peculiarities4  ,i must now pass on to  
consider another aspect of the question 
of carbon-assimilation4   ,,notes ,,to  
,,chapter ,,iii4       ,in addition to  
the references in the last chapter1 the 
reader      may be referred to ,sachs'  
,lectures1 ,,xxv41 and ,pfeffer's       
,physiology1 pp4 #cbi-cef1 where the    
voluminous literature is      given4    
,,chapter ,,iv4  ,,metabolism4          
,quantities of starch formed1 and their 
significance for the      plant4 ,the   
absorption of energy--the conversion of 
energy in      the plant4 ,the plant is 
a complex machine for concentrating     
and storing energy and material from    
without4   ,sachs measured the increase 
in dry weight 7due to the carbohydrates 
formed in the chlorophyll-corpuscles7   
per square meter of leaf-surface1       
exposed for a definite period1 by drying

 rapidly at #ajj deg4 ,c4 equal areas of
 the leaves concerned1 and comparing the
 weights4  ,of course the results are   
not to be pushed too far1 in view of the
 fact that some of the starch is        
continually passing away to be utilised1
 and of the difficulties of comparing   
the weather1 the intensity of light1    
currents of air1 hygroscopic conditions 
of atmosphere1 and other variable       
factors which influence the matter4 ,for
 instance1 the stomata open and close to
 different extents according to the     
conditions of light and moisture1 and   
this affects the whole mechanism of     
transpiration especially1 and therefore 
the supplies of water and mineral salts4
 ,nevertheless1 some interesting and    
valuable results have been obtained in  
connection with this important subject4 
,it was found1 for instance1 that the   
foliage of a sun-flower or of a         
vegetable-marrow may be forming starch  
at a rate of considerably over a gram   
per hour in every square meter of       

leaf-surface exposed on a fine day2     
while in particularly clear and warm    
sunny weather ,sachs obtained as much as
 #bd to #be grams per square meter per  
diem4  ,when one reflects that #bjj     
square meters is not an extravagant     
estimate for the area of leaf-surface   
exposed on a tree1 for a period which   
even in our latitudes may be            
considerably over #ajj days of1 say1 ten
 hours' light1 we need no longer wonder 
at the rapidity with which wood is      
produced in the stems1 and similar      
estimates 7which ,i have purposely kept 
lower than the estimates for continental
 and tropical climates7 may suffice to  
show how quickly potatoes or the ears of
 corn1 etc41 may fill up with the starch
 or other carbohydrates which render    
them valuable as crops4 ,we want more   
measurements in these connections1      
moreover1 for there are several ways in 
which they are of scientific value and  
practical importance4  ,it is evident   
from what has been said that every grain

 of starch formed represents so much    
energy1 packed away for the moment in   
the storehouses of the plant2 and we    
know that--quite apart1 however1 from   
intermediate transformations of the     
energy thus stored--this energy         
reappears in the kinetic state          
eventually1 when the starch is burned   
off1 in presence of oxygen1 and         
transformed into carbon-dioxide and     
water4 ,it matters not how quickly or   
how gradually this combustion occurs1 or
 whether it is accomplished by burning  
in a fire1 or by slow and complex stages
 in respiration or metabolism3 the point
 is that the unit of weight of starch   
yields so many units of heat when its   
structure tumbles down to the original  
components1 carbon-dioxide and water4   
,clearly1 if we know how many units of  
heat are yielded by the combustion of   
one gram of starch1 we can obtain an    
estimate of the amount of energy1       
measured in terms of heat1 which the    
foliage gains and stores up--an estimate

 which will approach the truth in       
proportion as our estimate of the total 
assimilative activity is correct4  ,a   
word of warning is necessary here1      
however1 for those best acquainted with 
physiology recognise that however useful
 such calculations as the above may be1 
and undoubtedly are1 to give a general  
idea of the fact that the energy        
represented is large1 it would be a     
mistake to suppose that such estimates  
give even an approximate measure of the 
energy of potential which may be got    
from the carbohydrate1 and still less of
 the amount of work that may be got from
 its employment1 according to the way it
 is employed or presented in the plant4 
,to take a single instance only4 ,if the
 carbohydrate is rapidly burned off to  
carbon-dioxide and water1 very little is
 got out of it in the way of work--most1
 if not all1 of the energy set free     
escapes as heat3 whereas if the         
carbohydrate is slowly and gradually    
oxydised1 passing through various stages

 and giving rise to powerfully osmotic  
bodies in the process1 or if it is built
 up into protoplasm1 or into the        
structure of a cell-wall1 relatively    
enormous quantities of work may be got  
out of its surface-energy1 and heat may 
be absorbed4 ,whence it follows that we 
cannot measure the power for            
physiological work of a body by merely  
obtaining its heat of combustion1 any   
more than we can infer its significance 
in metabolism from its chemical         
properties4  ,the general conclusion    
that the plant stores large quantities  
of energy may of course be arrived at by
 simply estimating the enormous         
quantities of food-material which we    
obtain annually from agricultural       
plants4  ,modern physiologists have     
attempted to proceed further than this1 
however1 in their essays to form an     
estimate of the relations between the   
available energy in the solar rays and  
that used and stored in the plant4  ,if 
we reflect on such phenomena as the cool

 shade of a tree1 and the deep gloom of 
a forest1 and on experiments which show 
that an ordinary leaf certainly lets    
very little of the radiant energy of the
 spectrum pass through it1 it becomes   
evident that many of the rays which fall
 on the leaf are absorbed in some form1 
and it becomes very probable that much  
of the solar energy1 other than that we 
term light1 is retained in the leaf for 
other purposes than assimilation--or1 at
 least1 no other conclusion seems       
possible in view of all the facts4      
,engelmann's researches with purple     
bacteria are almost conclusive on this  
point1 and we may regard it as extremely
 probable that the plant makes other    
uses of rays1 perceived by us as        
heat-rays1 as sources of energy4        
,researches on the influences of        
temperature on assimilation and other   
functions point to the same conclusion2 
and ,pfeffer and ,rodemann definitely   
state that heat is converted into work  
in the osmotic cells4 ,and the study of 

the absorption bands in the spectrum of 
the living leaf becomes more            
intelligible in the light of these      
conclusions4 ,moreover1 the fact that a 
plant still carries on processes of     
metabolism when active transpiration has
 lowered its temperature below that of  
the surrounding air--and the plant      
therefore receives heat from the        
environment--points to similar          
conclusions4  ,the importance of the    
conclusion is immense1 for even if the  
plant had no other sources of energy    
than the darker heat rays of the solar  
spectrum1 it is clear that it ought to  
be able to do work4  ,the above may     
suffice for the general establishment of
 the conclusion that the plant absorbs  
more radiant energy than it employs     
solely for assimilation1 and emphasises 
our deduction that it is a machine for  
storing energy4  ,the question now      
arises1 how is this relatively enormous 
gain in energy employed by the plant8   
,our answer to the question is not      

complete1 but modern discoveries in     
various directions have supplied clues  
here and there which enable us to sketch
 in some degree the kinds of changes    
that must go on4  ,not the least        
startling result is that1 important as  
carbon-assimilation is as the chief mode
 of supplying energy1 it is not the only
 means that the plant has of obtaining  
such from the environment1 and it is    
even possible--not to say probable--that
 energy from the external universe may  
be conveyed into the body of the plant  
in forms quite different from those     
perceptible to our eyes as light4  ,in  
the most recent survey of this domain1  
it is pointed out that we may           
distinguish between radiant energy1 as  
not necessarily or obviously connected  
with ponderable matter1 and mechanical  
energy1 which is always connected in    
some way with material substance4 ,all  
mechanical performances in the plants   
depend on transformation of some form of
 these1 evident either as actual energy 

doing mechanical work1 or as energy of  
potential ready to do work4  ,in so far 
as molecular movements are concerned1 we
 have the special form of chemical      
energy4 ,the evolution of heat1 light   
and electricity by plants are instances 
of radiant energy1 and so on4  ,many    
transformations of energy in the plants 
are due to non-vital processes--e4g4    
transpiration1 warping actions1 etc41   
but we cannot always draw sharp lines   
between the various cases4 ,nor can we  
directly measure the work done in the   
living machinery2 but from the effects  
of pressures and strains1 the lifting of
 heavy weights1 driving of root-tips    
into soil1 osmotic phenomena1 etc41 it  
is certain that the values may be very  
high4  ,the following classes of        
processes in living protoplasm and cells
 may be taken as indicators4 ,first we  
have transformation of chemical energy1 
without which continued life is         
impossible3 in many cases--e4g4 the     
processes connected with oxygen         

respiration--these result in the        
development of heat4 ,secondly1 we have 
those remarkable manifestations of      
energy known as osmotic processes1 which
 depend on surface actions1 and with    
which may be associated other surface   
effects1 such as imbibition1 secretion1 
etc41 and in connection with which heat 
may be evolved or absorbed4 ,it is true 
the substances which exhibit the        
properties here referred to may be      
produced1 or placed in position1 by     
chemical energy1 or they may be absorbed
 by roots1 etc42 but the proximate      
energy exhibited by them is not derived 
from chemical energy1 and may be out of 
all proportion to the chemical energy of
 the substance or substances concerned4 
,moreover it is significant to note that
 a highly oxydised body may develop much
 osmotic energy1 as well as a highly    
combustible one4  ,it is of the greatest
 importance to realise the truth that   
much work can be1 and is done in the    
living plant1 by conversions of energy  

of potential independent of and out of  
proportion to the chemical energy       
available by decomposing the substances 
concerned2 even the heat of respiration 
may be superfluous here1 for the plant  
may absorb heat from without1 and       
convert it into work4  ,tensions often  
arise in the plant1 and do work         
expressed as movements--e4g4 the        
springing of elastic ,balsam fruits1    
stamens of ,parietaria1 etc4  ,osmotic  
energy not only results in enormous     
pressures and tensions1 but causes      
movements by diffusion and diosmosis1   
and any given osmotic substance which   
carries this energy with it is not      
necessarily formed always in the same   
way in the cell--e4g4 glucose may arise 
from starch1 or from carbon-dioxide1 or 
from oil4  ,surface-energy is also      
expressed in the powerful attractions   
for water exhibited in imbibition1      
swelling1 capillarity1 absorption1      
surface tensions1 etc4  ,transpiration  
induces relatively enormous disturbances

 of equilibrium1 and does work in moving
 water quite independent of chemical    
energy4  ,again1 what may be termed     
excretion-energy1 as expressed in the   
separation of a solid body--e4g4 a      
crystal--from a solution1 may be for our
 purposes regarded separately4 ,any     
change in the condition of aggregation  
of a substance in the plant may result  
in movements and the overcoming of      
resistances4  ,it will be evident from  
this short digression--and this is the  
point ,i wish to emphasise--that in the 
interval between the securing of a grain
 of starch1 representing so much energy 
won from the external universe1 and the 
reconversion of this grain into its     
equivalent carbon-dioxide and water1 by 
respiration1 resulting in the loss of   
the above energy as heat1 the starch    
referred to may have undergone numerous 
transformations in the living machinery 
of the plant1 and have played at various
 times a role in connection with the    
most various evolutions of energy4  ,if 

we try to picture a possible case1 we   
may take the following4 ,a given        
starch-granule1 after being built up in 
the chlorophyll-corpuscle1 is           
decomposed1 and yields part of itself as
 glucose1 which passes down into other  
parts of the plant in solution4 ,part of
 it is merely re-converted into starch1 
and temporarily stored3 another part    
passes into the arena of                
oxydation-processes1 the sum of which   
constitute respiration1 and may serve   
for a time in the molecules of an       
organic acid3 yet another part may be   
converted into a constituent of the     
cellulose cell-walls2 while part may be 
brought into play in the reconstruction 
of protoplasm4  ,in this last connection
 a discovery made by ,schulze about     
#ahgh1 and followed up later by         
,pfeffer1 ,palladin1 and others is of   
importance4 ,seedlings growing in the   
dark1 or in an atmosphere devoid of     
carbon-dioxide in the light1 become     
surcharged with nitrogenous bodies known

 as amides1 formed during the breaking  
down of the proteids in the destructive 
process preceding and accompanying      
respiration3 if the seedlings are       
allowed free access to light and        
carbon-dioxide1 however1 the amides     
disappear4 ,the explanation is that they
 are combined with some of the materials
 of the carbohydrates1 and again built  
up into the material of the living      
protoplasm4  ,returning to our          
hypothetical starch-grain--or1 rather1  
its parts--we have some of it retained  
as starch1 in excess1 simply because it 
is not needed at the moment3 another    
portion gives up its energy in          
respiration1 and this does work on the  
spot1 or is lost as heat2 or in the body
 of an organic acid1 or its salt1 the   
part in question may do lifting or      
pressing work by osmosis1 or cause      
diffusion-currents from one cell to     
another4 ,in the constitution of the    
cell-wall we may have part of our       
starch-grain aiding in imbibition or in 

the establishment of elastic tensions in
 turgidity3 and1 finally1 parts may be  
built up into the living protoplasmic   
machinery of the plant4  ,what is true  
for the starch-grain is also true for   
any particle of salt1 or water1 or gas  
which enters into the metabolism of the 
living plant1 regard being paid to the  
particular case1 and circumstances in   
each case4  ,enough has been said to    
show that the plant cannot be properly  
studied merely as the subject of        
chemical analysis or of physical        
investigation2 you might as well expect 
to understand a watch by assays of the  
gold1 silver1 steel and diamonds of     
which its parts are made up1 or to learn
 what can be got out of the proper      
working of a lace machine by analysing  
the silk put into it1 and the fabric    
which comes out1 and by taking the      
specific gravity of its parts and       
testing the physical properties of its  
wheels and levers4  ,this is not the    
same thing as denying the value of such 

knowledge1 in the case of either the    
dead machine or the living plant3 it is 
merely emphasising the supreme          
importance of the study of the structure
 and working of the active machinery in 
both cases4  ,nor is it pertinent to    
remark on the apparent hopelessness of  
physiology being at present able to     
explain the seemingly infinite          
complexity of the living machinery of   
protoplasm and its activities4 ,the     
modern locomotive is also a complex     
affair in its way1 but it is profitable 
to investigate it and to know all one   
can of its working and possibilities1   
for obvious reasons3 a little reflection
 will convince us that it is also worth 
while to investigate that complex       
machine1 the plant--the working organism
 which alone can really enrich a        
country4 ,moreover1 we ought to be      
encouraged by the satisfactory progress 
now being made1 and the splendid        
practical results which are accruing1   
rather than dismayed by the prospect of 

unflagging labour which will be required
 in the future4  ,enough has perhaps    
been said to establish the general truth
 that the plant is a complex machine for
 storing energy and material from       
outside1 and we have seen that modern   
research has at least gone a long way   
towards determining how the living      
machine works4  ,it is hardly necessary 
to point out that important practical   
consequences may result from these      
phenomena of the accumulation of surplus
 starch or other carbohydrates in the   
leaves during the day1 and of their     
disappearance during the night into the 
lower parts of the plant4 ,for instance1
 foliage cut for fodder in the morning  
is far poorer in starch than if cut in  
the evening1 and it would be very       
instructive to have experiments made on 
a large scale to test the result of     
feeding caterpillars or rabbits1 for    
instance1 with mulberry1 vine1 or other 
leaves in the two conditions4  ,again1  
we now see what complications may arise 

if a parasitic organism gains access to 
the stores of carbohydrates in process  
of accumulation1 or attacks and injures 
the machinery which is building up such 
materials1 etc4   ,,notes ,,to ,,chapter
 ,,iv4       ,the student who desires to
 pursue this subject further should     
read ,sachs' ,lectures1 ,,xx4 and       
,,xxv41 and ,pfeffer's      ,physiology1
 pp4 #ddb-eff1 but he will hardly arrive
 at the      best that has been done    
without consulting ,pfeffer's ,studien  
zur ,energetik der ,pflanzen in the     
,abhandl4 der ,math4-,phys4      ,classe
 der ,kgl4 ,sachss4 ,gesellsch4 der     
,wiss4 7,leipzig1 #ahib71      p4 #aea2 
and ,kassowitz1 ,allgemeine ,biologie   
7,vienna1 #ahii71      ,bk4 ,i41 pp4    
#a-abg4     ,,chapter ,v4  ,,roots ,,and
 ,,root-,,hairs4       ,older views as  
to root-hairs--,root-hairs and their    
development--,surface--,variations--,con
ditions for maximum                     
formation--,minute structure--,adhesion 
to particles of      soil--,functions4  

,on the roots of most plants are to be  
found delicate1 silky-looking1 tubular  
prolongations of some of the superficial
 cells1 known as root-hairs4 ,malpighi  
7#afhg7 seems to have been the first to 
observe them1 and he took them for      
capillary tubes4 ,grew 7#afhb7 seems to 
have been responsible for the view that 
the roots act like sponges in taking up 
water4  ,simon 7#agfh7 was probably the 
originator of the idea that these       
root-hairs were excretory tubules1 a    
view that became very popular at the    
beginning of this century4  ,meyer      
7#ahch7 was perhaps the first to give a 
comparative account of them1 and he     
supposed them to be delicate            
prolongations of the root-surface to    
facilitate the absorption of water4     
,the real importance of these organs1   
however1 has only become apparent since 
,sachs1 in #ahei1 recognised their      
relations to the particles of soil      
between which they extend and to which  
they cling4  ,in #ahhc ,schwarz made a  

very thorough study of their biological 
character1 and in #ahhg ,molisch gave us
 new facts as to their physiology4 ,our 
knowledge of them has been rendered very
 much more intimate by the researches of
 ,pfeffer and ,de ,vries on osmotic and 
plasmolytic phenomena1 and they serve as
 an excellent study of some of the best 
results of modern physiology4  ,in the  
normal case1 such as is exemplified by a
 seedling wheat or bean1 the root-hairs 
arise some distance behind the growing  
tip of the root1 an obvious adaptation  
which prevents their being rubbed off by
 the soil1 as they would be if developed
 on parts still actively lengthening4   
,as those behind die off1 new ones      
replace them in front1 and so we find a 
wave of succession of functionally      
active root-hairs some little distance  
behind the tip of the root3 the same    
order of events holds for each new      
rootlet as it emerges from the parent   
root1 and so successive borings in the  
soil1 made by the diverging root-tips1  

are thoroughly explored by these        
root-hairs4  ,measurements have shown   
that in various plants the surface of   
root on #a mm4 of length is increased by
 the root-hairs in proportions given in 
the following table3                    
----------------------------------------
------------------------      ,,plant4  
,area of surface        ,area of        
,no4 of times                without    
root-hairs4  root and hairs4    greater4
                                        
----------------------------------------
------------------------   ,maize1      
#d4eb sq4 mm4         #be4ac sq4 mm4    
#e4e   ,pea1          #d4ga sq4 mm4     
#eh4cc sq4 mm4      #ab4d   ,scindapsus1
  #ad4jb sq4 mm4        #bfa4i  sq4 mm4 
#ah4g                                   
----------------------------------------
------------------------  --which       
sufficiently establishes the general    
proposition that the area of the        
root-surface is enormously increased by 
these hairs4  ,but this does not give us

 any definite idea of the length of the 
cylinders of soil explored by these     
surfaces1 until we find that plants such
 as an ordinary sunflower1 hemp1 or     
vegetable-marrow may have roots         
penetrating into a cubic meter of soil1 
in all directions1 and so closely that  
probably no volume so large as a cubic  
centimeter is left unexplored4 ,clark   
found by actual measurement that the    
roots of a large gourd1 if put end to   
end1 extended over #be kilometers1 and  
,nobbe gives #ebj meters for the roots  
of a wheat4 ,vetches may go nine feet   
deep1 and oats more than three feet4    
,the ,sal1 a tree of the forests of     
,india1 has roots which penetrate to a  
depth of #ej to #fj feet4  ,some rough  
notion of the lengths1 superficies and  
penetrating capacities of the roots of a
 large tree may be gathered from the    
above1 but it is doubtful whether we can
 form any adequate ideas as to the      
millions of root-hairs which must be    
developed along the course of these     

subterranean boring organs4  ,one of the
 most striking results of modern enquiry
 into these matters1 is the discovery   
that the number and superficial area of 
these root-hairs1 on one and the same   
plant1 may vary to a large extent       
according to the structure1 as it were1 
of the soil1 and the degree of moisture 
it is capable of retaining2 or1 with the
 same soil1 according to the amount of  
water which it receives and holds4      
,correlations have also been observed   
between the development in length and   
surface of the rootlets themselves4     
,the following illustrations will       
suffice to show this3  ,six young       
wheat-plants in soil kept constantly    
wet1 developed roots the total length of
 which measured #cfe mm4 each1 on the   
average1 and almost devoid of           
root-hairs4  ,six similar plants in soil
 only moderately moist1 averaged #ffh   
mm41 and were well furnished 7though not
 densely covered7 with root-hairs4  ,six
 similar plants in soil which would be  

termed dry1 averaged #cga mm41 but were 
densely covered with rich crops of      
root-hairs4  ,further researches have   
shown that the conditions which rule the
 development of the root-system and     
root-hairs in the soil are very complex1
 and not always easy to trace4 ,the most
 general statements we can make are the 
following3  ,there is an optimum degree 
of moisture in the soil which promotes  
the maximum development of root-hairs4  
,if the soil is too wet they are not    
developed4  ,these facts are of         
importance as correlated with the ease  
or difficulty experienced by the roots  
in obtaining water1 and plants such as  
our ordinary agricultural plants show   
this very distinctly4  ,although1 as    
shown in the experiments with wheat1 the
 short roots in dry soil were more      
densely covered with root-hairs than the
 much longer roots in moderately moist  
soil1 subsequent closer investigation   
shows that the total quantity and area  
of root-hairs is less in the former case

 than in the latter4  ,the greatest     
number of root-hairs are developed on   
roots which are growing at their best3  
too much moisture may prevent the       
formation of root-hairs3 too little may 
induce dense growths of root-hairs      
locally1 but the total number is        
reduced4  ,another set of events which  
exerts influence on the development of  
root-hairs is the composition of the    
dilute solution--water containing       
dissolved salts--which surrounds them in
 the soil4  ,thus1 ,schwarz found that  
when similar oat and wheat plants were  
grown with their roots in solutions of  
various salts1 the results differed as  
follows3  ,oats in a #ae per cent4      
solution of calcium chloride developed  
no root-hairs1 though they formed in a  
#e per cent4 solution1 and were very    
numerous in a #j4e per cent4 solution1  
or in water alone4 ,in a #aj per cent4  
nutritive solution the plants developed 
no root-hairs1 though they were abundant
 in a #a per cent4 solution4  ,wheat    

plants with their roots in a #ae per    
cent4 solution of potassium nitrate bore
 no root-hairs1 but they were numerous  
in a #b per cent4 solution of the same  
salt4  ,these are extreme cases1 for1   
although the roots were not killed1 they
 were strongly inhibited in their growth
 by the more concentrated solutions4    
,however1 experiments of this kind at   
least bring vividly before us what      
variations are possible1 and suggest    
that similar events on a smaller scale  
may occur in a soil which yields large  
quantities of soluble substances1 e4g4  
when freshly manured4 ,obviously these  
facts have a practical significance as  
regards kind of soil1 drainage1 season  
7e4g4 drought or wet71 etc4  ,but there 
are other factors which rule the        
development of root-hairs1 and some     
experiments by ,lesage show that the    
correlations between the development of 
root-hairs and roots are probably much  
more complex than had been suspected2   
for he finds that if the lateral        

rootlets of a ,bean1 in a water culture1
 are suppressed1 the main rootlet       
develops numerous and very long hairs to
 compensate the loss in surface1 a      
matter of obvious importance in the     
discussion of cases where roots have    
been injured in the soil4  ,before      
proceeding further it is necessary to   
look a little more closely into the     
structure of a single hair4  ,it is a   
tubular prolongation of a single cell of
 the external covering of the young     
root1 usually about #a to #c mm4 in     
length1 and #j4ja to #j4aj mm4 in       
diameter4 ,in special cases the         
root-hairs of some water plants may     
reach #e to #ah mm4 in length1 but of   
course ,i am referring to the ordinary  
land plants of agriculture and forestry4
 ,this tubular prolongation is closed   
and rounded off at the distal free end1 
and opens at the proximal end into the  
cell of which it is a protrusion4  ,the 
whole structure is bounded by an        
extremely delicate and elastic wall of  

cellulose1 which ,frank says is of      
special composition1 almost too thin to 
measure in many cases1 but often        
somewhere near #j4jje to #j4jja mm4 in  
thickness4 ,this thin membrane is       
remarkably permeable by water1 or dilute
 solutions1 as is shown by the rapidity 
with which a root-hair collapses if     
exposed to evaporation1 or with which   
dense solutions abstract water from it1 
or with which solutions may be seen to  
penetrate it under the microscope4      
,overlying the thin cell-wall proper1 on
 the outside1 is a thin gelatinous      
layer1 a product of alteration of the   
outermost lamellae of the former4       
,closely lining the proper cell-wall on 
the inside1 is an extremely thin layer  
of living protoplasm1 and somewhere in  
this protoplasm is a distinct           
cell-nucleus4  ,the interior of the tube
 is filled with cell-sap1 and it is the 
osmotic pressure of this cell-sap which 
keeps the whole living instrument tense 
and rigid1 and the thin protoplasmic    

film close pressed against the cellulose
 cell-wall4  ,nothing whatever can pass 
into the cell-sap1 or out from it1      
without traversing both the lining of   
living protoplasm and the cell-wall4    
,if we gently pull a living root1 of    
wheat1 pea1 mustard1 etc41 from a normal
 soil1 we find particles of soil so     
closely adherent to the root-hairs that 
they cannot all be washed off without   
tearing the hairs3 the root-hairs       
establish relations of contact with     
these particles1 so close that they are 
cemented to the solid surfaces by means 
of the gelatinous layer already referred
 to4 ,this peculiarity has the following
 consequences4 ,in the first place1 the 
enormous holdfast1 ensured by the       
millions of points of adherence1 enables
 the plant to withstand even powerful   
lever actions from above1 and provides  
fixed points against which the root-tips
 can work as they drive deeper into the 
soil4 ,in the second place1 the intimate
 contact of the root-hairs and particles

 of soil1 ensures that the films of     
water held by surface-action on the     
soil-particles and root-hairs shall be  
in continuity with the water saturating 
the cell-walls of the latter1 and       
therefore with the protoplasm and       
cell-sap in their interior4 ,the        
importance of this at periods when the  
soil is dry will be obvious1 when we    
reflect that no soil is ever naturally  
so dry that surface-films of water are  
absent from the particles4  ,the fact   
that the root-hair contains living      
protoplasm1 enables us to understand to 
a certain extent the results of the     
following experiments4  ,if we have a   
leafy and healthy plant1 with roots1    
bearing numerous root-hairs1 properly   
established in suitably moist soil in   
the pot1 the roots cease to absorb water
 if the temperature of the soil falls   
below a certain minimum1 though they    
recommence to do so if the temperature  
is raised again3 this has nothing to do 
with the temperature of the upper parts 

of the plant1 or of the air1 and the    
latter may be so high that the plant    
rapidly droops from loss of water at the
 leaves1 which is not being compensated 
owing to the inactivity of the roots4   
,similarly we may have the air so cold1 
at a time when the soil is warm enough  
to keep the root-hairs actively at work1
 that the plant becomes surcharged with 
water1 which escapes from the leaves    
like drops of dew4 ,the temperatures    
necessary to cause these disturbances in
 the action of the living root-hairs    
vary for different plants1 and even for 
different varieties of the same species4
  ,similar arrestation of the functions 
of the roots may be brought about by    
removing the oxygen from the soil around
 the root-hairs1 and replacing it by    
carbon-dioxide1 or the vapour of        
chloroform4 ,if not kept too long in    
such a condition1 the plant recovers    
rapidly on admitting atmospheric oxygen1
 which is always present in a normal    
well-drained soil both as gas in the    

capillary interspaces1 and dissolved in 
the water on the surfaces of the        
particles4 ,if the access of oxygen is  
delayed1 however1 as often happens in   
rainy seasons and in wet soils1 the     
root-hairs are killed1 and rot sets in4 
,a good instance of this has lately been
 given by ,heinricher in the case of    
potatoes4   ,,notes ,,on ,,chapter ,v4  
,for the further pursuit of this subject
 the reader should      consult ,sachs' 
,lectures1 ,,ii4 and ,,xv42 ,sorauer1 ,a
 ,popular      ,treatise on the         
,physiology of ,plants1 #ahie1 chapters 
,,ii4 and      ,,iv41 and ,pfeffer's    
,physiology1 pp4 #adi-afc4 ,the         
principal      paper on root-hairs      
referred to in the text is ,schwarz1    
,die      ,wurzelhaare der ,pflanzen1 in
 ,unters4 aus dem bot4 ,inst4 zu        
,wuerzburg1 ,i4 ,heft #b1 #ahhc1 p4     
#adj1 where a very exhaustive           
account of these organs will be found4  
,,chapter ,,vi4  ,,the ,,functions ,,of 
,,root-,,hairs4       ,excretions from  

root-hairs--,osmotic                    
phenomena--,turgescence--               
,plasmolysis--,control of the protoplasm
 in absorption1 etc4      ,selective    
absorption4   ,we see then that the     
root-hairs are the active living        
instruments in absorbing the water      
7containing small quantities of         
dissolved substances7 of the soil4  ,if 
the living root-hairs are so numerous   
and so active1 however1 a natural       
inference is that they must exert some  
influence on the composition or         
arrangement of their environment4 ,all  
the teachings of modern physiology go to
 show that such a living cell as ,i have
 sketched cannot carry on its life1     
brief though it be--the root-hairs are  
active for about four or five           
days--without forming substances of the 
nature of excreta1 and we should expect 
some of these to pass out to the soil4  
,sachs showed1 in #ahfj1 that roots     
growing in contact with polished marble 
corrode the surface of the mineral1 and 

,nobbe1 in #ahgf1 showed that the roots 
of seedlings reduce potassium           
permanganate1 a fact which ,molisch     
confirmed in #ahhg4 ,the latter observer
 also proved that living root-hairs     
secrete substances which colour a       
solution of guaiacum blue1 oxidise      
pyrogallic acid and other organic       
substances1 and rendered it probable    
that they excrete some substance which  
inverts cane-sugar1 and in some cases   
even small quantities of a diastatic    
enzyme4  ,molisch also confirmed an old 
observation1 that roots excrete         
carbon-dioxide2 and he and ,czapek      
showed that the root-hairs excrete acids
 more permanent in their nature than    
carbonic acid1 and published a method   
for showing this by means of a dilute   
solution1 slightly alkaline1 of         
phenolphthalein4  ,molisch declared that
 the substances secreted by root-hairs  
may even be observed1 dissolved in drops
 which ooze from the surfaces of the    
root-hairs4  ,that these                

root-excretions1 and particularly the   
acids1 may be of service in dissolving  
and rendering more available various    
constituents of the soil is an obvious  
suggestion1 and it is borne out by      
,sachs' discovery of the corrosion of   
marble1 and by ,molisch's observation   
that living roots slowly corrode ivory  
if continuously kept in contact with it4
  ,but a deeper insight into the        
physiology of these organs was only     
possible when the meaning of the        
phenomena of osmosis had been rendered  
clearer by the researches of ,pfeffer   
and ,de ,vries in #ahgg4  ,de ,vries    
showed that the turgescence of the      
living cell can be diminished1 and even 
reduced to nothing1 by placing the cell 
in contact with solutions of substances 
which attract water from the cell-sap3  
as the turgescence diminishes1 the cell 
contracts1 owing to the elasticity of   
the cell-wall1 which was previously     
distended2 if the abstraction of water  
continues1 the living protoplasmic      

membrane lining the cell-wall contracts 
away from the latter4 ,he then proved   
that no injury need accrue to the cell  
by this process of plasmolysis1 since   
the turgescence can be restored by      
washing out the salt with a more dilute 
solution1 or with pure water2 and the   
cell may go on living and even growing  
as before4 ,these phenomena can only be 
produced in cells where the protoplasmic
 lining is intact and alive4  ,pfeffer  
showed that the whole matter depends on 
the properties of the living            
protoplasmic membrane1 which1 so long as
 it is alive1 has the power of governing
 the entrance or exit of dissolved      
substances1 but is as a rule freely     
permeable for water4 ,if1 then1         
substances with a powerful attraction   
for water are formed in the cell cavity1
 and of such a nature that the          
protoplasm does not permit their free   
diffusion to the exterior1 they attract 
water1 and hold it fast1 and so set up  
the condition of hydrostatic pressure   

known as turgescence1 the limit of which
 depends on the attainment of a state of
 equilibrium between the elastic        
reaction of the cell-wall and the       
distending power of the absorbed water4 
,when this limit is reached1 water      
begins to filter back again through the 
cell-wall4 ,numerous researches during  
the last fifteen years have shown that  
the sap of such a living cell as the    
root-hair is charged with substances of 
various degrees of osmotic power2 bodies
 like sugars1 amides1 vegetable acids   
and their salts1 being formed by the    
metabolic activity of the protoplasm and
 accumulated there4 ,moreover1 we now   
know that the salts of the vegetable    
acids in particular are effective1 and  
the researches of ,warburg and ,palladin
 in #ahhf have placed it beyond         
reasonable doubt that these acids are   
continually being developed and         
destroyed in the living cell during     
normal growth and respiration1 and that 
great variations as to quantity may be  

brought about by alterations in the     
conditions of the environment--e4g4     
temperature1 oxygen1 etc4  ,if1 now1 we 
bring a solution of some salt1 such as  
potassium nitrate1 which has a powerful 
attraction for water1 on the outside of 
the living root-hair1 the question      
whether the water remains in the cell1  
or passes out of it1 merely depends on  
whether the substances inside or that   
outside have the most powerful          
attraction on the water in the sap1     
since the protoplasm allows water to    
pass freely4  ,but the protoplasmic     
lining may affect the whole matter in   
another way2 for it may allow the       
dissolved salt1 or other substance1 in  
the solution outside or inside the cell 
to pass through it also1 or it may take 
it up and fix it1 or break it up or     
otherwise alter it4  ,more recent       
researches1 and especially those of     
,pfeffer1 have shown that these         
diosmotic properties of the living      
protoplasm are of the utmost importance 

in the whole matter of absorption of    
substances from the soil4  ,let us      
suppose the following case4 ,a          
root-hair1 in full vigour1 is allowed to
 bathe freely in a dilute solution of   
various substances1 such as sugar1      
potassium nitrate1 phosphates1 sulphates
 and carbonates of iron1 soda1 lime1    
magnesium and others known by experiment
 to be harmless to its life4  ,now it   
turns out to be by no means a foregone  
conclusion that all or any of the       
substances1 even though freely soluble  
in the water1 can pass through the      
protoplasm into the interior of the     
cell4 ,some may be allowed easy access1 
others may only be permitted to pass in 
small quantities1 and others1 again1 may
 be absolutely refused access by the    
delicate living filter1 so long as it is
 vigorously alive4 ,nor1 as proved by   
numerous experimental cultures since ,de
 ,saussure's time1 is the entrance of a 
salt1 etc41 ruled by its                
indispensability or otherwise in the    

economy of the plant4 ,and it is        
important to notice that only experiment
 can prove the point and determine which
 substances are absorbed and which      
refused by the root-hair4  ,if we now   
suppose the protoplasm to give rise to  
powerfully osmotic substances which     
accumulate in the sap-vacuole1 but which
 are not permitted free egress through  
the protoplasm 7and the formation of    
such bodies will occur if the protoplasm
 is actively respiring71 the conditions 
for absorption of water1 with or without
 any dissolved salts1 which the         
protoplasm allows to traverse it1 are   
set up4  ,but the above supposed case is
 realised1 as ,pfeffer showed in #ahhf1 
when he found by a series of beautiful  
experiments that certain aniline dyes   
can accumulate in living root-hairs1 and
 other living cells1 whereas others     
cannot pass the living protoplasm4      
,after accumulating for some time1 the  
dye may either remain stored there1 or  
may eventually diffuse out4  ,pfeffer   

made another discovery1 of equal        
importance1 namely1 that under the      
influence of dilute organic acids1 such 
as citric acid1 the permeability of the 
living protoplasm may be altered1 so    
that it allows substances to pass which 
could not otherwise have traversed it4  
,de ,vries had also shown that the      
condition of the protoplasm affects its 
power of retaining the colouring matter 
in the sap of the ,beet3 so long as the 
protoplasm is alive1 the crimson sap is 
retained1 even when the cell is         
plasmolysed1 but immediately it begins  
to die the colour escapes through it4 ,a
 similar case exists when the           
chlorophyll-corpuscles retain their     
colour in living cells known to be      
charged with acids3 so long as the      
protoplasm is alive and normally active 
the green bodies are protected4  ,these1
 and numerous other experiments of the  
same kind1 prove that the healthy       
root-hair is a living instrument for    
taking up dilute solutions out of the   

soil1 and holding them in the sap-cavity
 for a time4 ,if killed1 by frost for   
instance1 it loses these powers4  ,the  
researches of the last ten years have   
also shown that a time comes when the   
turgid cell1 if an isolated one1 and if 
sufficient supplies of water are        
present1 is so tightly distended that   
the surplus water begins to diffuse out 
again under the pressure proper to the  
hydrostatic conditions set up4  ,now we 
arrive at a very critical point4  ,when 
the water1 or dilute solution of various
 substances1 begins to exude under      
pressure from the living root-hair1 what
 is to prevent its escape into the soil8
 ,and if it thus diffuses out1 where is 
the object of absorption8  ,the         
questions are obviously pertinent1 and  
they may seem the more so in that the   
cells adjoining the root-hair on its    
inner side are also turgid1 and possess 
similar properties to those of the      
root-hairs4 ,to establish a condition of
 things which shall bring about the     

inward flow of the absorbed water1 one  
of the three following cases is         
conceivable4 7#a7 ,the cells1 as we pass
 radially into the root1 have different 
properties on the wall of the two sides2
 or 7#b7 they are more and more greedy  
of water owing to some process of       
extraction of their water by tissues in 
the centre of the root2 or 7#c7 these   
successive series of cells possess      
osmotically more powerful contents at   
periods coincident with the escape of   
the water from the now osmotically      
weaker root-hairs4  ,a little reflection
 will show that where we have a group of
 such cells as the above1 all capable of
 absorbing water and dilute solutions   
and of becoming turgid1 movements of the
 absorbed water must go on until all the
 cells are in equilibrium1 as regards   
their osmotic pressures4  ,now the      
living rootlet is just such a system1   
the various cells of which are in       
different conditions of osmotic pressure
 at any given time3 some of these cells 

are old1 and their protoplasm is        
allowing sap to filter out under        
pressure3 others are in the height of   
their vigour1 and their protoplasm      
extremely impervious to the highly      
osmotic sap-constituents which it itself
 is forming actively3 others are too    
young to have attained their full       
turgescence3 while others again are in  
stages intermediate between the above4  
,there is another point of importance1  
however1 to explain some peculiarities  
in the absorption of these dilute       
solutions of salts1 etc41 by the        
root-hairs from the soil1 and by cells  
lying deeper in the plant from these    
root-hairs4  ,it is easy to understand  
that if a root-hair absorbs a given     
substance--say calcium sulphate1 for    
illustration--and hands it over to other
 cells unchanged1 a time must be        
supposed to arrive when1 the sap of all 
the cells being equally charged with    
calcium sulphate1 no more could be      
absorbed3 the rate of absorption of this

 particular substance1 and the quantity 
absorbed1 up to the hypothetical point  
of equilibrium chosen1 would then depend
 simply on the ease with which its      
molecules traversed the living          
protoplasmic membrane1 and the degree of
 their solubility in the sap4  ,but now 
suppose the following new factor to come
 in4 ,suppose that calcium sulphate     
undergoes decomposition in some one of  
the internal cells of the system of     
absorbing cells1 or that it is even     
merely crystallised out in such a cell1 
or in any other way removed from        
solution 7e4g4 by deposition in         
cell-walls74 ,this alters the state of  
affairs considerably4 ,the separation of
 the molecules from the sap-solution is 
itself a cause for the flow of more of  
the solution to the cell concerned1 and 
such causes of diffusion are very common
 in the plant4  ,the importance of this 
principle consists in that it lies at   
the base of the whole question of       
selective absorption1 application of    

manures1 and the rotation of crops2 and 
those who are acquainted with the       
excellent analytical results of ,de     
,saussure1 ,boussingault1 ,wolff1       
,trinchinetti1 ,goedechen1 etc41 and the
 water-culture experiments of ,sachs1   
,nobbe1 and others1 will understand what
 an illuminating effect on these points 
was produced by the above               
generalisation1 which we owe especially 
to ,pfeffer's splendid researches into  
the nature of osmotic phenomena4  ,it   
will now be clear1 ,i hope1 why we      
regard the living root-hairs as         
instruments--as pieces of living        
machinery--for the active absorption of 
water1 with substances dissolved in it1 
from the soil2 and it will also be      
evident1 ,i think1 that no one can form 
a proper conception of this matter of   
absorption1 so important in all         
agricultural questions1 unless he pays  
attention to these biological phenomena4
 ,it was hopeless to expect to          
understand these matters merely in the  

light of chemical analyses of plants and
 soils1 and one expression of this      
hopelessness was the belief in the power
 of roots to select only the substances 
useful to it4 ,we now know that the     
expression selective power of roots has 
a totally different meaning from that   
implied in the minds of the last        
generation of agriculturalists1 and it  
would be easy to devise experiments1    
with solutions of different strength1   
where the plant should be made to take  
up relatively large quantities of       
harmless1 but useless minerals1 etc41   
and to starve in the midst of plenty of 
the elements proper to its structure1   
simply because the former are offered in
 a form in which they easily traverse   
the protoplasm of the root-hairs1 while 
the latter are presented in a form      
unsuitable for absorption4 ,that all    
these matters are of importance in      
regard to manuring and choice of soils1 
etc41 needs no emphasising4  ,these     
remarks1 of course1 do not detract from 

the value of good comparative chemical  
analyses1 when viewed in the light of   
physiological knowledge1 as ,i need     
hardly say2 but they do1 and            
emphatically so1 attack the position    
that such analyses alone can explain the
 problems of agriculture4  ,on the other
 hand1 we must not rest satisfied with  
the suggestions so far put forward to   
account for the processes referred to1  
since it is impossible to overlook the  
fact that in their present form they    
merely afford proximate explanations1   
and are too crudely mechanical for      
finality4   ,,notes ,,on ,,chapter ,,vi4
       ,in addition to the works        
referred to in the last chapter1 the    
student should consult ,pfeffer's       
,physiology1 pp4 #hf-adi1 and      pp4  
#daj-dda4 ,with reference to water      
cultures1 ,sachs'      ,lectures1       
,,xvii41 may also be consulted4 ,the    
standard work on      ash constituents  
of plants is ,wolff1 ,aschen-analysen1  
#ahga      and #ahhj1 an indispensable  

book of reference in this               
connection1 though there are others1    
quoted in ,pfeffer1 where      further  
literature may also be found4           
,,chapter ,,vii4  ,,the ,,biology ,,of  
,,soil4       ,soil not a dead          
matrix--,organic materials--,the living 
organisms of the soil--,their           
activities--,their numbers and          
importance4 ,abandonment of the notion  
that chemical analysis      can explain 
the problem4   ,it is customary to      
regard the soil1 between the particles  
of which the root-hairs of plants are   
distributed1 as if it were merely a dead
 matrix of smaller or larger pieces of  
rock1 such as sand1 gravel1 stones1     
etc41 and organic remains1 such as bits 
of wood1 leaves1 bones1 etc41 with water
 and air in their interstices4 ,as      
matter of fact1 however1 soil is a much 
more complex body than was suspected    
until comparatively recent times4  ,it  
is1 of course1 beyond the scope of this 
book to go into the different varieties 

of soils1 their structure or            
arrangement1 and the chemical nature of 
their constituent rocks and the debris  
mingled with the latter4 ,for the same  
reason ,i must pass over the curious    
properties of soils in relation to the  
solutions they yield to water in        
contact1 the manner in which they retain
 some of these solutions and allow      
others to pass easily1 and the          
remarkable double decompositions which  
go on in them4 ,moreover1 ,i must assume
 as known the chief physical properties 
of ordinary soils with respect to the   
phenomena of capillarity1 absorption of 
heat1 action of frost1 and so forth4    
,but all ideas as to the nature of soil 
based merely on the study of its        
chemistry and physics are misleading1   
and it is in just the establishment of  
this truth that modern discoveries in   
,agricultural and ,forest ,botany have  
played so important a part4  ,from the  
facts that organic debris is found      
chiefly at the surface of the earth1 and

 that the smallest particles are held in
 suspension by the water near the       
surface1 it is comprehensible why such  
organic remains abound in the upper     
parts of the soil1 where the rootlets   
with their absorbing root-hairs are also
 found1 because they must have oxygen4  
,the rule is1 therefore1 that an        
ordinary soil consists of upper strata1 
rich in organic materials and in oxygen1
 and a subsoil1 poorer in these         
substances4  ,among these organic       
materials are countless myriads of      
living beings1 especially fungi and     
bacteria1 which require oxygen and      
organic materials for their subsistence1
 and it depends on the open or close1   
moderately moist or damp1 warm or cold  
nature of the soil1 and on some         
obviously connected factors1 how far    
down these aerobic organisms can thrive4
 ,as we go deeper down they become fewer
 and fewer1 and gradually disappear1 and
 7neglecting certain anaerobic bacteria 
of putrefaction7 they are rarely found  

in marked abundance more than a few     
inches below the surface soil4  ,these  
aerobic fungi and bacteria are the great
 agents of continued fertility of a     
soil1 and it is they which1 living and  
multiplying in the moist and            
well-aerated warm interstices of a rich 
open soil1 carry out the useful         
destruction of organic matter1 breaking 
it up into mineral and gaseous bodies1  
which are then dissolved in the water   
bathing the root-hairs or escape into   
the atmosphere4 ,in this work of        
destruction they are aided by the oxygen
 of the air and the solar heat3 their   
own fermentative action is also         
accompanied by a marked rise of         
temperature1 and the carbon-dioxide and 
other products of their activity all go 
to complicate the chemical changes going
 on in the soil around the roots4       
,duclaux has calculated that            
,aspergillus niger1 a common mould      
fungus1 can break down organic          
substances1 such as carbohydrates1 at   

such a rate that a metre cube of the    
fungus would decompose more than #cjjj  
kilogr4 of starch in a year1 and this   
may serve as an example giving some idea
 of the possibilities in soil4          
,analyses of waters containing large    
quantities of organic matter1 as they   
enter such open soils as those referred 
to1 compared with the drainage water    
after passing through the upper strata1 
show that the carbonaceous and          
nitrogenous materials are broken down to
 more or less completely oxidised       
simpler compounds1 and that the         
following chief changes result4 ,the    
ammonia and some other nitrogenous      
bodies remain behind in the soil1 as    
also do the phosphoric acid and much of 
the potash2 whereas large quantities of 
nitric and nitrous acids1 together with 
much sulphuric acid1 chlorides1 and     
calcium salts pass away in the drainage4
 ,these facts are obviously highly      
important in agriculture4  ,experiments 
on sewage farms have shown also that the

 upper soil retains most of the bacteria
 of the sewage4 ,koch found at ,osmont1 
near ,berlin1 that whereas the different
 sewage waters contained numbers so     
enormous that each cubic centimeter     
probably held #ch1jjj1jjj germs1 the    
different drainage waters held only     
#hg1jjj per c4cm42 and the whole process
 of water-filtration through sandy soils
 depends on these well-known facts4     
,recent experiments in connection with  
soil-filtration1 however1 bring out the 
further facts that the oxidations which 
organic matters undergo in the soil--and
 without which they are useless to the  
higher plants--are enormously enfeebled 
if the upper layers of soil are         
sterilised1 so as to deprive them of the
 myriads of aerobic bacteria1 fungi and 
yeasts which they normally contain1 and 
there can no longer be any doubt as to  
the importance of the biology of the    
soil in connection with the preparation 
of materials suitable for absorption in 
solution by the root-hairs of           

agricultural and other plants4  ,the    
researches of the last ten years have   
brought to light a long list of forms1  
comprising yeasts1 such as ,hansen's    
,saccharomyces apiculatus1 fungi and    
bacteria which live and grow in the     
soil1 finding their water and food      
supplies in the interstices1 and under  
conditions which we now know to be very 
diverse4 ,they are usually more         
numerous1 in species and individuals1 in
 cultivated farm and garden soils than  
in woods1 prairies1 and untilled lands2 
but the geological nature of the strata1
 the closeness and otherwise of the     
soil1 its damp or dry character and its 
average temperature 7which depends on   
many things besides latitude or         
altitude7 and other factors co-operate  
to rule their distribution and numbers4 
,the fact that cultivated land is so    
well supplied with manures1 air1 etc41  
is of great importance in relation to   
their relative abundance there1 and it  
is extremely probable that the use of   

artificial manures lessens their numbers
 considerably as compared with land on  
which stable and other animal manures   
are employed4  ,a list of the           
soil-bacteria which have been isolated  
and more or less carefully cultivated   
and examined would comprise about fifty 
species2 but it is certain that1 as at  
present classified and named1 many more 
species are to be discovered in any     
ordinary soil4  ,the fungi are          
apparently even more numerous than the  
bacteria1 and we may rest satisfied for 
the present with the general statement  
that the life-actions of the myriads of 
individuals of these organisms in the   
soil completely alter the question of   
soil-water as understood by the last    
generation of agriculturalists4  ,but   
there is another aspect of this question
 of soil-organisms which has grown in   
importance of late to such an extent    
that we are more than ever justified in 
regarding the biology of soil as far    
more vital to the interests of the plant

 than its physical or chemical          
properties4 ,with many of the fungi in  
the soil the roots of plants have to    
compete--just as plant competes with    
plant--for water1 salts1 and other      
food-materials4 ,the toadstools which   
are so conspicuous in fields and forests
 spring from mycelia which ramify in the
 ground1 and are busily breaking down   
the remains of other organisms1 and just
 such fungi are known to store up       
relatively large quantities of salts of 
potassium and phosphorus--the very salts
 which are so valuable to crops and     
occur so sparingly in most soils1 but   
which the extensively spread fungus     
mycelia can gradually accumulate4 ,some 
of these fungi1 moreover1 are more      
active in their antagonism1 and actually
 attack and pierce the roots as         
destructive parasites1 but ,i pass these
 by for the present1 as they form the   
subject for further consideration when  
we come to the diseases of plants4  ,it 
is obvious that the competition of fungi

 with root-hairs for mineral salts1     
oxygen1 etc41 may be at times acute1 and
 it is extremely probable that cases of 
so-called sterility of soil1 where a    
particular soil is found unsuitable for 
a crop1 may sometimes be due to this    
over-competition4  ,the researches of   
recent years1 however1 and especially   
those of ,frank1 ,winogradsky1          
,hellriegel1 and ,stahl1 have brought to
 light a series of relationships between
 certain of these soil-organisms and the
 higher plants which place the matter of
 soil-biology in quite new lights4  ,on 
the one hand it has been discovered that
 groups of bacteria are the active      
agents in bringing about the destruction
 of organic nitrogenous matter with the 
formation of ammonia1 in oxidising this 
ammonia to nitrous and to nitric acids1 
which combine with bases in the soil to 
form the corresponding salts2 while1 on 
the other hand1 other forms can         
decompose the nitrates and reduce them  
to nitrites1 or set free ammonia or even

 nitrogen from them4 ,moreover1 there   
are certain species which can fix the   
free nitrogen of the atmosphere1 and    
start the cycle of up-building of this  
inert element into the complex higher   
compounds we term organic4 ,it is       
impossible to over-estimate the         
importance of these processes of        
nitrification and denitrification going 
on in the soil about the root-hairs of  
the higher plants4  ,but1 in addition to
 this circulation of nitrogen in the    
soil1 it turns out that the life-actions
 of bacteria1 and not mere chemical     
decompositions1 are largely responsible 
for the circulation of carbon1 of iron1 
of sulphur and other elements formed    
from the decomposition--also by         
bacterial and fungal agency--of animal  
and vegetable remains in the soil4      
,even more startling are the biological 
relations in the soil between the       
absorbing roots of the higher plants and
 some of these bacteria and fungi1 for  
it has now been established beyond all  

doubt that certain fungi enter the      
living roots and there flourish not as  
mere destructive parasites1 but as      
messmates not only tolerated by the     
plant1 but even indispensable to its    
welfare4 ,it is probable that nearly    
half the plants of our fields1 moors1   
and forests entertain such fungi in     
their root-tissues4 ,the curious1 and   
long-known nodules on the roots of      
leguminous plants--peas1 beans1 clover1 
etc4--are filled with bacteria which    
enable these plants to avail themselves 
of the free nitrogen of the air1 and so 
enrich the soil with nitrogenous        
substances4  ,the roots of most forest  
trees1 orchids1 and plants of the       
moorlands1 meadows and marshes are      
similarly occupied by fungi1 which in   
some way convey salts--probably         
especially phosphates and potassium     
compounds--to the plant in return for   
the small tax of organic                
carbon-compounds it exacts from the     
latter4 ,in some cases at any rate1 as  

,bernard has lately shown1 the very     
existence of the plant depends on its   
seedling roots obtaining this           
advantageous attachment and co-operation
 7symbiosis7 of the fungus immediately  
on germination4  ,these remarks must    
suffice to illustrate this part of my   
subject1 and to emphasise the statement 
that the question whether a given plant 
can be grown in a given soil1 is by no  
means one of simply the physical and    
chemical constitution of the latter4    
,the plant will have to run the gauntlet
 of a long series of vicissitudes       
brought about by the presence or        
absence1 relative proportions and       
vigour1 and specific nature of the      
organisms in the soil at its roots1 and 
it is easy to see that many cases of    
disease may be due to the absence of    
advantageous bacteria or fungi1 or to   
circumstances which disfavour their     
life1 as well as to the predominance of 
competing organisms4  ,it will now be   
evident that the old points of view must

 be abandoned1 and with them1           
especially1 the widely prevalent notion 
that chemical analyses of the plant and 
soil can explain the real problems of   
agriculture4  ,it was of course an      
enormous advance in the science when1   
thanks to the splendid labours of the   
chemists1 at the end of the last century
 and the beginning of this1 we obtained 
that preliminary knowledge of the       
constitution of the air1 and of the     
composition of the water1 acids and     
salts1 etc41 which plants require for   
their food-materials and life-processes4
 ,much was gained by ,de ,saussure's    
establishment of the fact of oxygen     
respiration1 though we now understand by
 the term something very different from1
 and much more complex than1 what he    
understood by it1 as1 also1 much had    
been gained by the previously acquired  
knowledge of the gas-exchanges in       
carbon-assimilation3 nor must we forget 
the services of those who proved1 by    
laborious analyses1 continued for long  

periods1 what chemical compounds are    
found in the tissues of plants1 and in  
the soils at their roots and the        
atmosphere which surrounded them4 ,we   
must also remember many other           
contributions which have been furnished1
 and are still being furnished by the   
chemist2 and ,i for one hope that his   
labours will continue to go hand in hand
 with those of the physiologist4  ,but1 
when all due honour is paid to the      
scientific chemist1 it must still be    
allowed that his problems are different 
from the real problems of agriculture4  
,to take one set of instances alone4    
,the chemist can analyse a given soil or
 a given manure1 and can even go a long 
way towards making them1 but his        
analyses do not tell us what conditions 
are necessary in order that their       
ingredients may be presented to the     
roots so as to be absorbed and become   
built up into the plant4 ,chemistry told
 us that carbon was fixed from the air1 
but physiological experiments determined

 how this meant the synthesis of certain
 definite carbohydrates--this1 too1 in  
the face of the powerful authority of   
the chemist ,liebig1 who supposed that  
the vegetable acids were the results of 
the assimilation of carbon4 ,wolff1 ,de 
,saussure1 and other chemists have done 
yeoman service in showing that different
 plants1 growing in the same soil1      
contain different proportions of mineral
 substances2 but it was by means of     
water-cultures1 and other physiological 
researches1 such as those of ,pfeffer on
 osmotic phenomena and of ,schwarz and  
,molisch on root-hairs1 that the        
puzzling question of selective          
absorption1 by means of the living      
root-hairs1 came into the arena of our  
knowledge4  ,in every case--and1 as     
already said1 ,i am not undervaluing the
 work done--the chemist has left us only
 on the threshold of the real problem4  
,he has stood outside the factory in    
which the real work we want to know     
about is being carried on1 and has told 

us of so many tons of this material     
being carried in at the gates1 and of so
 many tons of that coming out2 he has   
even burnt down the factory1 and all its
 contents and machinery1 and has then   
told us how many tons of the various    
materials were there at the time2 but   
this is not what we want1 valuable as   
the information is1 and still more will 
be4 ,what we want1 and what we expect to
 obtain1 is more information regarding  
what is done with the materials in the  
factory3 what machinery they are put    
into1 and how they are put in3 what     
stages they go through1 and how the     
stages follow one another3 what wear and
 tear has to be endured1 and how we can 
step in and stop the working of the     
machine for our own benefit at the best 
possible time4  ,the physiologist       
proceeds empirically1 by experimenting  
with the living machinery4 ,he          
recognises the parts and their          
structure1 and tries to find out what   
they are doing3 he knows that the laws  

of physics and chemistry cannot be      
traversed1 but he sees these laws at    
work under special and very complex and 
peculiar conditions4 ,he therefore1 as  
the results of his experiments1 sets new
 questions--or old questions under new  
conditions1 if you like--and undoubtedly
 wants the help of both chemist and     
physicist2 or1 if it is preferred1 the  
chemist and physicist may attack the    
problems1 but they must familiarise     
themselves with the peculiar mechanism  
of the organism concerned1 and cannot   
hope to attain success without          
experimenting with it4 ,i confess it    
seems to me as reasonable to look upon  
scientific agriculture as a branch      
chiefly of chemistry as it would be to  
look upon horse-breeding or             
pigeon-rearing from the same point of   
view2 and why the professed chemist's   
advice is regarded as so comforting and 
final in the one case and not in the    
other is one of those mysteries which   
seem inherent in human nature4  ,the    

central point in agriculture is the     
plant3 get the most out of it--the      
energy-winning machine which alone can  
keep the animals and everything else    
connected with the farm going--and all  
the rest follows4 ,the old agriculture  
has taken a gloomy view of things1 and  
especially on account of a large        
variable which it blames for many ills1 
namely1 the season or climate4 ,perhaps 
the old agriculture has not sufficiently
 recognised that ,nature grows plants in
 accordance with the fact that variation
 is not peculiar to the weather3 if the 
seasons vary1 so do fruit and other     
produce and the plants which yield them2
 and since man cannot hope to control   
the one variable1 possibly relief will  
be found in doing more1 within his      
limits1 towards controlling others4  ,in
 any case he cannot hope to succeed     
without study of the physiology of the  
plant4   ,,notes ,,to ,,chapter ,,vii4  
,an admirable short account of soil in  
its relation to      root-hairs is given

 in ,sachs' ,lectures1 ,,xv42 but for a 
more      exhaustive treatment of the   
subject of soil the reader is           
referred to ,king1 ,the ,soil           
7,wisconsin1 #ahie71 or ,warrington1    
,lectures on the ,physical ,properties  
of ,soil 7,oxford1 #aijj72              
,larbaletrier1 ,l',agriculture 7,paris1 
#ahhh71 chapters ,,ii4 and      ,,iii4  
,there is also a very good account in   
,bailey1 ,the      ,principles of       
,agriculture 7,london1 #ahih71 chapters 
,i4-,,iii4       ,with reference to the 
organisms in soils and the              
decompositions they bring about1 the    
student should consult      ,kramer1    
,die ,bakteriologie in ihren            
,beziehungen zur      ,landwirthschaft  
7,wien1 #ahij71 and ,lafar1 ,technical  
,mycology      7,engl4 edition1 #ahih71 
sections ,v41 ,,viii41 and ,,ix4        
,,chapter ,,viii4  ,,hybridisation ,,and
 ,,selection4       ,the crossing of    
varieties of wheat1 etc4--,the          
essentials of                           

fertilisation--,rimpau's                
experiments--,hybrids and selected      
varieties4   ,in the more hopeful view  
of the case which the new agriculture   
will have to take1 it will recognise the
 physiological truth that since the     
living plant is the important and       
variable machine which constructs the   
produce looked for1 and since that      
machine will work best in proportion as 
its needs are properly satisfied2       
therefore in cases where the needs of a 
given type of the machine cannot be     
efficiently provided for1 it will be    
well to select some other type which    
will take what supplies and conditions  
can be offered4 ,of course1 this is     
already recognised to a certain extent1 
as is implied in the practices of       
rotation of crops1 selection of pedigree
 wheats and mixtures of pasture grasses1
 and in decisions as to the quality of  
land according to the kinds of weeds    
found on it1 and so forth2 but ,i am    
convinced that the agriculturist of the 

future--and the same applies to the     
horticulturist1 planter and             
forester--will have to concern himself  
more systematically with the working and
 the variability of the plant1 and      
particularly with what ,darwin termed   
,variation under ,domestication1 than   
has always been the custom in the past4 
,the subject of the plasticity of       
cultivated plants1 and especially of    
hybrids1 is in one sense an old one2 but
 much work is being done which proves1  
as such work is apt to do1 that very    
much more may be done by well-planned   
experiments on the selection of new     
varieties raised by hybridising and     
cultivation4  ,in illustration of this  
point1 a short summary of some of the   
results of crossing different species of
 wheat1 barley1 oats1 peas1 beet1 etc41 
may serve to show what has been gained  
and what may be hoped for in these      
directions4 ,it should be stated that   
much has been done and is being done in 
this country as well as abroad1 as      

witness ,english varieties of corn1     
peas1 and potatoes1 and the recent      
experiments on crossing various kinds of
 maize in ,america4  ,the hybridiser    
grows his cereals1 etc41 in pots until  
ready for crossing1 and then takes them 
into the laboratory1 removes the weaker 
spikelets1 and takes out the young      
stamens from the flowers left on the    
plant4 ,the female plant is then ready1 
and the flowers covered with paper caps4
 ,the pollen1 obtained by a clean wet   
brush from the plant chosen as the      
father1 is then carefully placed in     
position on the stigmas1 and the caps   
replaced4 ,the pollination is repeated  
occasionally1 and care taken that no    
uncrossed flowers develop later4 ,in    
this way a few seeds or grains are got  
to start with4  ,this would be the place
 to introduce an account of the enormous
 advances made by the botanists of the  
last decade or two in the study of the  
microscopic phenomena of fertilisation4 
,without going into details--which would

 more than occupy all the space at      
command--,i may recall the discoveries  
of ,strasburger and his pupils1 and of  
,guignard1 which have supplemented the  
earlier discoveries of ,de ,bary1 ,cohn1
 and ,hofmeister1 by establishing the   
facts that the essential point in       
fertilisation is the fusion of two      
nuclei1 and the bringing together in the
 fused mass of two extremely minute     
thread-like coiled bodies1 the so-called
 chromatosomes or filaments1 one of     
which is derived from the male and the  
other from the female parent4 ,the      
particulars as to the marvellous        
adaptations to secure the union of these
 two infinitesimally minute threads1    
their behaviour immediately before and  
after union1 and many other points must 
be passed over1 as ,i have only space to
 emphasise the one crowning discovery   
that these tiny filaments of nuclear    
substance are the material carriers of  
all the hereditary properties of the    
parents to the young plant which their  

union initiates4  ,it must not be       
supposed that the above statements are  
based on any meagre foundation of facts4
 ,the attraction of the fusing nucleated
 masses had been demonstrated over and  
over again by ,tulasne1 ,de ,bary1      
,strasburger and others2 but ,pfeffer   
brought the matter to a crisis by       
discovering the attractive 7chemotactic7
 substance emitted in given cases1 and  
by collecting the fertilising bodies by 
its means into artificial tubes4  ,the  
fusion of the nucleated bodies in the   
sexual act was observed by ,strasburger 
in the living plant a few years ago1 and
 numerous later observers have confirmed
 it4 ,meanwhile all the stages of       
approach and contact of the essential   
filaments of the nuclear substance have 
been traced1 as also all the stages of  
the transference of half of each        
filament1 male and female1 into each of 
the first two cells of the very young   
embryo-plant4  ,moreover1 the essentials
 are found to be the same in the animal 

kingdom also1 and the bearing of all    
these discoveries on the phenomena of   
reproduction1 variation1 and heredity in
 living organisms has been and is of the
 highest importance1 for they support1  
control1 explain and correct so many of 
the splendid results of ,knight1        
,koelreuter1 ,sprengel1 ,hildebrand and 
,hermann ,mueller1 and in every         
direction throw side-lights into the    
crevices of that magnificent structure1 
the theory of ,natural ,selection1      
erected for all time by our countryman1 
,charles ,darwin4  ,to return now to    
experiments on crossing4 ,it is found   
that the first products of the crossing 
appear exactly alike2 they may have     
characters intermediate between those of
 the father and mother1 or they may     
resemble one more than the other1 but   
all the seeds of the same cross do it in
 the same way4  ,on then sowing the     
seeds of the plants produced from this  
first cross1 variations begin to appear4
 ,most of the progeny revert to one or  

other of the parent forms1 others show  
all conceivable combinations of their   
characters1 and a few may give rise to  
entirely new characters4 ,in succeeding 
generations the reversions are          
preponderant1 and1 supposing no care is 
taken to prevent it1 the whole of the   
offspring gradually go back to the      
ancestral type4  ,some important        
consequences result1 however1 if        
systematic care is brought to bear on   
the matter4 ,this tendency to variation 
in the second generation of crossed     
plants has often been noted1 and it     
bears out very distinctly the           
conclusions to which ,darwin came4  ,the
 hybridiser takes advantage of this     
variation1 as others have done1 to      
select some forms and rigidly suppress  
others1 in order to obtain well-marked  
varieties of the plants he experiments  
with4 ,in illustration1 ,i may take the 
following from ,rimpau's account of his 
experiments on crossing wheat3 ,by      
crossing a white ,english long-eared1   

dense wheat1 and celebrated as a heavy  
cropper1 with a red1 looser ,german     
wheat1 remarkable for its resistance to 
winter cold1 ,rimpau hoped to obtain a  
variety uniting both the above          
qualities4 ,as regards the property of  
resistance1 he failed1 and he eventually
 gave up the attempts in face of the    
advantages offered by the so-called     
,square-heads1 which then came into the 
market4 ,his experiments1 even with the 
above varieties1 are worth noting1      
however1 for they show how promising the
 results of carefully conducted crossing
 and selection may be4  ,the crossing   
was done in #ahge1 in both directions4  
,in #ahgf the few grains obtained were  
found to yield plants almost all alike1 
with the long loose ear of the ,german  
parent1 but the paler colour of the     
,english wheat4  ,in #ahgg the plants1  
obtained by sowing the finest grains1   
were found to consist of pure white1    
pure red1 and of forms which appeared to
 vary and revert in all possible degrees

 as regards colour1 density1 and other  
characters intermediate between these4  
,by carefully separating the closest and
 densest white wheats from the closest  
and densest red ones1 he got in #ahgh a 
large number of each coming nearer to   
the type sown than did the mongrel forms
 intermingled with them3 these          
reversions and intermediate forms were  
then rigidly eliminated1 and only the   
deepest coloured and densest red and    
white forms again sown4  ,in #ahgi these
 two chosen varieties were constant1 so 
far as concerned those selected from the
 crossing of female ,english white with 
male ,german red wheat1 and the         
following year proved the constancy of  
the red variety in the reciprocal cross4
 ,in #ahhf all four varieties--i4e4 the 
two reds and the two whites of both the 
crossings--had become constant4  ,still 
more instructive are the results of the 
cross between the same white ,english   
non-bearded wheat and a red ,german     
bearded wheat4  ,the first results of   

the crossing in #ahge showed the loose  
ear of the ,german mother1 but was paler
 in colour2 while the influence of the  
,english father was shown by the absence
 of beard4  ,from the reversions and    
mixtures of the mongrels showing        
reminiscences of the parents in all     
degrees in #ahgg1 rigid selections and  
re-sowings were made as before1 and     
,rimpau eventually got four very        
distinct varieties1 two red and two     
white1 a bearded and a beardless form of
 each1 and these were declared fixed and
 constant in #ahgi-ahhb4  ,passing over 
many similar results1 and merely noting 
a very successful variety got from a    
cross between a very early ripening     
loose red ,american wheat and the dense 
heavy cropping ,english                 
,square-head--the crossed variety which 
has proved very suitable for certain    
light soils and dry climates on the     
,continent1 which demand very rapid     
ripening1 and are therefore of great    
physiological and technical interest--,i

 must pass on to note the curious result
 of the successful hybridisation of     
wheat and rye4 ,this cross has been     
effected several times1 and first in    
this country according to reports from  
,edinburgh 7#ahge71 ,new ,york 7#ahhf71 
and elsewhere1 and ,rimpau's careful    
experiments seem to leave no doubt on   
the matter4  ,first ,i must remind you  
that wheat 7,triticum7 differs from rye 
7,secale7 in several marked characters1 
such as the breadth and shape of the    
glumes1 the number of flowers in the    
spikelet1 etc42 and that the cultivated 
rye differs from cultivated wheats in   
the characters of the straw1 in having  
long ears1 and in its flowering glumes  
remaining widely divaricated for some   
days when in flower4  ,in #ahhh ,rimpau 
removed the young stamens from the      
,german wheat referred to1 and          
pollinated the stigmas with pollen from 
a long-eared rye4 ,four sound grains    
were obtained1 looking like             
wheat-grains4  ,the history of one of   

these grains was as follows3 ,in #ahhi  
it yielded ears which were peculiarly   
narrow and long1 and its stalks were    
also much longer than the wheat3 the    
flowers remained exposed1 with widely   
open paleae1 for several days1 and the  
grains were very peculiar1 though       
wheat-like4  ,fifteen of the best grains
 were selected1 and in #ahij three of   
the resulting plants proved to be a     
wheat of the ,square-head type and one  
quite sterile4 ,the others retained the 
elongated1 narrow1 brownish-red ears1   
the flowering glumes again opening wide 
for some days4 ,this last is a          
characteristic of rye1 but not of wheat4
  ,a long series of natural hybrids of  
wheat1 barley1 and oats are also        
described and discussed by ,rimpau1 as  
well as artificial crosses--some very   
remarkable--of barleys1 but they must be
 passed over here4  ,peas rarely become 
hybridised naturally4 ,according to     
,darwin1 ,h4 ,mueller1 and ,focke1 the  
flowers are little visited by insects in

 our countries1 though the mechanism    
points to their adaptation for          
pollination by large bees4  ,rimpau     
confirms ,darwin1 ,h4 ,mueller1 and     
,ogle as to the self-fertilisation of   
our cultivated peas4 ,nevertheless1 as  
is well known1 marked varieties have    
been obtained by artificial crossing by 
,gaertner1 ,knight1 ,laxton1 and others1
 especially in this country4  ,at the   
same time experiments show that while it
 is very easy to obtain artificial      
hybrids of such plants1 and there is no 
fear of natural inter-crossing1 the     
forms are remarkably unstable as yet4   
,similarly unsatisfactory results were  
obtained with beet4 ,as experiments are 
still going on1 however1 we may expect  
to hear more about these and other      
results4  ,it is probable1 from recent  
experiments by ,de ,vries1 ,correns1 and
 others1 that a remarkable regularity1  
expressed by ,mendel in the form of a   
law1 obtains in the variations which    
result from hybridising4  ,in           

considering these illustrative cases1 it
 is necessary to thoroughly apprehend   
that two procedures are involved4 ,in   
the first place we have the             
cross-pollination leading to the        
formation of the hybrid plant by        
cross-fertilisation4 ,but experience    
shows that this would lead to very      
uncertain results if the plant-breeder  
did not supplement them by the second   
and extremely important process of rigid
 selection--i4e4 by choosing the best of
 the progeny and breeding from them     
apart from the parent-forms1 and        
gradually intensifying1 as it were1 the 
variations in certain directions which  
have been started by the crossing4  ,it 
is by selection1 careful culture1 and   
repeated selection that so much has been
 done in obtaining the innumerable new  
varieties of roses1 sweet-peas1 orchids1
 orchard fruits1 cereals1 grapes1       
strawberries1 melons1 tomatoes1 early   
potatoes1 etc41 brought forward by      
numerous breeders of plants in all      

countries1 as will readily be understood
 if reference be made to the work of    
,hays and ,webber in ,america2 ,saunders
 in ,canada2 ,garton1 ,sutton1 ,veitch1 
,bateson1 and others in this country4   
,nor is it necessary that the new       
materials for selection to work upon    
should be started by hybridisation4     
,grafting1 change of conditions1 and    
even variations so vaguely understood   
that we term them spontaneous1 may      
supply the starting-points for changes  
in the characters of plants1 so         
remarkable after intensification by     
breeding that people find it difficult  
to believe they can have come from one  
stock4  ,here1 however1 ,i must         
conclude1 merely remarking that the     
above sketch is a mere outline of the   
subjects modern agriculture and         
horticulture concern themselves with4   
,there are hundreds of problems         
connected with the germination of seeds1
 on which valuable recent work has been 
done by ,klebs1 ,green1 ,horace ,brown1 

and others2 with the resistance of seeds
 and seedlings to high and low          
temperatures1 a subject opened out by   
,sachs1 ,kny1 ,de ,vries1 ,krasan1      
,just1 ,hoehnel1 ,dewar1 ,dyer1 and     
others2 with the conditions of          
vegetation which affect the various     
functions of growth1 respiration1       
assimilation1 transpiration1 and so     
forth1 on which ,i cannot even touch in 
these pages4  ,meanwhile ,i hope ,i have
 succeeded in impressing upon you the   
grand fact that the plant is a living   
and very complex engine1 driven by the  
radiant energy of the sun1 and capable  
of doing work thereby1 and this just as 
truly as any heat-engine is driven by   
chemical energy gained by means of the  
sun's rays1 or as a water-mill is driven
 by power which must be referred to the 
energy of potential in the head of water
 placed in position by the sun's work in
 evaporation4 ,fundamentally the whole  
of life and work on our planet is to be 
referred to the one great source of     

energy which renders possible the       
establishment of differences of         
potential4  ,this machine1 then1 doing  
work in various ways1 adapts itself--or 
goes to the wall--to the conditions of  
its work among competing organisms or   
opposing circumstances4 ,curiously      
enough1 while in some cases it suffers  
from the competition1 in others it is   
benefited by its life-actions fitting in
 between those of other organisms1 which
 in their turn supplement it4 ,in other 
words new types of this engine1 capable 
of doing the work in various ways1 are  
obtainable2 some are good types for the 
conditions afforded1 others are bad     
ones4  ,examples of both will occur in  
the further exposition of the subject4  
,man's position in regard to the        
struggle is that of an intelligent being
 who steps in at certain stages and     
protects1 fosters1 and in every way     
favours the agricultural plant--the     
living machine--and sees that every     
opportunity is given it to do its best  

work in the best way--from his points of
 view6   ,,notes ,,to ,,chapter ,,viii4 
,the foundation of any course of reading
 on hybridisation      and selection    
should be ,darwin's ,effects of ,cross  
and      ,self-,fertilisation in the    
,vegetable ,kingdom1 which1 with his    
books ,on the ,origin of ,species by    
means of ,natural ,selection      and   
,the ,variation of ,animals and ,plants 
under ,domestication1      will prepare 
the student for the long course of      
reading      necessary for a full       
appreciation of what has been done in   
this department of science4       ,from 
the numerous works which followed these 
,i should select      ,bailey's         
,survival of the ,unlike1 ,london1      
#ahif1 and      ,evolution of our       
,native ,fruits1 ,new ,york1 #ahih1 as  
especially useful for the reader of this
 book1 to which may      also be added  
,plant ,breeding1 ,new ,york1 #ahif1 by 
the same      author1 as giving numerous
 facts and practical directions of      

value4 ,further1 the ,hybrid ,conference
 ,report1 ,journ4 ,roy4      ,hort4     
,soc41 #aijj1 abounds in facts and      
information4 ,rimpau1      ,landw4      
,jahrb41 vol4 xx41 #ahia1 p4 #bci4 ,the 
student who      wishes to get towards  
the root of the matter will hardly be   
able to dispense with ,strasburger's    
,neue ,untersuchungen ueber      die    
,befruchtungsvorgang bei den            
,phanerogamen1 ,jena1 #ahhd4 ,an        
interesting summary of recent work on   
,xenia and double      fertilisation    
will be found in ,bull4 ,no4 #bb1 ,u4,s4
 ,dept4 of      ,agric41 #aijj4 ,see    
also ,nature1 ,mar4 #ae1 #aijj1 p4 #dgj4
       ,if he wishes to explore the vast
 region of controversial      literature
 that opens up from these points1 and   
which is far      beyond the purpose of 
this book1 he may consult the literature
      collected in ,kassowitz'          
,allgemeine ,biologie1 ,wien1 #ahii1 ,b4
      ,,ii41 and the references in the  
works quoted2 also1      ,strasburger1  

,the ,periodic ,reduction of            
,chromosomes in ,living      ,organisms1
 ,ann4 ,bot41 viii41 #ahid1 p4 #bha4    
,for ,mendel's      ,law1 see ,correns  
in ,ber4 d4 deutsch4 bot4 ,gesellsch41  
vol4      xviii41 #aijj1 p4 #aeh4       
,,part ,,ii4  ,,disease ,,in ,,plants4  
,,chapter ,,ix4  ,,phytopathology4      
,,derivation ,,and ,,meaning4           
,history4 ,references in the            
,bible--,greeks and ,romans--           
,shakespeare--,rouen                    
law--,superstitions--,malpighi and      
,grew--                                 
,hales--,unger--,berkeley--,de ,bary1   
etc4 ,physiology and ,biology           
--,diagnosis--,etiology--,therapeutics4 
,study of causes4   ,phytopathology1    
from ,greek words which signify to treat
 of diseases of plants1 comprises what  
is known of the symptoms1 course1 and   
causes of the diseases which threaten   
the lives of plants1 or bring about     
injuries and abnormalities of structure4
 ,as a distinct and systematised branch 

of botany it is a modern study1 the     
history of which only dates from about  
#ahej1 though the subject had been      
treated more or less disjointedly by    
several authors during the preceding    
century1 and isolated records of        
diseased crops1 fruit-trees1 etc41 exist
 far back in the history of ,europe4    
,the existence of mildews and blights on
 cereals indeed was observed and        
recorded by the writers of the older    
books of the ,bible1 half a dozen       
references to such blights being found  
in the ,old ,testament1 as well as      
others to blasted fig trees1 etc41 in   
the ,new ,testament4 ,aristotle1 about  
#cej ,b4,c41 noticed the epidemic nature
 of wheat-rust4 ,the ,greeks and ,romans
 were so well acquainted with such      
diseases that their philosophers        
speculated very shrewdly as to causes1  
while the people dedicated such pests to
 special gods4 ,as regards the ,middle  
,ages1 we know little beyond the fact   
that blights and mildews existed1 but   

,shakespeare's reference in ,king ,lear 
7,act ,,iii41 ,sc4 #d7 leaves no doubt  
as to his acquaintance with mildew in   
the #agth century1 and other authorities
 bear out the same4 ,even the law took  
cognisance of the danger of wheat-rust  
in #affj in ,rouen 7,loverdo74 ,prior to
 the #ahth century1 however1 only meagre
 notes on the subject occur scattered   
here and there among other matters1 and 
much superstition existed then and later
 regarding these as other diseases4     
,malpighi1 in #afgi1 gave excellent     
figures of leaves rolled by insects and 
of numerous galls1 the true nature of   
which he practically discovered by      
observing the insect piercing the       
tissues2 previous observers--,pliny knew
 that flies emerge from galls1 but      
thought the latter grew                 
spontaneously--having nothing but       
superstitions and conjectures to offer4 
,grew1 in #afhb1 also gave a capital    
figure and description of a leaf mined  
by a small flat insect 4 4 4 which      

neither ranging in breadth nor striking 
deep into the leaf1 eats so much only as
 lies just before it1 and so runs       
scudding along betwixt the skin and the 
pulp of the leaf1 leaving a whitish     
streak behind it1 where the skin is now 
loose1 as the measure of its voyage--a  
by no means inadequate description of   
the injury and its cause4  ,during the  
eighteenth century several academic     
treatises or dissertations dealing with 
diseases of plants appeared4  ,but as a 
rule we only find disjointed notes4     
,hales 7#agbg-cc7 discusses the rotting 
of wounds1 canker1 and a few other      
matters1 but much had to be done with   
the microscope ere any substantial      
progress could be made4  ,with the      
nineteenth century1 and the founding of 
the modern theories of nutrition by     
,ingenhousz1 ,priestley1 and ,de        
,saussure1 we find a new era started4   
,as the discoveries of the microscopists
 continued to build up our knowledge of 
the anatomy of plants and began to      

elucidate the biology of the fungi and  
other cryptogams1 while the chemists and
 physiologists laid the foundations of  
our modern science of plant life1 it    
gradually became possible to tabulate   
and classify plant diseases1 and discuss
 their symptoms and causes in a more    
scientific manner4 ,even in #ahcc1      
however1 ,turpin1 and a far better      
observer1 ,unger1 regarded parasitic    
fungi as due to diseased outgrowths of  
chlorophyll-corpuscles and parenchyma   
cells1 views shared by ,meyen 7#ahcg7   
and ,schleiden 7#ahdf74 ,we may pass    
over the various treatises of ,wiegmann 
7#ahci71 ,meyen 7#ahda71 ,raspail       
7#ahdf71 ,kuehn 7#ahei71 and a number of
 other works of the period1 merely      
referring with emphasis to ,berkeley's  
admirable papers in the ,gardener's     
,chronicle 7#ahed7 for a summary of what
 was then known4 ,all these works       
antedate ,de ,bary's ,morphologie und   
,physiologie der ,pilze1 etc4 7#ahff71  
in which he brought together the results

 of his researches during the decade1   
proving the real nature of parasitic    
diseases and infection as worked out by 
experiments between #ahec and #ahfc4    
,this work put the whole subject of     
parasitic diseases of plants and animals
 on a new footing1 and paved the way for
 the modern treatment of plant pathology
 as elaborated in the treatises of      
,frank 7#ahhj and #ahie71 ,sorauer      
7#ahhf71 ,kirchner 7#ahij71 and others1 
to which the reader is referred for     
further details4 ,i will merely quote   
the following passage from ,raspail's   
,histoire ,naturelle de la ,sante et de 
la ,maladie1 #ahdf 7vol4 ii41 p4 #agf71 
in illustration of the views entertained
 by high authorities just prior to ,de  
,bary's work3 ,l'insecte qui produit les
 erineum1 uredo1 aecidium1 xyloma1      
puccinia1 n'est donc plus pour nous un  
insecte inconnu1 mais un acarus 7grise71
 un aphis 7puceron7 ou un thrips1 qui   
produit au printemps une deviation1 etc4
  ,and this view1 that fungi already    

well known to mycologists were called   
forth by the punctures of insects1 was  
regarded as not out of harmony with the 
idea that the fungus itself was an      
abnormal outgrowth of the tissues of the
 host4  ,the proper study of plant      
pathology presupposes and involves a    
knowledge of the physiology of plants1  
of the normal relations of the latter to
 their environment1 and of the biology  
of those animals and plants 7principally
 insects and fungi7 which are parasitic 
on them4 ,it is of the first importance 
to understand that a disease is a       
condition of abnormal physiology1 and   
that the boundary lines between health  
and ill-health are vague and difficult  
to define4 ,as with the study of the    
diseases of man and other animals1 so   
with those of plants1 the practice      
resolves itself into the accurate       
observation and interpretation of       
symptoms 7,diagnosis7 on the one hand1  
and of causes 7,aetiology7 on the other1
 before any conclusions of value can be 

drawn as to preventive or remedial      
measures 7,therapeutics74 ,in plants1   
however1 symptoms of disease are apt to 
exhibit themselves in a very general    
manner1 or at any rate it may be that   
our perceptions of them differentiate   
symptoms due to very different reactions
 imperfectly1 probably because the      
organisation of the plant is less       
specialised than that of animals4 ,the  
turning yellow and premature falling of 
leaves1 for instance1 is a frequent     
symptom of disease2 but it may be due to
 a long series of different causes of   
ill-health--e4g4 drought1 too high or   
too low a temperature1 light of         
insufficient or of excessive intensity1 
a superfluity of water at the roots1 the
 presence in the tissues of parasitic   
fungi1 or that of worms or insects at   
the roots or elsewhere1 poisonous gases 
in the air1 soil1 etc41 and so forth4   
,consequently the science of plant      
pathology is much concerned with the    
direct action of external causes1 which 

are probably less obscure than in the   
case of animals1 though by no means     
always obvious4 ,such considerations at 
any rate seem to account for the fact   
that most authorities on plant pathology
 base their classification on the causes
 of disease1 there being few noteworthy 
exceptions4   ,,notes ,,to ,,chapter    
,,ix4       ,the bibliography here      
quoted will be found in ,berkeley1      
,vegetable ,pathology1 ,gardener's      
,chronicle1 #ahed1 p4 #d2               
,plowright1 ,british ,uredineae and     
,ustilagineae1 #ahhi2 ,eriksson      and
 ,henning1 ,die ,getreideroste1         
,stockholm1 #ahif2 ,de ,bary1           
,comparative ,morphology and ,biology of
 the ,fungi1 etc41 #ahhg2      ,frank1  
,die ,krankheiten der ,pflanzen1        
#ahie-if1 and scattered      in the     
works referred to in them and in the    
text4     ,,chapter ,x4  ,,health ,,and 
,,disease4                              
,variation--,disease--,comparison to a  
top4 ,health--,extinction      of       

species--,natural demise4 ,examples of  
complex interactions      in            
health--,interference1 and tendencies to
 ill-health4   ,when we come to enquire 
into the causes of disease1 it appears  
at first an obvious and easy plan to    
subdivide them into groups of factors   
which interfere with the normal         
physiology of the plant4 ,scientific    
experience shows1 however1 that the easy
 and the obvious are here1 as elsewhere 
in nature1 only apparent1 for disease1  
like health1 is an extremely complex    
phenomenon1 involving many reactions and
 interactions between the plant and its 
environment4 ,if we agree that a living 
plant in a state of health is not a     
fixed and unaltering thing1 but is ever 
varying and undergoing adaptive changes 
as its life works out its labyrinthine  
course through the vicissitudes of the  
also ever-varying environment1 then we  
cannot escape the conviction that a     
diseased plant1 so long as it lives1 is 
also varying in response to the         

environment4 ,the principal difference  
between the two cases is1 that whereas  
the normal healthy plant varies more or 
less regularly and rhythmically about a 
mean1 the diseased one is tending to    
vary too suddenly or too far in some    
particular directions from the mean2 the
 healthy plant may1 for our present     
purposes1 be roughly likened to a       
properly balanced top spinning regularly
 and well1 whereas the diseased one is  
lurching here1 or wobbling there1 to the
 great danger of its stability4 ,for we 
must recognise at the outset that       
disease is but variation in directions  
dangerous to the life of the plant4     
,health consists in variation also1 but 
not in such dangerous grooves4 ,that the
 passage from health to disease is      
gradual and ill-defined in many cases   
will readily be seen4 ,in fact we cannot
 completely define disease4 ,mere       
abnormality of form1 colour1 size1 etc41
 is not necessarily a sign of disease1  
in the usual sense of the word1         

otherwise the striking variations of our
 cultivated plants would suggest gloomy 
thoughts indeed1 whereas we have reason 
to believe that many cultivated         
varieties are more healthy--in the sense
 of resisting dangerous exigencies of   
the environment--than the stocks they   
came from4 ,strictly speaking1 no two   
buds on a fruit-tree are alike1 and the 
shoots they produce vary in position1   
exposure1 number1 and vigour of leaves1 
and so forth4 ,the minute variations    
here referred to are not seen by the    
ordinary observer1 but those who bud1   
graft and multiply by cuttings on a     
large scale know that such              
bud-variations are important1 quite     
apart from more extensive sports which  
occasionally occur4  ,on the other hand1
 we have reason to believe that many    
species have died out gradually as the  
environment altered4 ,these plants died 
because they did not vary sufficiently1 
or did not vary in the right directions2
 they became diseased with respect to   

the then prevailing conditions of normal
 physiology or health4  ,disease1       
therefore1 may be said to be variation  
of functions in directions1 or to       
extents1 which threaten the life of the 
plant1 the normal in all cases being the
 state of the plant characteristic of   
the species4  ,even now1 however1 we    
have not obtained a complete definition1
 because1 since all plants die sooner or
 later1 we have not excluded the natural
 demise of the individual or its parts1 
and no one would call the autumnal fall 
of leaves1 or the withering of an annual
 after flowering1 death from disease4   
,clearly then the idea of disease       
implies danger of premature death1 and  
probably this is as near as we shall get
 to a satisfactory definition4 ,since   
this matter is of primary importance for
 our present theme1 ,i will add the     
following instances for consideration4  
,a plant in perfect health and in the   
fullest exercise of all its functions1  
has its roots in a soil which is        

suitably warmed and aerated1 contains   
the right quantities of water which     
dissolve just the proper proportions of 
all the essential mineral salts1 but    
nothing poisonous1 while the soil itself
 has a texture such that the roots and  
root-hairs can extend and do their      
utmost in absorbing4  ,the leaves above 
are exposed to just the right intensity 
of light1 in air which is not too dry1  
and is of suitable temperature and      
composition1 containing no poisonous    
exhalations1 etc42 and as the foliage is
 gently moved by the breeze1 it         
manufactures carbohydrates at the       
optimum rate in the chlorophyll1 and the
 so-called elaborated sap containing the
 dissolved organic food-supplies is     
prepared in the tissues in maximum      
quantities and of just the right degrees
 of concentration and quality for use in
 the buds1 stem1 roots1 etc41 for which 
it is destined as they draw on the      
supplies4  ,between these assimilating  
organs1 the leaves1 and the absorbing   

roots1 we have in the stem the wood1    
with its vessels adapted in quantity and
 calibre to convey the water containing 
dissolved salts from the absorbing roots
 to the leaves 7to say nothing of other 
parts7 and1 separated from this wood by 
the cambium1 we find the sieve-tubes and
 cortical tissues in suitable quantity  
conveying the elaborated sap--the       
solutions of organic food-materials from
 the leaves down to the roots1 up to the
 buds1 and elsewhere4 ,joining these    
cortical and wood tissues are adapted   
series of medullary rays which1 apart   
from other connections1 bring about the 
necessary interchanges of water and     
elaborated sap with the cambium1 the    
formative tissue which has to be fed and
 served by them1 and which by its growth
 supplies new vessels and sieve-tubes1  
etc41 to carry the continually          
increasing quantities of water and food 
substances as the roots and leaves      
increase in number and area1 and thus   
enables this ideally correlated system  

to go on working at maximum energy4     
,now suppose the same plant with its    
roots in an unsuitable soil--too dry or 
too poor in mineral supplies1 for       
instance--the transpiring leaves above  
cannot obtain sufficient water and salts
 to supply their needs1 but we will     
suppose hypothetically that they still  
assimilate under the same ideal         
conditions as before4 ,the supplies now 
coming to the cambium are diminished1   
since the want of water and minerals    
compels the leaves to put aside any     
excess of carbohydrates 7e4g4 as stored 
starch-grains71 and the plastic         
materials which do pass to the cambium  
so deficient in water cannot be directly
 utilised1 and a starvation period sets 
in4 ,consequently the cambium forms less
 wood1 and this will contain fewer and  
smaller vessels1 and so reduce the      
conducting passages3 fewer sieve-tubes  
also are constructed1 and the paths of  
the water current and food supplies     
narrowed1 which of course reacts on the 

tissues everywhere4 ,the reserve        
substances may slowly be dissolved and  
distributed1 however1 and considerable  
quantities be passed in course of time  
into the roots1 which1 as opportunity   
offers1 gradually employ them in making 
new roots1 and if the disturbance has   
not gone too far and the conditions do  
not become unfavourable1 an increased   
root-supply may by its larger absorbing 
area gradually establish the former     
state of equilibrium of functions4 ,but 
this at the expense of the plant1 which 
is smaller1 has fewer leaves and        
narrower water channels1 etc41 than a   
plant not thus checked1 and it may take 
a long time to make up for the loss of  
time and stature thus incurred4 ,indeed 
if the plant is an annual no recovery at
 all may occur1 the reserves passing    
into fruit and seeds instead of slowly  
supplying the roots as described4  ,if  
it be asked1 can such a condition of    
affairs as that described really occur1 
we have only to think of a transplanted 

specimen with its roots maimed and put  
into unsuitable soil1 or of plants in   
the open with feeding roots gnawed by an
 insect1 etc41 or of a tree hitherto in 
equilibrium with its fellows in a       
plantation suddenly set free by thinning
 and so forth4  ,now take the case where
 the roots are maintaining their maximum
 functional activity1 but the           
leaves--owing to want of light1 too much
 moisture or too low a temperature of   
the air--are functionally depressed4    
,here we get a state of over-saturation 
with water set up1 the tissues are      
turgid to bursting point1 what supplies 
do traverse the sieve-tubes1 cortex1    
etc41 do so slowly and are excessively  
diluted1 and the cambium again forms    
less wood1 but the lumina of the vessels
 are larger and the lignification less  
complete4 ,growth in length is          
excessive1 but more leaves are formed1  
though they are apt to be abnormally    
thin and may be small4 ,little or no    
reserves are stored anywhere1 and the   

watery tissues contain dangerously      
diffusible substances which may render  
them an easy prey to parasitic fungi4   
,here again1 however1 if the disturbance
 of equilibrium has not gone too far1   
and if the season permits1 the new      
leaves may come into full activity and  
the situation be saved by transpiration 
and assimilation gradually increasing   
and restoring the equilibrium4 ,but1 as 
before1 the plant has suffered1 and     
shows the effect in its weak shoots1    
retarded flowering1 and other ways4     
,such plight as is here described may   
actually be attained in greenhouses     
where over-watering is the fault1 and   
even in the open it is not uncommon in  
rainy summers1 or in plantations where  
dominant trees get the upper hand and   
partially shade more slowly growing     
species1 or in fields where rank grass  
is allowed to overwhelm crops of lower  
stature4  ,now it will be evident that  
either of these typical cases of        
temporary disturbance of functional     

equilibrium may be carried too far3 in  
the first case the plant may wilt and   
wither1 in the second it may rupture and
 rot1 to take these eventualities only4 
,and yet it is difficult to call these  
indispositions diseases3 they are rather
 examples of extreme departures from the
 normal standard of health1 just on the 
borderland between health and disease4  
,a step further1 as it were1 and disease
 supervenes3 certain tissues die from   
want of water1 and a necrotic area is   
formed1 or the cortex bursts and a wound
 is formed in another way1 or some      
fungus gets a hold1 and so on4 ,these   
abnormal states are particularly apt to 
predispose the plant to disease--insects
 revel in such semi-wilted leaves and   
shoots crammed with reserves1 and fungi 
in the water-logged leaves of the second
 case1 while a cold dry wind is         
peculiarly fatal to such tissues4       
,,notes ,,to ,,chapter ,x4       ,the   
reader may consult ,hartig1 ,diseases of
 ,trees1 ,eng4 ed41      #ahid1         

,introduction2 ,sorauer1 ,pflanzen      
,krankheiten1 pp4 #a-ab1      and       
,frank1 ,die ,krankheiten der ,pflanzen1
 ,b4 #a1 p4 #e1 for      definitions of 
disease4     ,,chapter ,,xi4  ,,causes  
,,of ,,disease4       ,a4 ,external     
causes--,i4 ,non-living environment3    
soil1      atmosphere1                  
temperature--,,ii4 ,living environment3 
plants1      animals--,complex          
interactions--,predisposing causes--,no 
one      factor works alone--,tangled   
problems of natural selection           
involved4 ,b4 ,so-called internal       
causes4   ,it is customary to classify  
the causes of disease in plants into two
 principal groups--7#a7 those due to the
 action of the non-living               
environment--soil1 atmosphere1 physical 
conditions such as temperature1 light1  
etc42 and 7#b7 those brought about by   
the activities of living                
organisms--plants and animals of various
 species4 ,before passing to further    
subdivisions under these two heads1     

however1 it is necessary to observe that
 no disease can be efficiently caused by
 an organism alone1 since its powers for
 injury as a parasite1 or otherwise1 are
 affected by its non-living environment 
as well as by the host-plant4 ,for      
instance1 the spores of a parasitic     
fungus which would infect and rapidly   
destroy a potato plant in moist warm    
weather may be showered on to such a    
plant with impunity if the air remains  
dry and cool--or on to a cabbage under  
any circumstances as far as we know4    
,again1 probably no one factor of the   
non-living environment ever suffices to 
induce a disease1 possibly because no   
such thing as only one change at a time 
ever occurs4 ,for instance1 it is       
difficult to say1 when a soil becomes   
sodden with water1 whether the excess of
 water and dissolved matters1 the want  
of air displaced by the water1 the      
lowering of the temperature1 or the     
accumulation of foul products1 etc41 is 
the principal factor in causing the     

damage which results1 and we have to    
determine by the balance of experimental
 evidence which is the dominant factor  
in all such cases4  ,the study of       
aetiology of disease is in fact only a  
particular case of that of aetiology in 
general4 ,plants at high altitudes in   
the ,alps acquire very different        
characteristics from the same species in
 the plains4 ,is this due to the low    
temperature1 the rarer atmosphere1 the  
more intense illumination1 the changes  
in moisture1 etc41 etc48 ,the question  
is more difficult than it appears at    
first sight1 and we must remember that1 
complex as are the factors working on   
the host1 they are equally complex in   
their actions on a parasite attacking   
the host1 whence the resulting disease  
becomes indeed a tangled problem of     
natural selection4  ,finally it remains 
to say a few words about a numerous     
class of cases where no external cause  
of disease can be discovered4 ,it was   
formerly the custom to group such cases 

of ,internal ,causes by themselves1 but 
apart from the fact that many of these  
mysterious diseases have subsequently   
been shown to be due to the action of   
external agencies1 the whole question of
 internal causes resolves itself into   
one of relations between the plant and  
its surroundings1 and it becomes evident
 that no inherited or internal disease  
can be regarded as explained until we   
know the external causes which have so  
modified the structure and working of   
the living cells as to make them        
abnormal in their reactions to other    
parts of the plant4 ,internal causes of 
disease1 therefore1 is a phrase         
expressing our ignorance1 but somewhat  
more emphatically than usual4 ,if this  
is clearly understood there seems no    
reason against its employment for the   
time being in the artificial scheme of  
classification we require4 ,with regard 
to external causes due to the non-living
 environment1 excess or deficiency of   
materials in the soil1 water1 or        

atmosphere plays an important part1     
and--since we may neglect purely aquatic
 plants--it is customary to speak of    
diseases due to unsuitable soils or to  
injurious atmospheric influences4 ,for  
instance1 any deficiency in the supplies
 of the necessary mineral salts         
7compounds of calcium1 magnesium1       
potassium with sulphuric1 nitric and    
phosphoric acids1 etc47 leads to        
pathological changes1 as also does the  
lack of the necessary traces of iron4   
,but it is equally true that the        
presence of such ingredients in excess  
or in combinations unsuited to the      
plants also leads to disaster1 as also  
does the presence of minerals or other  
compounds which poison the              
root-hairs--e4g4 products of            
decomposition1 soluble salts of copper  
and other poisons4 ,that these matters  
are bound up with the whole question of 
manuring and of proper soil-analyses    
will be evident4  ,another essential    
factor is the nature and quantity of    

organic materials in the soil1 whether  
leaf-mould and decomposing vegetable    
remains1 stable manures1 or other animal
 matters1 all of which affect different 
species very differently1 and produce   
very different results in different     
soils4 ,it is necessary to apprehend in 
this connection what has been stated    
above3 that soil is not a mere dead     
structureless medium1 and that the      
root-hairs of ordinary plants cannot    
deal with large quantities of putrefying
 organic matter3 that a good soil must  
abound in useful bacteria and fungi to  
render such substances available--and in
 very various ways--and that it must be 
open and aerated1 of proper temperature 
and suitably supplied with water1 and so
 forth1 or disaster will result4 ,here1 
again1 then we are brought into close   
contact with all that is known of       
fermentation1 nitrification1 and the    
various biological changes going on in  
soil1 and the application of such       
knowledge to the practice of manuring   

and tillage in all its forms4  ,in view 
of the above remarks1 the danger of     
over-feeding1 in this sense1 has a real 
meaning for horticulturists1 though it  
must not be forgotten that no substance 
is really a food until it is assimilable
 into the protoplasm3 manures1 etc41 are
 food-materials1 not food4 ,the futility
 of mere chemical analyses to prove what
 a plant requires is now well known1 and
 it is only on the basis of long and    
carefully conducted experiments that we 
can ever discover what a particular     
plant in a particular soil1 situation1  
and climate requires for healthy        
development4 ,again1 the quantity of    
water in soil may be too great or too   
small for given species1 and this either
 on the average for the year1 or during 
critical periods only2 and it is        
obviously important whether the excess  
or deficiency is due to improper        
supplies of water1 the depth or         
shallowness of the soil1 its retentive  
powers1 or the nature of the sub-soil   

and so on1 again bringing the whole     
matter into connection with our         
understanding of the physical           
constitution and structure of soils1 and
 the nature of soil-drainage4  ,for     
instance1 a common way of killing ferns 
is to keep the roots and soil wet and   
the air and fronds dry1 whereas the     
natural habitats provide for wet and    
shaded fronds and well-drained soil4    
,it may be noted here that in most cases
 where gardeners speak of plants being  
killed under the drip of trees--e4g4    
,beech1 the injury is due1 not to the   
effects of water but to the shade3 the  
loss of light is so great that the      
shaded plants die of inanition because  
their leaves are not able to provide    
sufficient carbohydrates4  ,closely     
bound up with this is the question of   
the gases in soils4 ,apart from the     
disastrous effects of poisons--e4g4 coal
 gas escaping from pipes under pavements
 in towns1 etc41 diseased conditions    
often result from deficiency of oxygen  

at the root-hairs1 due to imperfect     
aeration of soils1 brought about by     
stagnant water1 excess of animal matter1
 and so forth4  ,unsuitable constitution
 of the atmosphere is also a fruitful   
source of disease1 though its effects   
are commoner in closed stoves and       
greenhouses than in the open4           
,nevertheless the continual exhalation  
of sulphurous fumes1 chlorine1 and other
 poisonous gases in the neighbourhood of
 manufacturing centres or of large smoky
 towns1 volcanoes1 etc41 play their part
 in injuring plants2 and excessive      
moisture in the form of mist1 rain1     
etc41 is also important4 ,all these     
matters bring us at once into the region
 of physiology1 and only an intelligent 
appreciation of what is known about the 
action of the atmosphere on the soil and
 the plant will save the peasantry of a 
country from a hopeless mysticism but   
little removed from that of the ,middle 
,ages1 when blights and other evils were
 vaguely referred to the river-mists1   

thunder clouds1 and easterly winds4  ,if
 we summarise the above as the material 
factors of the environment1 we may      
classify another set of external        
non-living causes of disease as the     
non-material factors4 ,such are         
principally the following3  ,the space  
at the disposal of plants greatly       
affects their welfare4 ,the crowding of 
roots in the soil and of foliage in the 
air1 resulting in the loss of light to  
the leaves1 involves deficiency of all  
the materials referred to               
above--minerals1 organic materials1     
gases1 and water--and no better         
illustration of the intense struggle for
 existence among these apparently       
passive and motionless beings1 plants1  
can be given than an over-crowded       
seedbed or plantation4 ,if left to      
themselves such over-stocked areas      
exhibit to the keen eye of the trained  
observer all the phases of starvation1  
weakness1 wounding1 rot1 and1 so to     
speak1 brutal dominance of the stronger 

over the weaker which it is the object  
of cultivation to prevent4 ,here1 then1 
we are brought face to face with the    
true significance of thinning and       
weeding out1 pruning1 and similar       
processes4  ,unsuitable temperature is  
one of the commonest of all sources of  
disease1 for every plant is adapted to  
certain ranges of temperature1 and best 
adapted to a given optimum somewhere    
between the maximum and minimum         
temperature for each function4          
,consequently any serious departure from
 the mean may bring about physiological 
disturbances of the nature of disease1  
and this in very various ways1 as       
exemplified by the results of frost1    
sun-scorching1 drought1 hail-storms1    
forest fires1 and so forth4  ,as a      
predisposing factor to disease abnormal 
temperature effects play a great part4  
,many wound-fungi gain their entrance   
through frost-cracks1 bruises due to    
hailstones1 or into tissues chilled     
below the normal4  ,no less remarkable  

are the diseases primarily due to       
insufficient or improper exposure to    
light1 which affects the                
chlorophyll-apparatus and the process of
 carbon-assimilation and through these  
the whole well-being of the plant4      
,every plant is adapted to certain      
ranges of light intensity1 and most     
cultivators know how impossible it is to
 grow shade plants in fully exposed     
situations1 and how easily plants which 
live in open sunny situations are drawn 
and killed by shade4 ,it is equally     
important to have the right kind of     
light1 as disastrous experiences with   
greenhouses glazed with glass which cut 
off certain rays of light have taught4  
,here1 again1 it is important to notice 
that the optimum intensity or quality of
 light may differ for different         
functions and organs of the plant1 as is
 shown by many adaptations on the part  
of species growing in natural           
situations--e4g4 bud protection1        
orientation of leaves1 etc4--and it may 

be taken as a rule that etiolated plants
 are peculiarly susceptible to other    
diseases4  ,as regards other factors of 
the inorganic environment1 disasters    
which come within the scope of our      
subject may be brought about by many    
agencies1 the mechanical effects of snow
 and hail1 wind1 avalanches1 etc41 the  
effects of lightning1 and so forth1     
being a few of them4   ,,notes ,,to     
,,chapter ,,xi4       ,for other        
detailed classifications of the causes  
of disease      the reader is referred  
to the works of ,sorauer and of ,frank  
referred to in the last chapter4 ,also  
,kirchner1 ,pflanzen      ,krankheiten1 
,stuttgart1 #ahij4       ,of more       
historical importance are the older     
classifications of      ,berkeley1      
,gardeners' ,chronicle1 #ahed1 and ,re1 
,gardeners'      ,chronicle1 #ahdi-ej4  
,these latter are interesting as showing
      the very different views held by  
the earlier workers1 and      comparison
 of these with the modern views helps to

 mark the      progress of physiology   
during the half century which has       
intervened4     ,,chapter ,,xii4        
,,causes ,,of ,,disease4 ,,the ,,living 
,,environment4       ,causes due to     
animals--,vertebrata--,wounds1          
etc4--,invertebrata      --,insects1    
etc4--,plants as causes of              
disease--,phanerogams1      weeds1      
etc4--,cryptogams1 fungi--,epidemics1   
etc4   ,passing now to those causes of  
disease which are connected with the    
living environment1 we may obviously    
divide them into two groups of agents1  
animals and plants4  ,among animals1 the
 various vertebrata1 including man1 are 
especially responsible for the larger   
kinds of wounds and wholesale           
destructive processes due to breakage1  
stripping of leaves and bark1 cutting   
and biting1 and so forth4 ,cattle1      
rabbits1 rats and mice1 squirrels and   
birds of various kinds stand out        
prominently as enemies to trees and     
other plants1 to which they do immense  

injury in various ways by their horns1  
teeth1 claws1 and beaks2 and the damage 
which an ignorant gardener or forester  
can do with his ill-guided footsteps1   
axe1 spade1 and knife can only be       
appreciated by one who knows the habits 
of plants4  ,it is among the            
invertebrata1 however1 especially       
insects and worms1 that the most        
striking agents of disease in plants are
 to be found1 for1 with the exception of
 certain rodents--and we may logically  
include also human invasions--vertebrate
 animals do not often appear in such    
numbers as to bring about the epidemics 
and scourges only too commonly caused by
 insect pests4  ,insects injure plants  
in very various ways4 ,some1 such as    
locusts1 simply devour all before them2 
others1 e4g4 caterpillars1 destroy the  
leaves and bring about all the phenomena
 of defoliation4 ,others1 again1 eat the
 buds--e4g4 ,grapholitha2 or the        
roots--e4g4 wire-worms1 and so maim the 
plant that its foliage and assimilation 

suffer1 or its roots become too scanty  
to supply the transpiration current4    
,many aphides1 etc41 puncture the       
leaves1 suck out the sap1 and produce   
deformations and arrest of leaf-surface1
 as well as actual loss of substance1   
and when numerous such insects induce   
all the evils of defoliation4 ,others1  
such as the leaf-miners1 tunnel into the
 leaves1 with similar results on a      
smaller scale4  ,it must be remembered  
that a single complete defoliation of a 
herbaceous annual1 or even of a tuberous
 plant like the potato1 so incapacitates
 the assimilatory machinery of the      
plant1 that no stores can be put aside  
for the seeds1 tubers1 etc41 of another 
year1 or at most so little that only    
feeble plants come up4  ,in the case of 
a tree the case is different1 and since 
most large trees in full foliage have   
far more assimilatory surface than is   
actually necessary for immediate needs1 
a considerable tax can be paid to       
parasites or predatory insects before   

the stores suffer perceptibly4 ,still1  
it should be recognised that the injury 
tells in time1 especially in seed years4
  ,many larvae of beetles1 moths1 etc41 
bore into the bark and as far as the    
cambium or even into the wood or pith of
 trees1 the local damage inducing       
general injuries in proportion to the   
number of insects at work3 moreover1 the
 wounds afford points of entrance for   
fungi and other pests4  ,galls and      
similar excrescences result from the    
hypertrophy of young living tissues     
pierced by the ovipositors of various   
insects1 and irritated by the injected  
fluid and the presence of the eggs and  
larvae left behind4 ,they may occur on  
the buds1 leaves1 stems1 or roots1 as   
shown by various species of ,cynips on  
oak1 ,phylloxera on vines1 etc41 in all 
cases the local damage being relatively 
small1 but the general injury to        
assimilatory1 absorptive1 and other     
functions is great in proportion to the 
number of points attacked4  ,many       

grubs--larvae of flies1 beetles1        
etc4--bore into the sheaths or          
internodes of grasses1 or the pith of   
twigs1 or into buds1 fruits1 and other  
organs of plants1 and do harm           
corresponding to the kind and amount of 
tissues injured4  ,various species of   
so-called eelworms--,nematodes--also    
cause gall-like swellings on young      
roots1 or they invade the grains of     
cereals4  ,finally1 various slugs and   
snails cause much injury by devouring   
young leaves and buds and diminishing   
the assimilatory area4  ,plants as      
agents of disease or injury fall        
naturally into the two main categories  
of flowering plants 7,phanerogams7 and  
,cryptogams1 among which the fungi are  
the especially important pests4         
,beginning with weeds1 we find a large  
class of injurious agents4 ,weeds damage
 the plants we value by crowding them   
out in the struggle for existence1 as   
already stated1 and when the weed-action
 is simply due to superfluous plants of 

the same species1 we speak of           
overcrowding4 ,but it must not be       
overlooked that the competition between 
crowded plants of the same              
species--where every individual is      
acting as a weed to the others--may be  
more dangerous than between plants and  
weeds belonging to other species and    
genera1 because in the former case they 
are struggling for the same minerals and
 other necessary food-materials3 a      
matter of importance in connection with 
the rotation of crops4  ,the question of
 allowing grass to grow at the foot of  
fruit trees1 as in orchards1 is a good  
case in point4 ,such grass may increase 
the damp and shade1 thus favouring fungi
 at one season1 and dry up the moisture 
of the soil to the injury of the fine   
superficial roots at another1 as well as
 exhaust the soil1 owing to the         
competition of the roots for salts and  
other materials4 ,on the other hand1 the
 checking of surface roots by           
competition with the grass has been     

claimed as advantageous4 ,in this       
connection probably the whole question  
of the composition of the turf arises1  
as well as that of possible cropping for
 hay1 and manuring4  ,as regards any    
particular weed1 the cultivator should  
learn all he can respecting its         
duration1 seeding capacity1 method of   
dissemination1 the depth and spread of  
its root-system1 and any other          
particulars which enable him to judge   
when and how to attack it4 ,it is only  
necessary to see the victory of such    
drought-resisting weeds as ,hieracium   
pilosella1 ,plantains1 ,hypochaeris1 on 
lawns to realise how weeds may win in   
the struggle for existence with the     
finer grasses4  ,many so-called weeds   
are1 however1 partially parasitic1 with 
their roots on the roots of others--e4g4
 ,rhinanthus1 ,thesium1 etc41 and much  
damage is done to meadow grasses and    
herbage by the exhaustive tax which     
these semi-parasites impose4  ,this is  
carried still further in the case of    

such root-parasites as ,orobanche1 where
 the host-plant is burdened with the    
whole support of the pest1 because the  
latter1 having no chlorophyll1 is       
entirely dependent on the former for all
 its food4  ,even ordinary climbing     
plants may injure others by shading     
them1 either by scrambling over their   
branches--e4g4 ,bramble1 or twisting    
their tendrils round the twigs--e4g4    
,bryony1 or twining round them--e4g4    
,woodbine1 ,convolvulus1 etc4 ,the      
principal direct injury is in these     
cases owing to the loss of light        
suffered by the shaded foliage1 but the 
weed-action is often increased by the   
competition of their roots--e4g4 briars2
 and in the case of woody climbers the  
gradually increased pressure of the     
woody-coils round the thickening stems  
compresses the cambium and cortex of the
 support and induces strictures and     
abnormalities which may be fatal in     
course of time4  ,epiphytes1 or plants  
which support themselves wholly on the  

trunks1 branches1 or leaves of other    
plants1 also injure the latter more     
especially by shading their             
foliage--e4g4 tropical ,figs1 ,orchids1 
,aroids1 etc42 and similar damage is    
done by our own ,ivy1 the main roots of 
which are in the soil1 but the numerous 
adventitious roots of which cling to the
 bark4  ,when the climber or epiphyte is
 also parasitic1 as in the case of the  
,dodder1 ,loranthus1 ,mistletoe1 etc41  
the direct loss of substance stolen from
 the host by the parasite comes in to   
supplement any effect of shading that   
the latter may bring about if it is a   
leafy plant4  ,of ,cryptogams1 apart    
from a few epiphytic ferns1 and the     
intense weed-action of certain          
,equisetums1 the rhizomes and roots of  
which are as troublesome as those of    
twitch and other phanerogamic weeds1 it 
is especially the fungi which act as    
agents of disease1 and which1 as we now 
know1 are par excellence the causes of  
epidemics4  ,the action of fungi may be 

local or general2 and restricted1 slow  
and insidious1 or virulent and rapidly  
destructive4  ,examples of local action 
are furnished by ,schinzia1 which forms 
gall-like swellings on the roots of     
rushes2 ,gymnosporangium1 which induces 
excrescences on the stems of junipers1  
and numerous leaf-fungi 7,puccinia1     
,a,ecidium1 ,septoria1 etc471 which     
cause yellow1 brown1 or black spots on  
leaves1 as well as by ,ustilago1 which  
attacks the anthers or the ovary of     
various plants1 and so forth4 ,in such  
cases the injury done by a few centres  
of infection is very slight1 but        
prolonged action may bring into play    
secondary effects such as the gradual   
destruction of the cambium round a      
branch1 when1 of course1 the effect of  
ringing results2 or if the fungus       
becomes epidemic and myriads of         
leaf-spots are formed1 the destruction  
of foliar tissue1 gradual taxing of the 
assimilatory cells1 etc41 may end in    
rapid defoliation1 and renewed attacks  

soon exhaust the plants and lead to     
sterility and death1 as often occurs    
with ,uredineae--e4g4 the coffee        
leaf-disease4  ,it is highly probable   
that such fungi are particularly        
exacting owing to their exhausting      
demands for compounds of potassium1     
phosphoric acid1 and other bodies4      
,examples of virulent and rampant       
general action are afforded by finger   
and toe in turnips1 etc41 where the     
roots are invaded by ,plasmodiophora1   
which induces hypertrophy and rotting of
 the roots2 and by the damping off of   
seedlings1 where the fungus ,pythium    
rapidly invades all parts of the        
seedlings and reduces them to a         
water-logged1 putrefying mass2 or the   
potato-disease1 which is due to the     
rapid spread of ,phytophthora in the    
leaves and throughout the plant1 which  
it blackens and rots in a few days4     
,many fungi not in themselves very      
virulent or aggressive do enormous harm 
owing to the secondary effects they     

induce4 ,some of the tree-killing       
hymenomycetes1 such as ,agaricus        
melleus1 for instance1 penetrate the    
wood of a pine at the collar1 and the   
result of the large flow of resin which 
results is to so block up the water     
passages that the tree dies off above   
with all the symptoms of drought4       
,similarly1 the ,peziza causing the     
larch disease1 having obtained access to
 the stem about a foot or so above the  
ground1 will gradually kill the cambium 
further and further round the stem1 and 
so girdle the tree as effectually as if 
we had cut out the new wood all round4  
,in all such cases--and the same applies
 to the leaf-diseases referred to       
above--the fungus may be compared to an 
army which is not strong enough to      
invade the whole territory1 but which1  
by striking at the lines of             
communication1 cuts off the supplies of 
water1 food1 etc41 and so brings the    
struggle to an end4 ,indeed we might    
compare the cases of fungi which attack 

the root and collar1 and so strike at   
and cut off the water supply1 to a      
compact army which at once cuts off the 
enemy from his narrow base2 whereas the 
innumerable units which bring about an  
epidemic attack on the leaves1 and so   
surround the enemy and cut off his food 
supplies all round1 is rather like a    
much larger army which cannot get in    
beyond the natural barriers of the      
tissues1 and so puts a cordon all round 
the territory and seizes the multitudes 
of food-stuffs at the frontiers4 ,the   
end result is similar in both cases1 but
 the methods of warfare differ4  ,many  
fungi1 however1 though they make their  
presence noticeable by conspicuous      
signs1 cannot be said to do much damage 
to the individual plant attacked4 ,the  
extraordinary malformations induced by  
parasites like ,exoascus1 which live in 
the ends of twigs of trees and stimulate
 the buds to put out dense tufts of     
shoots1 again densely                   
branched--,witches' brooms--are a case  

in point4 ,also the curious distortions 
of nettle stems swollen and curved by   
,a,ecidium1 of maize stems and leaves   
attacked by ,ustilago1 and of the       
inflorescences of ,capsella by          
,cystopus1 etc41 are not individually   
very destructive2 it is the cumulative  
effects of numerous attacks1 or of large
 epidemics1 which tell in the end4      
,some very curious effects are due to   
fungi such as ,a,ecidium elatinum1      
which1 living in the cortex of firs1    
stimulate buds to put out shoots with   
erect habit1 and with leaves which are  
radially disposed1 annually cast1 and   
differently shaped from the             
normal--characters quite foreign to the 
species of fir in its natural condition4
  ,equally strange are the shoots of    
,euphorbia infested with the aecidia of 
,uromyces1 those of bilberries affected 
with ,calyptospora1 etc4 ,in all these  
cases we must assume a condition of     
toleration1 so to speak1 on the part of 
the host1 which adapts itself to the    

altered circumstances by marked         
adaptations in its tissue developments1 
mode of growth and so forth4  ,this     
toleration is perhaps most marked in the
 case of those cereals which1 though    
infected by the minute mycelium of      
,ustilago while still a seedling1       
nevertheless go on growing as apparently
 healthy green plants indistinguishable 
from the rest1 although the fine hyphae 
of the parasite are in the tissues and  
keeping pace with the growth of the     
shoots just behind the growing points4  
,as the grains of the cereal begin to   
form and swell1 however1 the hyphae     
suddenly assume the part of a dominant  
aggressor1 consume the endosperm of the 
enlarging seed1 and replace the contents
 of the grain with the well-known black 
spores known as ,smut4   ,,notes ,,to   
,,chapter ,,xii4       ,the reader will 
find a summary of such fungi as are here
      concerned in ,massee1 ,a          
,text-,book of ,plant ,diseases1 #ahii1 
or      ,prillieux1 ,maladies des       

,plantes ,agricoles4       ,for further 
details the student should consult the  
works of      ,frank and ,sorauer       
referred to in the notes to ,chapter    
,,ix41 and      ,tubeuf1 ,the ,diseases 
of ,plants1 ,engl4 ed4 #ahig1 pp4       
#ajd-eci4       ,for experiments on the 
effects of grass on orchard trees1 see  
,report of the ,woburn ,experimental    
,fruit ,farm1 #aijj1 p4 #afj4       ,for
 the further study of weeds1 the        
interesting bulletins of      the       
,kansas ,state ,agricultural ,college1  
#ahie-ahih1 will show      the reader   
what may be done in the matter of       
classifying them      according to their
 biological peculiarities4       ,in    
regard to insects1 the reader will find 
the following list      embraces the    
subject3 ,somerville1 ,farm and ,garden 
,insects1      #ahig2 ,theobald1 ,insect
 ,life1 #ahif2 ,ormerod1 ,manual of     
,injurious ,insects1 #ahij1 and         
,handbook of ,insects ,injurious      to
 ,orchards1 etc41 #ahih4       ,the     

admirable series of publications of the 
,u4,s4 ,department of      ,agriculture 
under the editorship of ,riley and      
,howard1 and      entitled ,insect      
,life1 #ahhh-ahie1 also abounds in      
information4       ,further1            
,taschenberg's ,praktische              
,insektenkunde1 #ahgi-ahhj1      and    
,judeich and ,nietsche1 ,lehrbuch der   
,mitteleurop4 ,forst4                   
,insektenkunde1 #ahhi4       ,for an    
elementary introduction to the study of 
fungus      diseases1 see ,marshall     
,ward1 ,diseases of ,plants1 ,soc4 for  
,promoting ,christian ,knowledge1       
,london4     ,,chapter ,,xiii4  ,,nature
 ,,of ,,disease4       ,general and     
local disease--,general death owing to  
cutting-off      supplies1              
etc4--,disease of                       
organs--,tissue-diseases1 e4g4          
timber--,root-diseases--,leaf-diseases1 
etc4--,diseases of      ,respiratory1   
,assimilatory1 and other                
organs--,physiological and              

,parasitic diseases--,pathology of the  
cell--,cuts--,cork--,callus             
--,irritation--,stimulation by          
protoplasm--,hypertrophy4   ,on going   
more deeply into the nature of those    
changes in plants which we term         
pathological or diseased1 it seems      
evident that we must at the outset      
distinguish between various cases4 ,a   
plant may be diseased as a whole because
 all or practically all its tissues are 
in a morbid or pathological condition1  
such as occurs when some fungus invades 
all the parts or organs--e4g4 seedlings 
when completely infested by ,pythium1 or
 a unicellular ,alga when invaded by a  
minute parasite2 or it may die          
throughout1 because some organ with     
functions essential to its life is      
seriously affected--e4g4 the roots are  
rotten and cannot absorb water with     
dissolved minerals and pass it up to the
 shoot1 or all the leaves are infested  
with a parasite and cannot supply the   
rest of the plant with organic food     

materials1 in consequence of which parts
 not directly affected by any malady    
become starved1 dried-up1 or poisoned or
 otherwise injured by the results or    
products of disease elsewhere4  ,in a   
large number of cases1 however1 the     
disease is purely local1 and never      
extends into the rest of the organs or  
tissues--e4g4 when an insect pierces a  
leaf at some minute point with its      
proboscis or its ovipositor1 killing a  
few cells and irritating those around so
 that they grow and divide more rapidly 
than the rest of the leaf tissues and   
produce a swollen hump of tissue1 or    
gall2 or when a knife-cut wounds the    
cambium1 which forthwith begins to cover
 up the dead cells with a similarly     
rapid growth of cells1 the callus4      
,numerous minute spots due to fungi on  
leaves1 cortex1 etc41 are further cases 
in point1 the mycelium never extending  
far from the centre of infection4  ,many
 attempts have been made to classify    
diseases on a basis which assumes the   

essential distinction of the above      
cases1 and we read of diseases of the   
various organs--root-diseases1          
stem-diseases1 leaf-diseases1 and so    
forth2 or of the various                
tissues--timber-diseases1 diseases of   
the cambium1 of the bark1 of the        
parenchyma1 and so on4 ,furthermore1    
attempts have been made to speak of     
general functional disease1 of diseases 
of the respiratory organs1 of the       
absorptive organs1 and so forth1 as     
opposed to local lesions4  ,critical    
examination1 however1 shows that no such
 distinctions can be consistently       
maintained1 partly because the organs   
and functions of plants are not so      
sharply marked off as they are in       
animals1 the diseases of which have     
suggested the above classification1 and 
partly because all disease originates in
 the cells and tissues1 and it is a     
matter of detail only that in some      
cases--e4g4 severe freezing or drought  
of seedlings1 or when some ingredient is

 wanting in the soil--the diseased      
condition affects practically every cell
 alike from the first1 while in others  
it spreads more or less rapidly from    
some one spot4  ,even the distinction   
into physiological diseases versus      
parasitic diseases cannot be maintained 
from the standpoint of the nature of the
 disease itself4 ,all disease is        
physiological in so far as it consists  
in disturbance of normal physiological  
function1 for pathology is merely       
abnormal physiology1 no matter how it is
 brought about4 ,this is not saying that
 no importance is to be attached to the 
mode in which disease is incurred or    
induced3 it is merely insisting on the  
truth that the disease itself consists  
in the living cell-substance--the       
protoplasm--not working normally as it  
does in health1 and this1 whether want  
of water1 minerals1 or organic food be  
the cause1 or whether the presence of   
some poison or mechanical irritant be   
the disturbing agent1 as also whether   

such want or irritation be due to some  
defect in soil or air1 or to the ravages
 of a fungus or an insect4  ,this being 
understood ,i need not dwell on the     
common fallacy of confounding the       
fungus1 insect1 soil or other agent with
 the disease itself1 or of making the   
same blunder in confusing symptoms with 
maladies4 ,in this sense1 wheat rust is 
not a disease3 it is a symptom which    
betrays the presence of a               
disease-inducing fungus1 the ,rust      
fungus4 ,similarly1 chlorosis is not a  
disease3 it is a symptom of imperfect   
chlorophyll action1 and the best proof  
of the truth of both statements is that 
in both cases the fundamental           
disease-action is the starvation of the 
cell-protoplasm of carbohydrates and    
other essential food matters--in the one
 case because the fungus steals the     
carbohydrates as fast as the leaves can 
make them1 in the second because the    
leaf is unable to make them4  ,the      
foundation of a knowledge of disease in 

plants therefore centres in the         
understanding of the pathology of living
 cells4  ,if a suitable mass of living  
cells is neatly cut with a sharp razor  
the first perceptible change is one of  
colour3 the white flesh of a potato or  
an apple1 for instance1 turns brown as  
the air enters the cut cells1 and the   
microscope shows that this browning     
affects cell-walls and contents alike4  
,the cut cells also die forthwith2 and  
the oxygen of the air combining with    
some of their constituents forms the    
brown colouring matter which soaks into 
the cell-walls4 ,the uninjured cells    
below them grow longer1 pushing up the  
dead debris1 and divide across by walls 
parallel to the plane of the wound1 and 
so form series of tabular cells with    
thin walls1 which also soon turn brown  
and die1 the cell-walls meanwhile       
undergoing changes which convert them   
into cork4 ,the living cells deeper down
 are now shut off from the outer world  
by a skin1 of several layers1 of        

cork-cells1 which prevent the further   
free access of air or moisture4 ,during 
the period of active cell-division which
 initiates the cork1 the temperature of 
the growing cells rises3 a sort of fever
 7wound-fever7 is induced1 evidently    
owing to the active respiration of the  
growing cells4  ,this healing by cork   
occurs in any tissue of living cells    
exposed by a cut--leaf-tissue1 young    
stem or root1 fruit1 cambium1 etc42 and 
the same applies to any other kind of   
cutting or tearing injury--such as a    
prick with a needle or the proboscis of 
an insect1 a stripping1 or even a       
bruise4  ,such healing is prepared for  
and carried out very thoroughly in the  
case of falling leaves and cast         
branches1 the plane of separation being 
covered by a cicatrix of cork4  ,if the 
cell-tissue under the wound is actually 
growing at the time1 however1 a further 
process is observed when the wound-cork 
has been formed4 ,the uninjured cells   
below go on growing outwards more       

vigorously than ever1 the pressure of   
the overlying tissues taken off by the  
cut having been removed1 and1 lifting up
 the cork-layer as they do so1 they     
rapidly divide into a juicy mass of     
thin-walled cells which is of a         
cushion-like nature and is termed a     
,callus4 ,this callus is at first a     
homogeneous tissue of cells which are   
all alike capable of growing and        
dividing1 but in course of time it      
undergoes changes in different parts    
which result in the formation of        
tracheids1 vessels1 fibres and other    
tissue-elements1 and even organs1 just  
as the embryonic tissues of the growing 
points1 cambium1 etc41 of the healthy   
plant give origin to new growths4 ,such 
wound-wood1 however1 is apt to differ   
considerably in the arrangement1        
constitution and hardness of its parts  
as compared with normal wood1 and its   
peculiar density and cross-graining are 
often conspicuous4  ,if instead of a    
simple tissue1 the cut or other wound   

lays bare a complex mass such as wood1  
the resultant changes are essentially   
the same to start with4 ,the living     
cells bordering the wound form cork1 and
 then those deeper down grow out and    
form a callus4 ,the exposure of the wood
 however1 entails alterations in its    
non-living elements also4 ,the lignified
 walls of tracheids1 fibres1 etc41 turn 
brown to a considerable depth1 and this 
browning seems to be--like all such     
discolorations in wounds--due to        
oxidation changes in the tannins and    
other bodies present3 the process is    
probably similar to what occurs in      
humification and in the conversion of   
sap-wood into heart-wood in trees4 ,such
 wood is not merely dead1 but it is also
 incapable of conveying water in the    
lumina of its elements1 which slowly    
fill with similarly dark-coloured1      
impervious masses of materials termed   
wound-gum1 the nature of which is       
obscure1 but which slowly undergoes     
further changes into resin-like         

substances4  ,the exposure of wood by a 
wound results also in another mode of   
stopping up the vessels and so hindering
 the access of air1 loss of water1 etc41
 for the living cells of the medullary  
rays and wood-parenchyma grow into the  
lumina of the larger vessels through the
 pits1 forming thyloses1 again a        
phenomenon met with in heart-wood4 ,in  
,conifers the stoppage of the lumina is 
increased by deposition of resin1 which 
also soaks into the cell-walls and the  
wounded wood becomes semi-translucent   
owing to the infiltration4  ,every      
living cell in an active condition is   
irritable1 and one of the commonest     
physiological reactions of growing      
tissues is that of responding to the    
touch of a resistant body1 as is vividly
 shown by the movements of the          
,sensitive plant1 ,dionaea1 etc41 and by
 those of tendrils1 growing root tips1  
etc41 on careful observation4 ,we have  
reason for stating that if a minute     
insect1 too feeble to pierce the        

cuticle1 cling on to one side of the    
dome-shaped growing point of any shoot1 
the irritation of contact of its claws1 
hairs1 etc41 would at once cause the    
protoplasm of the delicate cells to     
respond by some abnormal behaviour2 and1
 as matter of experiment1 ,darwin showed
 long ago that if a minute piece of     
glass or other hard body is kept in     
contact with one side of the tip of a   
root1 the growth on the side in contact 
is interfered with4 ,moreover we know   
from experiments on heliotropism1       
thermotropism1 etc41 that even          
intangible stimuli such as rays of      
light1 etc41 impinging unsymmetrically  
on these delicate cells cause           
alterations in their behaviour--e4g4    
arrest or acceleration of growth4       
,perhaps the most remarkable class of   
stimulations1 however1 is that due to   
the presence of the entire protoplasmic 
body of one organism in the cell of     
another1 each living its own life for   
the time being1 but the protoplasm of   

the host cell showing clearly1 by its   
abnormal behaviour1 that the presence of
 the foreign protoplasm is affecting its
 physiology4 ,a simple example is       
afforded by ,zopfs' ,pleotrachelus1 the 
amoeboid protoplasmic body of which     
lives in the hypha of ,pilobolus1       
causing it to swell up like an inflated 
bladder1 in which the parasite then     
forms its sporangia4 ,the ,pleotrachelus
 does not kill the ,pilobolus1 but that 
its protoplasm alters the metabolic     
physiology of the latter is shown by the
 hypertrophy of the cells1 and by the   
curious fact that it stimulates the     
,pilobolus to form its sexual           
conjugating cells1 otherwise rare1 an   
indication of very far-reaching         
interference with the life-actions of   
the host4  ,an equally remarkable       
example is that of ,plasmodiophora1 the 
amoeboid naked protoplasm of which lives
 and creeps about in the protoplasm of a
 cell of the root of a turnip1 to which 
it gains access through the root-hairs4 

,it does not kill the cell1 but         
stimulates its protoplasm to increased  
activity and growth and division1 itself
 dividing also and passing new amoebae  
into each new daughter-cell of the host4
 ,here the processes of stimulation1    
hypertrophy and further division are    
repeated1 until hundreds or thousands of
 the turnip root-cells are infected4    
,the externally visible result is the   
formation of distorted swellings on the 
root 7,finger and ,toe71 most of the    
cells of which are abnormally large and 
filled with amoeboid ,plasmodiophora    
protoplasm1 which finally devours the   
turnip-protoplasm and itself passes over
 into spores4 ,here we have most        
convincing proof of the stimulation of  
protoplasm by other protoplasm in direct
 contact with it2 and that the          
metabolism of the host-cells is         
profoundly altered is shown not only by 
the abnormal growth of the cells1 but   
also by the starvation of the rest of   
the turnip plant as the ,plasmodiophora 

gets the upper hand4 ,we have here1 in  
fact1 a local intracellular parasitic   
disease1 gradually invading large tracts
 of tissue and eventually inducing      
general disease resulting in death--a   
state of affairs reminding us of cancer 
in animals4  ,irritation and hypertrophy
 of cells1 however1 may be induced by   
parasites which never bring their       
protoplasm into direct contact with that
 of the host4 ,many ,chytridiaceae      
penetrate the cells of plants1 and grow 
inside them as short tubes1 vesicles1   
etc41 the protoplasm of which is        
separated by their own cell-walls from  
that of the host-cell2 nevertheless     
hypertrophy and abnormal cell-divisions 
and secretions are induced1 and the     
effect even extends to neighbouring     
cells--e4g4 ,synchytrium--showing that  
some influence is exerted through cells 
themselves not directly affected4 ,this 
latter point need not surprise us now we
 know that the cells of plant-tissues   
are connected by fine protoplasmic      

strands passing through the separating  
cell-walls4  ,but the invading plant    
need not actually enter the cells1 and  
may still stimulate them through both   
its own and their own cell-walls to     
abnormal growth4 ,this is well shown by 
the intercellular mycelium of ,exoacus  
and ,exobasidium1 and the latter affords
 an excellent illustration of the       
far-reaching effects of hyphae on the   
cells 7of ,vaccinium7 into which they do
 not penetrate4 ,not only are the cells 
stimulated to grow larger and divide    
oftener than normally1 thus producing   
large gall-like swellings1 but the      
chlorophyll disappears1 the cell sap    
changes colour to red1 the numerous     
compound crystals normally found in the 
tissues diminish in number and are      
different in shape1 large quantities of 
starch are stored up1 and even the      
vascular bundles are altered in         
character4 ,all these changes indicate  
very profound alterations in the        
physiological working of the protoplasm 

of the cells of the host1 and yet the   
fungus has done its work through both   
its own cell-walls and those of the     
host4  ,even harmless endophytic algae  
in the intercellular spaces of plants   
may stimulate the cells in their        
immediate neighbourhood to increased    
growth1 e4g4 ,anabaena in the roots of  
,cycads4   ,,notes ,,to ,,chapter       
,,xiii4       ,with reference to        
cork-healing and wound-fever the student
 may      consult ,shattock ,on the     
,reparative processes which occur in    
,vegetable ,tissues1 ,journal of the    
,linnean ,society1 #ahhb1      ,vol4    
,,xix41 p4 #a2 and ,shattock ,on the    
,fall of ,branchlets in      the ,aspen1
 ,journal of ,botany1 #ahhc1 ,vol4      
,,xxi41 p4 #cjf4 ,also      ,richards1  
,the ,respiration of ,wounded ,plants1  
,annals of      ,botany1 ,vol4 ,x41     
#ahif1 p4 #eca2 and ,the ,evolution of  
,heat by      ,wounded ,plants1 ,ann4 of
 ,bot41 ,vol4 ,,xi41 #ahig1 p4 #bi4     
,for details and figures respecting     

callus1 see ,sorauer1      ,physiol4 of 
,plants1 p4 #age4       ,in respect to  
the irritable movements referred to see 
,darwin1      ,the ,power of ,movements 
in ,plants1 #ahhj1 chapter ,,iii4 ,the  
recent work of ,nawaschin1              
,beobachtungen ueber den feineren       
,bau u4 ,umwandlungen von               
,plasmodiophora1 ,flora1 ,vol4          
,,lxxxvi41      #ahii1 p4 #djd1 should  
be read for details and literature      
concerning ,finger and ,toe4            
,,chapter ,,xiv4  ,,nature ,,of         
,,disease 7,continued74       ,actions  
of poisons in small doses--,results of  
killing a few                           
cells--,malformation--,enzymes--,secreti
ons and excretions--      ,acids1       
poisons1 etc4--,chemotactic             
phenomena--,parasitism--      ,epiphytes
 and endophytes--,symbiosis--,galls4    
,physiological research has shown that  
the respiratory activity of cells may be
 increased by small doses of poisons1   
and even that growth may be accelerated 

by them--e4g4 chloroform1 ether--and1   
still more remarkable1 that fermentative
 activity may be enhanced by minute     
doses of such powerful mineral poisons  
as mercuric chloride1 iodine salts1     
etc41 and that the cells may be         
gradually accustomed to larger doses    
without injury4 ,unfertilised eggs of   
insects have been started into growth by
 treatment with acids and those of frogs
 with mercury salts1 and the germination
 of beans quickened by various poisonous
 alkaloids4 ,in other words1 graduated  
doses of poison may alter the           
physiological activity of living cells1 
inducing pathological phenomena1 while  
larger doses kill them4  ,now we know at
 least one parasitic fungus which       
poisons the cells of its host1 and kills
 them1 with similar symptoms to those   
resulting from excessive doses of the   
above-named toxic agents4 ,botrytis     
hyphae1 living in the cell-walls of     
plants1 but not entering the cells1     
excretes a poison which kills the       

protoplasm1 and the fungus then feeds on
 the debris4 ,numerous other fungi form 
powerful poisons1 but we do not know    
whether or how they employ them--e4g4   
,ergot4  ,it is obvious that if all the 
young cells of a root-tip or of the apex
 of a shoot1 or those of a young leaf1  
are growing and dividing regularly1 the 
killing of one or a few cells at one    
point on the side of the organ must     
result in irregularities--in            
malformation--of the adult organ4 ,this 
has been proved experimentally by       
destroying a few cells with a needle4   
,it can also be done by planting a      
minute mycelium of ,botrytis laterally  
on a young organ--e4g4 a very young     
lily-bud4 ,the fungus adheres to the    
surface1 kills a few epidermis cells1   
and forms a foxy-red spot1 which becomes
 concave as the dead cells lose water   
and dry4 ,since the rest of the bud goes
 on growing1 however1 while this dead   
point remains stationary1 the latter    
gradually becomes the centre of a       

concavity1 the growing tissues having   
grown round it3 the bud is deformed4    
,numerous cases of malformed organs are 
explained in this way2 a minute insect  
has bitten or pierced the young tissue1 
or a fungus has killed a minute area1 or
 a drop of acid condensed from fumes in 
the air is the lethal agent1 and so     
forth4 ,and even on a much larger scale 
we see the same kinds of agents at work4
 ,wherever a patch of cells is killed   
whilst those around go on growing1 there
 must result some deformation of the    
resulting organ1 since had the injury   
been withheld the number and sizes of   
the cells now fixed in death would have 
increased and covered a larger area3    
they now serve to pull over to their    
side the still living and growing cells4
 ,the same results follow on any lateral
 wound3 the killed spot of tissue serves
 as a point round which the continued   
growth of other parts of the organ      
turns4 ,hence the malformation is in    
these cases a secondary effect1 and not1

 as in simple hypertrophy1 a direct     
effect of the action of the cells       
involved in the injury4  ,there is      
another class of bodies secreted by     
fungi1 however1 which act directly on   
cells1 viz4 enzymes--that is1 soluble   
bodies which are able to dissolve       
cellulose 7cytases71 starch 7diastases71
 proteids 7proteolytic enzymes71 and    
other substances1 by peculiar           
alterations in their constitution4 ,it  
is by means of its cytase that ,botrytis
 hyphae pierce the cellulose walls of   
plants1 and no doubt in all cases where 
fungi pierce cell-walls it is by the    
solvent action of such a cytase1 and    
similarly when haustoria penetrate into 
the cells4 ,it is also by means of these
 starch-dissolving enzymes 7diastases7  
and proteolytic enzymes1 etc41 that the 
hyphae inside the cells are enabled to  
make use of the starch1 proteids1 etc41 
they find there4  ,all living cells form
 materials1 resulting from the activity 
of the protoplasm1 which we may compare 

with the refuse or by-products formed in
 any great manufacturing industry3 these
 by-products have to be got rid of if   
they are injurious or noisome           
7excretions71 and if not--i4e4 if they  
are capable of further use              
7secretions7--they have to be stored    
away till required4 ,some of the most   
prominent of these bodies excreted by   
fungi are1 as we have seen1 poisonous   
acids1 such as oxalic acid1 enzymes1 and
 organic poisons1 such as those in      
ergot4 ,but similar enzymes1 acids1     
poisons1 etc41 to those found in fungi  
are also found in the cells of other    
plants and animals2 for only by means of
 their solvent actions can processes    
like digestion and assimilation of the  
starchy and other materials into the    
body-substance be accomplished1 and we  
have seen that it is a general property 
of living cells to form acids1 and other
 excretions and secretions4  ,now we    
know very little about what may happen  
when an organism--say a                 

fungus--secreting especially one kind of
 enzyme or poison or other active       
substance1 comes into intimate contact  
with another--say a leaf-cell--which    
secretes predominantly others1 but what 
we do know points to the certainty that 
various complications will occur4  ,for 
instance1 if certain bacteria which     
prefer an alkaline medium1 and yeasts   
which prefer an acid environment are    
mixed in a saccharine solution1 it      
depends on the reaction of the liquid   
which organism gains the upper hand3 if 
the liquid is acid the yeast may        
dominate the bacteria2 if alkaline it   
may be suppressed by them4  ,that a     
parasite may be prevented from          
successfully attacking a particular     
plant is shown by the failure of        
,cuscuta to establish its haustoria in  
poisonous plants such as ,euphorbia1    
,aloe1 etc41 and it has been pointed out
 that poisonous secretions in the cells 
of the plant protect them against the   
penetration of fungi4 ,this cannot be   

taken as meaning that any poison        
protects against any parasite1 however1 
for ,euphorbia is itself subject to     
attacks of ,uredineae1 and ,pangium     
edule1 which contains prussic acid and  
is extremely poisonous to most animals1 
is eaten with avidity by several        
insects1 while nematode worms can live  
in its tissues4 ,this is no more        
remarkable1 however1 than the fact that 
,fontaria1 a myriapod1 secretes prussic 
acid in its own tissues1 or than that   
certain glands of the stomach secrete   
free hydrochloric acid1 and ,dolium     
forms sulphuric acid in its glands4     
,there is yet a further point to notice 
here4 ,it has been proved that certain  
substances formed in plant-cells1 not   
necessarily nutritive1 attract the      
hyphae of parasitic fungi or repel them1
 according to the kind and degree of    
concentration4 ,so clear has this proof 
been made that it was possible in       
experiments conducted apart from a host 
plant1 to make the hyphae on one side of

 an artificial membrane--e4g4           
collodion--penetrate it by placing one  
of these attractive 7chemotropic7       
substances in suitable proportions on   
the other side4 ,the hyphae dissolved   
holes in the membrane by means of       
enzymes and plunged into the attractive 
substance on the other side4  ,the      
foregoing sketch gives us a glimpse into
 the causes at work in parasitism4      
,suppose a fungus on the outside of the 
epidermis of a young organ--say a leaf4 
,it may be unable to penetrate into the 
plant1 and finding no suitable food     
outside it dies3 or it may be satisfied 
with the traces of organic matter on the
 epidermis and then lives the life of a 
saprophyte4 ,or it may be able to       
establish a hold-fast on the tender     
epidermal surface1 but without entering 
the cells1 and irritate the developing  
organ by contact stimulation1 inducing  
slight abnormalities2 if in its further1
 purely superficial growth such an      
epiphyte covers large areas of the leaf1

 and especially if the hyphae are dark  
coloured--e4g4 ,dematium and other      
,sooty ,moulds--injury may be done to   
the leaf owing to the shading action    
which deprives the chlorophyll below of 
its full supply of solar energy4 ,some  
epiphytes1 however1 are able to fix     
their hyphae to the epidermis by sending
 minute peg-like projections into the   
cuticle--,trichosphaeria1               
,herpotrichia--while others send        
haustoria right through the outer       
epidermal walls--e4g4 ,erysiphe--and    
thus supplement mere contact-irritation 
and shading by actual absorption from   
the external cells4 ,here the fungus is 
a parasitic epiphyte4  ,a stage further 
is attained in those fungi which enter  
the stomata and live in the             
intercellular spaces--e4g4 many         
,uredineae and ,phytophthora--and many  
such intercellular endophytes increase  
their attack on the cells by piercing   
their walls with minute 7,cystopus7 or  
large and branched 7,peronospora7       

haustoria1 or even eventually pierce the
 cells and traverse them bodily         
7,pythium74 ,in all these cases it is   
clear that conflicts must occur between 
poison and antidote1 acid and alkali1   
attractive and repellent substances1    
enzyme and enzyme1 etc41 as was hinted  
at above2 and the same must take place  
when the parasite is endophytic and     
intracellular from the first1 as in     
,chytridiaceae1 etc41 the zoospores of  
which pierce the outer cell-walls and   
forthwith grow into the cells4 ,there   
are also fungi which1 while able to     
pierce the outer cell-walls1 and grow   
forward in the thickness of the wall    
itself1 cannot enter the living cells   
themselves--e4g4 ,botrytis4 ,in the     
example mentioned1 the fungus excretes a
 poison1 oxalic acid1 which soaks into  
and kills the cells next its point of   
attack3 into these dead cells it then   
extends1 and1 invigorated by feeding on 
them1 extends into other cell-walls and 
excretes more poison1 and so on4  ,on   

the basis of the foregoing it seems     
possible to sketch a general view of the
 nature of parasitism4 ,in order that a 
fungus may enter the cells it must be   
able to overcome not only the resistance
 of the cell-walls1 but that of the     
living protoplasm also3 if it cannot do 
the latter it must remain outside1 as a 
mere epiphyte1 or at most an            
intercellular endophyte4 ,if it can do  
neither it must either content itself   
with a saprophytic existence or fail1 so
 far as that particular host-plant is   
concerned4 ,its inability to enter may  
be due to there being no chemotropic    
attraction1 or to its incapacity to     
dissolve the cell-walls1 or to the      
existence in the cell of some           
antagonistic substance which neutralises
 its acid secretions1 destroys its      
enzymes or poisons1 or is even directly 
poisonous to it4  ,moreover when once   
inside it does not follow that it can   
kill the cell4 ,the protoplasm of the   
latter may have been unable to prevent  

the fungus enemy from breaking through  
its first line of defence--the          
cell-wall1 but it may be quite capable  
of maintaining the fight at close       
quarters1 and we see signs of the       
progress of the struggle in hypertrophy1
 accumulation of stores1 and other      
changes in the invaded cells and their  
contents4  ,finally1 the invested or    
invaded cell may so adapt itself to the 
demands of the invader that a sort of   
arrangement is arrived at by which life 
in common--,symbiosis--is established1  
each organism doing something for the   
other and each taking something from the
 other4 ,in this latter case1 which is  
often realised--e4g4 lichens1 leguminous
 plants and the organisms in their      
root-nodules1 mycorrhiza1 etc4--we leave
 the domain of disease1 which supervenes
 indeed if the other symbiont is        
lacking4  ,some interesting facts       
bearing on the matters here under       
discussion1 have been obtained from the 
study of ,galls1 the curious outgrowths 

found on many plants and due to the     
action of insects4  ,a typical gall     
exhibits three distinct and             
characteristic layers of tissue         
surrounding the hollow chamber in which 
the larva of the insect lies1 viz41 an  
outer layer of soft cells forming a     
parenchyma covered with an epidermis1   
and frequently also with a layer of     
cork2 an inner stratum consisting of    
very thin-walled delicate cells filled  
with protoplasmic and reserve           
food-materials on which the larva feeds2
 and between the two a more or less     
definite layer of thick-walled          
sclerenchyma cells which serve as a     
protection against accidents to the     
larva as the outer layer shrivels or    
rots1 or if it is exposed to the attack 
of marauders4 ,this layer may be absent 
from galls which have a short life only4
 ,vascular bundles run into the outer   
layer from the leaf-veins or the stele  
of the shoot1 etc4 ,such galls abound in
 tannin1 and are frequently of use in   

the arts on this account3 they also     
contain starch1 and proteid substances  
and crystals of calcium oxalate4 ,when  
the larva has consumed the stores of    
food material and reached the adult     
stage it eats its way out and escapes4  
,the growth of such a gall is preceded  
by the laying of an egg on or in the    
embryonic tissue of a leaf1 stem1 or    
other young part1 and it is interesting 
to note that only organs in the         
meristematic stage can form galls1 and  
that it is by no means necessary that   
the tissues should be wounded4          
,moreover1 the egg as such is incapable 
of stimulating the plant tissues1 but   
when it hatches1 the resulting larva1   
beginning to feed on the cells1         
irritates the tissues and rapid growth  
and cell-division occur1 as in the case 
of other wounds or of fungus attacks4   
,the actual wound made by the ovipositor
 heals up at once4 ,it is evident from  
numerous recent researches that these   
true galls are not due to any poisonous 

or irritating liquid injected by the    
parent1 but that the stimulus to the    
tissue formation is similar to that     
exerted by a wound4 ,the young gall is  
in fact a callus enclosing the living   
larva1 and it is the continued          
irritation of the latter which keeps up 
the stimulation4 ,the final shape and   
constitution of the gall depend on      
mutual reactions--not as yet explained  
in detail--between the species of plant 
and the species of gall-insect          
concerned1 as may readily be seen from  
the extraordinary variations in size1   
shape1 colouring1 hairiness and other   
structural peculiarities of the galls on
 one species of1 for instance1 the      
common oak4 ,from what we have learnt   
about fungus parasites1 however1 there  
can be little doubt that reactions      
between the cells and the larva of the  
insect occur1 resembling those which    
take place between the cells and the    
hyphae of the fungus1 and this is borne 
out by the study of other hypertrophies 

due to animals2 e4g4 ,nematode worms in 
roots1 and the remarkable galls--the    
simplest known--on ,vaucheria1 caused by
 the entrance into this alga of a       
species of ,notommata1 which induces a  
different gall on each of the various   
species of its host plants4  ,it must be
 concluded that the formation of the    
,vaucheria gall is induced by the       
mechanical irritation which the ,rotifer
 causes in the protoplasm4 ,these galls 
are comparable to the hypertrophies in  
,pilobolus caused by the presence of    
,pleotrachelus4  ,attempts to induce the
 development of galls artificially by   
injecting formic1 acetic and other      
vegetable acids1 poisons and other      
substances into the tissues have1       
however1 failed1 and even the substances
 contained in the insect or gall itself 
only produced negative results4 ,nothing
 further was obtained than slight callus
 formations in some cases4 ,nor have    
experimenters succeeded in obtaining    
more than slight distortions by fixing  

insects on the growing leaves in such   
positions that they could scratch the   
epidermis4  ,we must therefore conclude 
that very complex interactions between  
the plant and insect are here concerned1
 among which may be the infiltration of 
some liquid from larva to plant--many of
 these gall larvae are strongly scented1
 and ,kustenmacher says that fluids     
excreted by the larva are absorbed by   
the gall-tissue apparently as nutriment4
 ,this would point to the symbiotic     
character of galls and their guests4    
,,notes ,,to ,,chapter ,,xiv4           
,with regard to the action of poisons in
 small doses see      further           
,johannsen1 ,das ,aether-,verfahren beim
 ,fruhtreiben1      ,jena1 #aijj1 and1  
for ,botrytis1 see ,marshall ,ward1 ,a  
,lily      ,disease1 ,annals of ,botany1
 ,vol4 ,,ii41 #ahhi1 p4 #chh4       ,the
 subject of enzymes has been            
exhaustively treated by ,green1         
,the ,soluble ,ferments and             
,fermentations1 ,cambridge1 #ahii1 to   

which the reader is referred for        
literature4 ,i have taken the           
statements regarding ,fontaria and      
,dolium from ,kassowitz1                
,allgemeine ,biologie1 p4 #ahb4 ,the two
 most important works on                
chemotactic phenomena are ,pfeffer1     
,uber ,chemotaktische      ,bewegungen1 
etc41 ,unters4 aus dem ,bot4 ,inst4 zu  
,tubingen1      ,b4 ,,ii41 p4 #ehb1 and 
,miyoshi1 ,die ,durchbohrung von        
,membranen      durch ,pilzfaden1       
,pringsh4 ,jahrb4 f4 ,wiss4 ,bot41 ,b4  
,,xxviii41      #ahie1 p4 #bfi1 and from
 these the further literature can be    
traced4 ,as regards the nature of       
parasitism see ,marshall ,ward1      ,on
 ,some ,relations between ,host and     
,parasite1 etc41 being the              
,croonian ,lecture delivered before the 
,royal ,society1 ,proc4      ,roy4      
,soc41 ,vol4 #dg1 p4 #cic4 ,on          
,symbiosis1 see ,marshall ,ward1        
,symbiosis1 ,annals of ,botany1 #ahii1  
,vol4 ,,xiii41 p4 #edi1      where the  

literature is collected4 ,for a general 
account of      galls the reader may    
consult ,kerner1 ,the ,natural ,history 
of      ,plants1 ,eng4 ed41 #ahie1 ,vol4
 ,,ii41 pp4 #ebg-eed1 and ,adler1       
,alternating ,generations1 ,a           
,biological ,study of ,oak ,galls1      
etc41 #ahid4     ,,chapter ,,xv4        
,,spreading ,,of ,,disease ,,and        
,,epidemics4       ,dissemination of    
fungi by the aid of snails1 rabbits1    
bees1      and                          
insects--,man--,distribution in soil1 on
 clothes1 through      the post1        
etc4--,worms1 wind--,puffing of         
spores--,creeping of                    
mycelia--,lurking parasites--,spread of 
insects and other      animals--,losses 
due to epidemics4   ,the dissemination  
of plant diseases is a subject which has
 been far too much neglected1 but our   
knowledge of it is slowly increasing4   
,the spores of fungi such as ,rusts and 
,erysipheae are often carried from plant
 to plant by snails2 those of           

root-destroying and tree-killing        
,polyporei by rabbits1 rats1 and other  
mammals which rub their fur against the 
hymenophores4 ,bees have been shown to  
carry the spores of ,sclerotinia and    
infect the stigmas of ,bilberries1 etc41
 with them2 and flies convey the conidia
 of ,ergot from grain to grain4         
,insects1 indeed1 of all kinds are great
 disseminators of disease--as witness   
also the part played by mosquitoes in   
transferring the malaria parasite to    
man--and beetles1 bees1 flies1 etc41 of 
all sorts probably play more active     
parts in this work than has yet been    
proved1 since they not only carry spores
 attached like pollen to their hairy    
bodies1 but in many cases in their      
alimentary canal1 to be spread later in 
the dung4  ,the part played by man in   
conveying fungi from plant to plant     
counts for much4 ,not only do gardeners 
and farm labourers carry spores on their
 boots and clothes as they pass from    
infected to non-infected areas1 but     

carted soil and manure are frequently   
infested with spores of ,smuts1         
,fusarium1 ,polyporus1 and the sclerotia
 or rhizomorphs of ,sclerotinia1        
,agaricus melleus1 ,dematophora1 etc4   
,man also sends diseases through the    
post1 and by rail and ship1 by spores or
 mycelia attached to seedlings1 bulbs1  
fruits1 flowers1 etc41 as shown in      
several cases of potato1 vine1          
hollyhock1 lily1 and hyacinth diseases4 
,every time a carpenter saws a piece of 
fresh timber with the saw which has been
 used previously for cutting wood       
attacked with dry rot1 he risks         
infecting it with the fungus4 ,similarly
 in pruning3 every cut with a knife     
which the gardener has used on infected 
branches may infect the tree4  ,cuttings
 made with a soil-contaminated knife and
 stuck into ordinary soil in dirty boxes
 covered with equally dirty glass1      
present every chance for infection by   
soil organisms2 bacteria and fungi      
obtain access to the vessels1 and derive

 plenty of food from the juices1 and the
 wonder is not that so many cuttings    
damp off1 but that any are raised at all
 under ordinary conditions4  ,that worms
 bring buried spores to the surface can 
hardly be doubted after ,pasteur's      
experiments with ,anthrax1 and the      
principle of ,darwin's discoveries of   
the important bearing of the habits of  
earthworms on this subject1 and that the
 soil attached to the feet of ducks and 
other birds teems with small seeds1     
applies to fungi also4 ,wind is also    
responsible for distributing            
fungus-spores over wide areas1 as may be
 easily proved by fixing a glass slide  
smeared with glycerine in the course of 
a breeze passing over an infected area4 
,but although the fungi are1 generally  
speaking1 passive in regard to their    
distribution1 such is by no means always
 the case4 ,apart from the fact that    
some forms attract insects by means of  
honey dew 7,ergot71 or by sweet odours  
7,spermogonia1 ,sclerotinia71 the       

zoospores of ,pythium1 ,phytophthora1   
etc41 are motile1 and although they     
cannot move far in the films of water in
 which they travel1 nevertheless in a   
wet potato field1 with the wind flapping
 the leaves one against the other1 some 
dissemination of importance must be     
actively brought about1 and similarly   
with the amoebae of ,plasmodiophora in  
the soil4  ,the shooting of ascospores  
into the air by certain species of      
,peziza1 from the discs of which the    
spores may be seen to puff out in       
clouds1 affords further evidence that   
fungi cannot be regarded as entirely    
passive in respect to distribution of   
their spores4 ,but when we come to      
certain of the soil fungi--e4g4         
,agaricus melleus1 ,dematophora1        
etc4--the active creeping forward by    
growth in the soil of their rhizomorphs 
and mycelial strands afford examples of 
active spreading of considerable        
importance in the vineyard and forest1  
since they pass from root to root and   

from tree to tree and may infect the    
entire area in course of time4  ,not the
 least significant mode of dissemination
 is that by which what ,i have termed   
lurking parasites are spread3 such are  
fungi which attach themselves to the    
seeds1 fruits1 tubers1 etc41 of other   
plants and so obtain all the advantages 
of being carried and sown with the      
latter--e4g4 ,ustilagineae and          
,uredineae which adhere to grain1       
,verticillium1 ,nectria1 etc41 in       
potatoes and other plants4  ,the spread 
of diseases due to animals1 especially  
insects1 is of course more active1 in   
consequence of the motility of the      
distributing agents4 ,this is most      
marked in the winged species1 of which  
locusts1 beetles1 moths and butterflies1
 flies and wasps furnish well-known     
examples2 and is not inconsiderable in  
the case of wingless and merely creeping
 species4 ,it is noteworthy that many   
forms wingless in the parasitic stage   
are winged at certain periods1 e4g4 the 

females of ,phylloxera4  ,that man also 
spreads insect pests is well known and  
acted upon1 as witness the phylloxera   
laws--which1 however1 it is to be feared
 too often only illustrate once more the
 adage concerning the shutting of the   
stable door after the horse has gone4   
,it would be tedious to attempt anything
 like a complete account of the         
estimates of loss in different          
countries1 due to the ravages of insects
 and fungi1 but the following examples  
should surely serve to convince anyone  
of the magnitude of these losses and of 
the economic importance of the whole    
question1 and the reader may be referred
 to the special literature for further  
details4  ,the coffee leaf-disease of   
,ceylon1 due to the fungus ,hemileia1 is
 estimated to have cost that ,colony    
considerably over ,l#a1jjj1jjj per annum
 for several years4 ,one estimate puts  
the loss in ten years at from           
,l#ab1jjj1jjj to ,l#ae1jjj1jjj4 ,the    
hop-aphis is estimated to have cost     

,kent ,l#b1gjj1jjj in the year #ahhb4   
,in #ahgd the ,agricultural             
,commissioner of the ,united ,states    
estimated the annual loss1 due to the   
ravages of insects on cotton alone1 to  
amount to ,l#e1jjj1jjj2 and in #ahhb the
 annual loss to the ,united ,states due 
to insects1 calculated for all kinds of 
agricultural produce1 was put at the    
appalling figure of from ,l#dj1jjj1jjj  
to ,l#fj1jjj1jjj sterling4 ,in ,india1  
the annual loss due to wheat-rust alone 
has recently been estimated at          
#d1jjj1jjj to #bj1jjj1jjj rupees1 and   
one insect alone is said to have cost   
the cotton planters a quarter of the    
crop--valued at seven crores of         
rupees--in bad years4 ,similarly1 in    
,australia the annual loss from         
wheat-rust has been put at from         
,l#b1jjj1jjj to ,l#c1jjj1jjj4 ,in #ahia 
the loss in ,prussia alone from         
grain-rusts was officially estimated at 
over ,l#bj1jjj1jjj sterling4 ,need more 
be said8 ,even allowing for considerable

 exaggerations in such estimates it is  
clear that the damage to crops in any   
country soon amounts to sums which even 
at low rates of interest would easily   
yield incomes capable of supporting the 
best equipped laboratories and staffs   
for investigations directed to the      
explanation of the phenomena in detail1 
the sole basis on which intelligent     
preventive and therapeutic measures can 
be based4 ,but it is far from likely    
that the estimates are exaggerated4 ,the
 planting and agricultural communities  
are as a rule opposed to the publication
 of statistics--or at least have been so
 in various countries and at different  
times--and if we knew the damage done to
 all crops even in our own ,empire1 the 
results would probably astonish us far  
more than the above figures have done4  
,,notes ,,to ,,chapter ,,xv4       ,on  
the dissemination of fungi1 the reader  
will find ,fulton1      ,dispersal of   
the ,spores of ,fungi by the ,agency of 
,insects1      ,ann4 ,bot41 ,vol4       

,,iii41 #ahhi1 p4 #bjg1 and ,sturgis1   
,on ,some      ,aspects of ,vegetable   
,pathology and the ,conditions which    
,influence the ,dissemination of ,plant 
,diseases1 ,botanical      ,gazette1    
,vol4 ,,xxv41 #ahih1 p4 #ahg1 both      
useful papers4 ,further      information
 will be found in ,zopf1 ,die ,pilze1   
,breslau1 #ahij1      pp4 #gi-ie and    
#bbh1 and ,wagner1 ,ueber die           
,verbreitung der      ,pilze durch      
,schnecken1 in ,zeitschr4 f4 ,pflanzen  
,krankh41      #ahif1 p4 #add4 ,the     
estimates as to losses due to epidemics 
are      taken from ,watt1 ,agricultural
 ,ledger1 ,calcutta1 #ahie1 p4 #ga2     
,balfour1 ,the ,agricultural ,pests of  
,india1 ,london1 #ahhg1      pp4 #ac-ae2
 ,eriksson and ,henning1 ,die           
,getreideroste2 the      publications of
 the ,u4,s4 ,department of ,agriculture1
 ,the      ,kew ,bulletin1 and          
elsewhere4 ,the reader will find further
      examples in ,massee1 ,text-,book  
of ,plant ,diseases1 #ahii1 pp4         

#dg-ea4 ,both these subjects are well   
worth further attention1      and ,i    
know of no complete account of them4    
,,chapter ,,xvi4  ,,the ,,factors ,,of  
,,an ,,epidemic4       ,illustrations   
afforded by the potato disease--,the    
larch      disease--,the phylloxera of  
the vine4   ,when we come to enquire    
into what circumstances bring about     
those severe and apparently sudden      
attacks on our crops1 orchards1 gardens1
 and forests by hosts of some particular
 parasite1 bringing about all the       
dreaded features of an epidemic disease1
 we soon discover the existence of a    
series of complex problems of           
intertwined relationships between one   
organism and another1 and between both  
and the non-living environment1 which   
fully justify the caution already given 
against concluding that any cause of    
disease can be a single agent working   
alone4  ,the statement of prophecy that 
a particular insect or fungus need not  
be feared1 because it is found to do so 

little harm in particular cases or      
districts examined1 will thus be seen to
 be a dangerous one3 any pest may become
 epidemic if the conditions favour it6  
,in #ahdd and #ahde the potato disease  
assumed an epidemic character so        
appalling in its effects that it is no  
exaggeration to say that it constituted 
a national disaster in several          
countries4 ,it was stated at the time   
that this disease had been known for    
some time in ,belgium1 in ,canada and   
the ,united ,states1 in ,ireland1 in the
 ,isle of ,thanet1 and in other parts of
 the world4 ,similar1 but less          
devastating epidemics have occurred in  
various years since4 ,it was generally  
noticed during such epidemics that the  
plants themselves were full of foliage1 
surcharged with moisture1 and of a      
luxuriant green colour promising        
abundant crops4 ,the now well-known     
spots1 at first pale and then brown and 
fringed with a whitish mould-like       
growth--the conidiophores of the        

,phytophthora--were observed during the 
dull cloudy and wet weather1 cooler than
 usual1 when the atmosphere was         
saturated for days together1 in ,july   
and ,august4 ,the actual amount of rain 
does not appear to have been excessive1 
but most observers seem to agree that   
dull weather with moist air had         
succeeded a warm forcing period of      
growth4 ,so rapidly did the disease run 
its course that in a few days nearly all
 the plants were a rotting blackened    
mass in the fields1 and the potatoes dug
 up afterwards were either already      
rotten or soon became so in the stores4 
,further experience has confirmed this1 
and we now know that the epidemic is    
very apt to appear in any region where  
potatoes are grown on a large scale1 in 
dull moist weather1 especially in fields
 exposed to mists1 heavy dews1 etc41    
about ,july and ,august1 when the       
foliage is full and turgid4 ,similarly  
on heavy wet soils1 unless the season is
 remarkably open and dry2 but also on   

dry light soils in rainy seasons4 ,so   
evident was this that many believed that
 the mists and dew brought the          
disease--harking back to the            
superstitions of earlier days4 ,we must 
remember that prior to #ahfj the        
life-history of ,phytophthora was not   
known4 ,since ,de ,bary's proof of the  
germination of the zoospores and of the 
infection of the leaves1 the course of  
the hyphae in them and in the haulms1   
the origin of the conidia1 etc41 and the
 confirmation by numerous competent     
observers of the true fungus nature of  
this disease1 we are now in a position  
to understand the principal factors of  
the various epidemics of potato disease4
  ,it is not merely that the            
potato-fields afford plenty of food for 
the fungus1 and that the dull weather   
causes the tissues to be surcharged with
 moisture1 owing to diminished          
transpiration1 but the mists and dew--to
 say nothing of actual rain and the     
flapping of wet leaves--favour the      

germination and spread of the zoospores 
throughout the field4 ,whether the dull 
light also favours the accumulation of  
sugars in the tissues1 and the partial  
etiolation of the latter implies less   
resistance to the entering hyphae1 may  
be passed over here1 but in any case it 
is clear that we have several factors of
 the non-living environment here        
favouring the parasite and not improving
 the chances of the host1 even if they  
do not directly disfavour it4  ,as      
another instance ,i will take the       
,larch-disease1 which is due to the     
ravages of a ,peziza 7,dasyscypha       
,willkommii7 the hyphae of which obtain 
access by wounds to the sieve-tubes and 
cambium of the stem1 and gradually kill 
them over a larger and larger area and  
so ring the tree1 with the symptoms of  
canker described below4  ,now the ,larch
 fungus is also to be found on trees in 
their ,alpine home1 but there it does   
very little damage and never becomes    
epidemic except in certain sheltered    

regions near lakes and in other damp    
situations4 ,how then are we to explain 
the extensive ravages of the ,larch     
disease over the whole of ,europe during
 the latter half of this century8 ,the  
extensive planting1 providing large     
supplies for the fungus1 does not       
suffice to explain it1 because there are
 large areas of pure ,larch in the ,alps
 which do not suffer4  ,in its mountain 
home the ,larch loses its leaves in     
,september and remains quiescent through
 the intensely cold winter1 until ,may4 
,then come the short spring and rapid   
passage to summer1 and the ,larch buds  
open with remarkable celerity when they 
do begin--i4e4 when the roots are       
thoroughly awakened to activity4 ,hence 
the tender period of young foliage is   
reduced to a minimum1 and any agencies  
which can only injure the young leaves  
and shoots in the tender stage must do  
their work in a few days1 or the        
opportunity is gone1 and the tree passes
 forthwith into its summer state4  ,in  

the plains1 on the contrary1 the ,larch 
begins to open at varying dates from    
,march to ,may1 and during the tardy    
spring encounters all kinds of          
vicissitudes in the way of frosts and   
cold winds following on warm days which 
have started the root-action--for we    
must bear in mind that the roots are    
more easily awakened after our warmer   
winters than is safe for the tree4  ,it 
amounts to this1 therefore1 that in the 
plains the long continued period of     
foliation allows insects1 frost1 winds1 
etc41 some six weeks or two months in   
which to injure the slowly sprouting    
tender shoots1 whereas in the mountain  
heights they have only a fortnight or so
 in which to do such damage4 ,that the  
lower altitude and longer summer are not
 in themselves inimical to ,larch is    
proved by the splendid growths made by  
the trees first planted a century ago4  
,then came the epidemic of              
,larch-disease3 the fungus1 which is    
merely endemic--i4e4 obtains a          

livelihood here and there on odd trees1 
or groups of trees in warmer or damper  
nooks--in the ,alps1 was favoured by the
 more numerous points of attack afforded
 to its spores by injuries due to       
insects--,coleophora1 ,chermes1         
etc4--and frost wounds1 as well as by   
the longer periods of moist dull        
weather1 and the longer season of       
foliation4 ,moreover1 as time went on   
almost every consignment of young       
,larch-trees sent abroad was already    
infected4 ,here again1 then1 we find the
 factors of an epidemic consisting in   
events which favour the reproduction and
 spread of a fungus more than they do   
the well-being of the host4  ,as a third
 illustration ,i will take the case of  
an insect epidemic4 ,in #ahfc a disease 
was observed on vines in the ,south of  
,france which frightened the growers as 
they realised its destructive effects3  
the roots decayed and the leaves turned 
yellow and died before the grapes       
ripened1 and such vines threw out fewer 

and feebler shoots the following year1  
and often none at all afterwards4 ,in   
#ahfe the disease was evidently becoming
 epidemic near ,bordeaux1 and in #ahfh  
it was shown to be due to an insect1    
,phylloxera1 the female of which lays   
its eggs on the roots1 where they hatch4
 ,the louse-like offspring sticks its   
proboscis into the tissues as far as the
 central cylinder4 ,the irritated       
pericycle and cortex then grow and form 
nodules of soft juicy root-tissue at    
which the insect continues to suck4     
,rapid reproduction results in the      
majority of the young rootlets being    
thus attacked1 and since they cannot    
form their normal periderm and harden   
off properly they rot1 and admit fungi  
and other evils1 in consequence of which
 the vine suffers also in the parts     
above ground4  ,evidence that the       
general damage is due to the diminished 
root-action is found in the peculiarly  
dry poor wood formed in the canes of    
diseased plants4  ,by #ahgg the epidemic

 had spread to the northern limits of   
the ,french vineyards1 and by #ahhh half
 the vines in the country were attacked1
 and the yield of wine reduced from half
 a million hectolitres to #ej1jjj only4 
,meanwhile the disease had spread to    
,italy1 ,germany1 ,madeira1 ,portugal1  
and even to the ,cape1 though not in    
epidemic form as in the ,bordeaux centre
 whence it spread4  ,now it appears that
 ,phylloxera has long been in the habit 
of doing damage to vines in ,america1   
where1 however1 it attacks the leaves1  
on which it makes pocket-like galls1    
rather than the roots4 ,moreover1 there 
are species and varieties of ,american  
vines which1 even when planted in       
,europe1 do not suffer at all from this 
insect at the roots1 either because the 
rootlets do not push out at the same    
season as those of the ,european form1  
or because they form wood more rapidly  
and completely1 or secrete resinous and 
other matters distasteful to the insect 
in greater quantity and are thus capable

 of healing the wounds1 or in some other
 way they do not respond to the attack  
or suit the insect4 ,in any case the    
attack on the leaf rather than the root 
seems to be the exception in ,european  
vineyards and the rule in ,american     
species1 and we appear to be face to    
face with a problem of specific         
predisposition to this particular       
malady4 ,that the resistant properties  
of the vines of ,america--not all1 only 
particular species and varieties are    
thus immune--can be utilised has been   
proved by ,european growers2 and not    
only so1 for ,millardet and others have 
shown that the ,european vine grafted on
 to these resistant stocks suffer less  
than when on their own roots4 ,it has   
also been shown that hybrids can be     
obtained which are resistant4  ,but the 
most curious point of all is that       
,phylloxera was itself a native of      
,america1 and came thence to ,europe4   
,it had played its part with certain    
fungi in ruining all the attempts to    

introduce the ,european vine into       
,america many years ago4 ,a recent      
authority on the evolution of ,american 
fruits writes as follows3  ,all the most
 amenable types of grapes had long since
 perished in the struggle for existence1
 and the types which now persist are    
necessarily those which are1 from their 
very make-up or constitution1 almost    
immune from injury1 or are least liable 
to attack 4 4 4 the ,phylloxera finds   
tough rations on the hard1 cord-like    
roots of any of our eastern species of  
grapes4 ,but an unnaturalised and       
unsophisticated foreigner1 being unused 
to the enemy and undefended1 falls a    
ready victim2 or if the enemy is        
transported to a foreign country the    
same thing occurs4  ,further proof that 
it is in the constitution of the        
,european vine that the want of         
resistance to ,phylloxera resides1 is   
furnished by the fact that in           
,california and the ,pacific states the 
,european vine was introduced with more 

success1 but is now suffering badly     
because ,phylloxera has spread there    
also4 ,it must not be overlooked1       
however1 that we are as yet very        
ignorant of all that is implied in the  
word constitution as used above4  ,if we
 enquire further why the ,phylloxera    
epidemic was so much worse in the       
,southern vineyards than in the more    
,northern ones of ,germany1 the opinion 
seems to prevail that the warmer        
climates favour the insect4 ,further1 it
 appears that1 in ,italy1 the vines in  
loose open soil1 provided it is equally 
rich in mineral food-materials and      
offers no disadvantages as regards      
drainage1 suffer less than those in     
closer soils1 the reasons alleged being 
that the young roots can push out more  
rapidly and widely1 and so obtain       
holdfasts with greater distances between
 them4   ,,notes ,,to ,,chapter ,,xvi4  
,the student may obtain further         
information on the history of      the  
,potato disease by consulting the       

following3 ,berkeley1                   
,observations1 ,botanical and           
,physiological1 on the ,potato          
,murrain1 ,journal of the ,horticultural
 ,society1 ,vol4 ,i41      #ahdf1 p4 #i2
 ,de ,bary1 ,die ,gegenwaertig          
herrschende ,kartoffel      ,krankheit1 
etc41 ,leipzic1 #ahfa2 and the pages of 
the      ,gardeners' ,chronicle from    
#ahfj-aijj4       ,for the ,larch       
disease he should consult ,hartig1      
,unters4 aus      der ,foist4           
,botanischen ,inst4 ,muenchen1 ,b4 ,i41 
#ahhj2 and      ,willkomm1 ,microscop4  
,feinde des ,waldes1 ,b4 ,,ii41 #ahfh4  
,for ,phylloxera the literature is      
chiefly in the ,comptes      ,rendus and
 other ,french publications since #ahge1
 and in the      ,reports of the ,u4,s4 
,dept4 of ,agriculture4       ,for a    
summary of the facts concerning the     
life-histories of      the parasites    
referred to above1 see ,frank1          
,krankheiten der      ,pflanzen1 and    
,marshall ,ward1 ,diseases of ,plants1  

p4 #ei1 and      ,timber and ,some of   
its ,diseases1 ,london1 #ahhi1 chapter  
,x4       ,also ,marshall ,ward1 ,on    
some ,relations between ,host and       
,parasite in certain epidemic ,diseases 
of ,plants1 ,proc4 ,roy4      ,soc41    
,vol4 ,,xlvii41 #ahij1 pp4 #cic-ddc2 and
 ,illustrations of      the ,structure  
and ,life-history of ,phytophthora      
infestans1      ,quart4 ,journ4         
,microsc4 ,soc41 ,vol4 ,,xxvii41 #ahhg1 
p4 #dac2 also      ,marshall ,ward1     
,researches on the ,life-history of     
,hemileia      vastratrix1 ,journ4      
,linn4 ,soc41 ,vol4 ,,xix41 #ahhb1 p4   
#bii2 and      ,on the ,morphology of   
,hemileia vastatrix1 ,quart4 ,journ4    
,microsc4 ,soc41 #ahha1 ,vol4 ,,xxi41 p4
 #a4     ,,chapter ,,xvii4  ,,remedial  
,,measures4       ,preventible          
diseases--,the principles of            
therapeutics--,powders      and their   
application--,spraying with             
liquids--,nature of      chemicals      
employed--,employment of epidemics and  

natural      checks--,the struggle for  
existence4   ,it may be said that in no 
connection is the proverb ,prevention is
 better than cure more applicable than  
with this subject1 and undoubtedly the  
best utilitarian argument that can be   
used in favour of a thorough study of   
the causes of disease is that only by   
understanding these causes is there any 
hope of avoiding the exposure of crops1 
garden plants1 forest trees1 etc41 to   
the attacks of preventible diseases4    
,moreover1 only an intelligent          
appreciation of the causes of a disease 
will enable the cultivator to take steps
 to mitigate their effects when once the
 damage has begun its course4 ,every    
cultivator learns by experience or by   
precept that there are some things he   
must avoid in dealing with certain      
plants1 or otherwise they will not      
succeed2 in other words they will       
succumb to diseased conditions and die4 
,it is partly owing to the want of      
systematisation of this knowledge1 and  

its extension in other directions1 that 
such extraordinary blunders are made in 
ignorant practice1 and trees for        
instance are planted in low-lying frost 
beds which would succeed in slightly    
higher situations1 or seeds subject to  
damping-off are sown in beds rife with  
the spores of ,peronospora or ,pythium1 
and so forth4  ,many diseases1 however1 
are not preventible in the present state
 of our knowledge1 or prevailing        
conditions are such that the risk must  
be run of endemic diseases gradually    
becoming epidemic1 and thus the natural 
desire for some means of checking the   
ravages of some pest or another has led 
to innumerable trials to minimise the   
effects by prophylactic measures4 ,the  
procedure almost invariably followed    
where parasites are concerned1 consists 
in either dusting the plants with some  
chemical in the form of a powder1 or    
spraying it with a liquid1 or           
occasionally in enveloping the plant in 
some gas1 in each case poisonous to the 

insect- or fungus-pest4 ,the principal  
rules to be observed are3 7#a7 the      
poison employed must be sufficiently    
strong or concentrated to kill the      
parasite1 but not sufficiently powerful 
to injure the host2 7#b7 it must be     
applied at the right period1 as         
suggested by a knowledge of the         
life-history of the fungus or insect in 
question4  ,obviously it is of no use to
 apply such topical remedies to a       
parasite while it is spending the       
greater part of its life inside the     
tissues of the host4 ,further1 questions
 of expense of the materials employed   
and of the labour of applying them help 
to limit the adoption of such measures4 
,among the various kinds of powders     
employed1 finely divided sulphur1 or a  
mixture of sulphur and lime1 have been  
used with success in some cases--e4g4   
against ,hop mildew and other epiphytic 
,erysipheae1 and against red spider1    
aphides1 etc41 the gaseous sulphur      
dioxide evolved being the efficacious   

agent4 ,in other cases pyrethrum or     
tobacco powder1 wood ashes1 etc41 have  
been employed against insects4 ,such    
powders are applied by hand or by means 
of bellows1 and are very easily         
manipulated in most cases1 though1 like 
all such applications1 the dangers of   
concentration at particular spots owing 
to uneven distribution1 or of dilution  
and washing off by rain1 have to be     
incurred4  ,far more numerous are the   
various liquids which have been employed
 for washing1 spraying1 or steeping the 
affected parts of diseased plants4      
,water alone1 or aqueous decoctions or  
emulsions of various kinds--e4g41       
quassia1 tobacco1 soap1 or aloes1 have  
been widely employed against insects    
such as green fly1 red spider1 etc4 ,in 
greenhouses1 where the leaves can be    
washed by hand or thoroughly syringed1  
and the concentration and time of action
 thoroughly controlled1 such liquids are
 often serviceable1 but great practical 
difficulties are apt to interfere with  

their use in the open field4  ,the      
principal liquids employed against fungi
 have been copper sulphate and other    
metallic compounds 7,bordeaux mixture1  
,eau ,celeste1 etc471 various compounds 
of arsenic 7e4g4 ,paris green71         
potassium sulphite1 permanganate1 etc41 
and emulsions of carbolic acid1         
petroleum1 and such like antiseptics1   
for the exact composition of which the  
special treatises must be consulted4    
,some of these1 especially ,bordeaux    
mixture1 have been experimented with on 
a very large scale1 especially in       
,america1 and various forms of spraying 
machines have been introduced for       
dealing with large areas4  ,it is clear 
that these spraying operations are more 
particularly adapted to field crops such
 as ,turnips1 ,hops1 ,vines1 ,potatoes1 
and to garden and greenhouse plants than
 to woods and plantations2 as a rule    
they cannot be applied to forest        
trees--though they have been used in    
orchards--or to roots1 seeds1 and other 

parts in the soil1 and many special     
forms of treatment have been devised for
 particular cases of these kinds4  ,one 
of the oldest of these is the steeping  
of grain in solutions of copper1 or in  
hot water1 just before sowing1 and the  
practical eradication of ,bunt and1     
partially1 of ,smut is due to this      
practice1 which has lately been adapted 
to potatoes1 the principle being that   
the parasitic germs shall be killed     
while still adhering to the outside of  
the seeds1 tubers1 etc41 before         
germination4 ,finger and ,toe due to    
,plasmodiophora has been successfully   
dealt with by the application of lime1  
but we do not know whether the effect is
 owing to indirect actions in the soil1 
to direct actions on the plasmodia1 or  
to the increased production of          
root-hairs induced by liming4           
,phylloxera has been treated by plunging
 into the soil near the roots small     
blocks of some slowly-soluble medium1   
such as gelatine1 impregnated with      

carbon-bisulphide1 the volatile fumes of
 which kill the insect1 and even more   
drastic remedies have been tried along  
similar lines4 ,in ,america orchard     
trees infested with insects or fungi    
have been covered one by one with light 
tents1 and the vapours of prussic acid1 
burning sulphur1 and other poisons      
allowed to act inside the tent4 ,in all 
such cases it must be remembered that   
uncontrolled ignorance of the properties
 of poisons on the part of the operator 
may lead to disaster1 and the same      
applies to the much easier treatment of 
greenhouses1 and cases where poisoned   
food is laid about for insects or       
vermin4  ,attempts1 not altogether      
unsuccessful on the small scale1 have   
also been made to introduce epidemic    
diseases among rats1 mice1 and locusts  
and other insects1 by inoculating some  
of them with parasitic bacteria or fungi
 7,empusa1 ,isaria1 etc471 and then     
allowing them to run loose in the hope  
that they will communicate the disease  

to their fellows4 ,the introduction of  
lady-birds into districts infested with 
,coccideae and similar pests which they 
devour1 is also recorded as successful1 
as also the importation of birds into   
forests plagued with caterpillars4 ,it  
must not be over-looked1 however1 that  
man's interference with the existing    
balance of events in the natural        
struggle for existence is occasionally  
disastrous1 as witness the results of   
importing rabbits into ,australia1 goats
 into the ,canary ,islands1 and sparrows
 in various countries4 ,darwin's        
well-known illustration of the          
inter-relations between clover1 bees1   
field-mice1 and cats 7,orig4 of         
,species1 #fth ed41 #ahgf1 p4 #eg71     
which shows the astounding probability  
of the dependence of such a plant on the
 number of cats in the neighbourhood1   
well illustrates the situation4  ,mere  
mention must be made of other special   
treatments4  ,caterpillars and larger   
animals are often picked by hand or     

their natural enemies--e4g4 birds1 are  
encouraged in forests4 ,locusts are     
caught in nets1 trenches1 etc41 and     
buried4 ,woodlice1 slugs1 etc41 are     
often trapped by laying attractive food 
such as carrots and overhauling the     
traps daily3 similarly with earwigs4    
,rings of tar round tree stems have been
 employed to prevent caterpillars       
creeping up them4  ,american ,blight has
 been treated by rapidly flaming the    
stems4 ,syringing with hot water has    
also been employed for vines affected   
with mildew1 mealy bug1 etc4  ,with     
regard to the alleged immunity from     
devouring insects of certain poisonous  
plants1 it has been pointed out that    
,pangium edule1 which abounds in prussic
 acid1 is infested with a grub1 and ivy 
is occasionally eaten by caterpillars4  
,another point as regards insect pests  
is the well-known destructive effect of 
a cold1 wet spring on the young larvae4 
,the use of cyanide of potassium        
requires especial care1 but has been    

described as easily carried out with    
success in greenhouses4  ,it seems      
probable that lady-birds1 the larvae of 
wasp-flies and lace-wings1 and          
ichneumon-flies as well as wrens can    
keep down aphides4  ,for an example of  
the treatment of a complex case of      
chlorosis with mineral manures1 the     
reader may consult the ,gardeners'      
,chronicle1 #ahii 7,july71 p4 #dje4     
,many similar cases have been recorded1 
but it should not be overlooked that    
very complex inter-relations are here   
involved4  ,charlock has been           
successfully dealt with by applying #e  
lbs4 of copper sulphate in #be gallons  
of water to each acre of land while the 
weeds are young4  ,in all these cases   
the guiding idea is derived from        
accurate knowledge of the habits of the 
insect1 fungus1 or pest concerned1 and  
obviously the procedure must be timed   
accordingly4 ,it is a particular case of
 the struggle for existence1 where man  
steps in as a third and 7so to speak7   

unexpected living agent4  ,it is clear  
from our study of the factors of an     
epidemic that one of the primary        
conditions which favour the spread of   
any disease is provided by growing any  
crop continuously in pure culture over  
large areas4 ,this is sufficiently      
exemplified by the disastrous spread of 
such diseases as ,wheat-rust1           
,larch-disease1 ,potato-disease1        
,phylloxera1 ,hop-disease1 ,sugar-cane  
disease1 ,coffee-leaf disease1 and      
numerous other maladies which have now  
become historic in agricultural1        
planting1 and forest annals4 ,providing 
the favourite food-supply in large      
quantities is not the only factor of an 
epidemic1 but it is a most important one
 in that it not only facilitates the    
growth and reproduction of a pest1 but  
affords it every opportunity of         
spreading rapidly and widely4           
,moreover1 ,nature herself shows us that
 such pests are kept in check in her    
domain by the struggle for existence    

entailed by innumerable barriers and    
competitors4 ,as matter of experience   
also it is found that rotation of crops1
 planting forests of mixed species1 and 
breaking up large areas of cultivation  
into plantations1 fields1 etc41 of      
different species afford natural and    
often efficient checks to the ravages of
 fungus and insect pests4 ,over and over
 again it has been found that a fungus  
or an insect which is merely endemic so 
long as it is isolated in the forest1   
where its host is separated from other  
plants of the same species by other     
plants which it cannot attack1 becomes  
epidemic when let loose on the          
continuous acres so beloved of the      
planter4 ,and the same reasoning applies
 to the success of such pests on open   
areas from which the birds or other     
enemies of the pest have been driven4   
,true1 we cannot always trace the       
tangled skein of inter-relationships    
between one organism and another in     
,nature3 the recognition of the         

principle of natural selection and the  
struggle for existence is too recent1   
and our studies of natural history as   
yet too imperfect to lay all the factors
 clear1 but no observant and thoughtful 
man can avoid the truth of the general  
principle here laid down4 ,the history  
of all great planting enterprises       
teaches us that he who undertakes to    
cultivate any plant continuously in open
 culture over large areas must run the  
risk of epidemics4   ,,notes ,,to       
,,chapter ,,xvii4       ,the principal  
literature1 now very voluminous1 on this
 subject      is contained in the       
publications of the ,u4,s4 ,department  
of      ,agriculture from #ahij onwards4
 ,see especially ,bulletins1      ,nos4 
#c1 #f1 and #i2 ,farmers' ,bulletin1    
,no4 #ia1 #ahii2 and ,the      ,journal 
of ,mycology during the same period4    
,see also ,lodeman1      ,the ,spraying 
of ,plants1 ,london1 #ahif4 ,a summary  
of the      principal processes will be 
found in ,massee1 ,text-,book of        

,plant ,diseases1 pp4 #ca-dg4           
,with regard to the history of the      
subject1 which still needs      writing1
 the reader should not overlook         
,roberts1 ,on the      ,therapeutical   
,action of ,sulphur1 ,st4 ,george's     
,hospital      ,reports1 date unknown1  
but subsequent to the following3        
,berkeley1 ,introduction to ,cryptogamic
 ,botany1 #aheg1 p4 #bgg1      with     
references4 ,these are1 ,i believe1 with
 the references to      steeping of     
wheat in ,de ,bary1 ,unters4 ueber d4   
,brandpilze1      ,berlin1 #ahec1 among 
the first attempts to utilise such      
remedies4       ,further facts will be  
found in the pages of the ,gardeners'   
,chronicle1 especially since #ahij1 and 
in ,zeitsch4 f4                         
,pflanzen-krankheiten since #ahia4      
,,chapter ,,xviii4  ,,variation ,,and   
,,disease4       ,predisposition and    
immunity--,pathological conditions      
vary--,hardy varieties--,disease-proof  
varieties--,disease      dodging--,thick

 skins--,indian wheats1 etc4            
,cell-contents      vary--,citrus1      
,cinchona1 ,almonds1 etc4 ,double ideals
 in      selection--,cultivation of pest
 and host-plant--,variations of         
fungi--,bacteria--,specialised          
races--,difficulties--,experiment       
only will solve the problems4   ,the    
numerous and often expensive failures in
 the application of any prophylactic    
treatment1 have proved an acute stimulus
 to the research for other ways of      
combating the ravages of plant diseases4
 ,it is a matter of every-day experience
 that particular varieties of cultivated
 plants may suffer less from a given    
disease than others in the same         
district2 also that one and the same    
species may suffer badly in one country 
and not in another--e4g4 the ,larch in  
the lowlands of ,europe as contrasted   
with the same tree in its ,alpine home1 
and the various species of ,american    
,vines in ,europe4  ,these matters1 in  
the hands of astute observers1 are      

turning the attention of cultivators and
 experts to new aspects of the question 
of plant diseases1 namely1 the possible 
existence of immunity1 and the breeding 
of disease-proof varieties2 and the     
existence on the part of the host plant 
of predispositions to disease which may 
depend on some factors in the plant or  
in the environment over which it is     
possible to exercise control1 or which1 
if known1 can be avoided4  ,the matter  
is complicated by the recent            
demonstration of the fact that parasites
 also vary and can adapt themselves to  
altered conditions1 as is shown by the  
history of the coffee-leaf disease      
7,hemileia7 in ,ceylon1 and by          
,eriksson's results with ,wheat-rusts   
7,puccinia7 and various experiments with
 ,coleosporium and other ,uredineae2 but
 there are good grounds for concluding  
that hybridisation1 grafting1 and       
selection of varieties may do much      
towards the establishment of races which
 will resist particular diseases1 as    

shown by ,millardet's experiments with  
,vines1 and the results obtained by     
,cobb and others with ,wheat4  ,the     
great difficulty with so-called         
disease-proof varieties is to test them 
under similar conditions in different   
countries1 and for a sufficient period  
of time4 ,a particular race of ,wheat   
may behave very differently in ,norfolk1
 ,devonshire1 and ,northumberland1 and  
the recent introduction of the purely   
experimental method in this connection  
is a marked advance4 ,however rough the 
experiments may of necessity have to be1
 it is only by such means that data can 
be gradually accumulated4  ,having now  
obtained some insight into the factors  
concerned in disease1 let us enquire    
further into the bearing of variation on
 these4 ,it is evident that pathological
 conditions may vary2 indeed they are   
themselves symptoms of variation1 as we 
have seen4 ,the history of all our      
cultivated plants shows abundantly that 
many of the variations obtained by      

breeding in our gardens1 orchards1      
fields1 etc41 involve differences of    
response on the part of the plant to the
 very agencies which induce disease4    
,every year the florists' catalogues    
offer new hardy varieties2 but a hardy  
variety is simply1 for our present      
purpose1 one which succumbs less readily
 to frost1 cutting winds1 cold damp     
weather1 and so forth4 ,if anyone doubts
 that hardy varieties have been         
gradually bred by selection1 ,i refer   
him to the evidence collected by ,de    
,candolle1 ,darwin1 ,wallace1 ,bailey   
and others4 ,when we come to enquire    
into the causes of hardiness1 however1  
difficulties at once beset us4 ,the     
adaptation may express itself in a      
difference in the time of flowering or  
leafing1 the exigencies of the season   
being dodged1 as it were1 in a manner   
which was impossible with the original  
stock1 as appears to have occurred with 
,peaches in ,america2 or it may be      
expressed in deeper rooting1 as is said 

to be the case in some ,apples1 or in   
the acquirement of a more deciduous     
habit1 or in actually increased         
resistance to low temperatures4 ,in such
 cases we cannot trace what alterations 
have occurred in the cells and tissues  
concerned1 though we may be sure that   
some changes do occur4  ,no experienced 
cultivator doubts that some varieties of
 ,potato1 ,wheat1 ,vine1 ,chrysanthemum1
 etc41 suffer more from epidemic        
diseases than others1 and our yearly    
catalogues furnish us with plenty of    
promises of disease-proof varieties4    
,here also we may imagine several ways  
in which a particular variety may resist
 or escape the epidemic attacks of fungi
 which in the same neighbourhood        
decimate other varieties4 ,if we could  
breed a variety of the ,larch which     
opened its buds later than the ordinary 
form in our northern plains1 the        
probability of its escaping the         
,larch-disease would be increased in    
proportion to the shortness of the      

period of tender foliation described on 
p4 #aec4 ,it has been claimed for       
certain varieties of ,wheat that        
increased thickness of the cuticle and  
fewer stomata per square unit of surface
 have diminished the risk of infection  
by ,rust fungi1 and for certain         
varieties of ,potato1 that the thicker  
periderm of the tuber protects them     
against fungi in the soil4 ,that certain
 thick-skinned ,apples1 ,tomatoes1 and  
,plums pack and store better than those 
with a more tender epidermis seems      
proved--that is to say1 they suffer less
 from fungi which gain access through   
bruises and other wounds2 but it cannot 
be said that any convincing proof is yet
 to hand explaining in detail why some  
races of wheat resist ,rust1 or why the 
roots of ,american ,vines suffer less   
from ,phylloxera than others4  ,one of  
the most extraordinary cases known to me
 in this connection is the unconscious  
selection on the part of native ,indian 
cultivators1 perfectly ignorant of the  

principles involved1 of spring and      
autumn forms of ,rice1 ,wheat1 ,castor  
,oil1 ,sugar ,cane1 ,cotton1 and other  
crops4 ,it has been estimated that      
,bengal alone possesses as many as      
#aj1jjj recognisable forms of rice4 ,now
 there is not the slightest ground for  
doubt that these have been unconsciously
 bred from the semi-aquatic native      
species during the many centuries of    
,indian agriculture1 and nevertheless   
they have1 among other peculiar races1  
some hill-breeds which they cultivate on
 dry soils and without direct           
inundation4 ,that is to say1 they       
possess tropical and temperate races    
differing far more than our spring and  
summer wheats4  ,something has been     
gained1 then1 if we can show that there 
is nothing absurd or hopeless in the    
search for disease-proof or resistant   
races1 and ,i think this can be done4   
,we must not forget that the ideal      
usually set before himself by a breeder 
of plants has hitherto been almost      

exclusively some standard of size1 form1
 colouring1 and so forth1 of the flower1
 or of taste and texture of the fruit1  
tuber1 etc41 though experiments with    
,cinchona1 with brewery yeasts1 and     
other plants remind us that variations  
in other directions have been attended  
to also4  ,now it is obvious that in    
breeding sour limes and sweet oranges   
the cultivator is selecting1 and        
intensifying by selection1 very         
different metabolic processes in the    
cell3 he can test the results of these1 
and so the selection proceeds4  ,the    
question is1 ,could he select at the    
same time those variations in cell      
activity which express themselves in    
properties of the flower1 fruit1        
foliage1 etc41 he desires1 as well as   
such variations as aid the cells in     
repelling fungi1 insects1 or exigencies 
of the non-living environment8  ,that   
more or less disease-proof varieties    
could be selected if that object alone  
were kept in view can hardly be doubted2

 plenty of examples exist already which 
show that the necessary variations to   
work upon exist in just those secretions
 of protoplasm1 etc41 which we have seen
 are concerned in repelling or          
attracting parasites4  ,the ,sweet      
,almond has lost the power of producing 
amygdalin and prussic acid in its cells2
 ,cinchona plants vary immensely in the 
quantity of quinine formed1 and in      
,european hot-houses may even form none 
at all2 some varieties of ,maize have   
sugar and dextrine instead of starch in 
their endosperms1 or coloured instead of
 clear sap in the aleurone layer1 and   
recent researches prove that they can   
transmit these peculiarities to hybrid  
offspring2 non-poisonous bacteria have  
frequently been got from poisonous      
species simply by cultivation under     
special conditions1 and pigmented forms 
can be bred into non-pigmented races4   
,but we see that the difficulty of      
selection is increased in the case      
postulated above1 because two ideals are

 to be worked up to1 and they may       
conceivably be incompatible4 ,not       
necessarily so1 however1 for breeders   
have solved such problems before in     
obtaining early and heavy cropping races
 of potatoes1 wheat1 etc41 sweet and    
large grapes1 strawberries1 etc41 hardy 
and brilliant flowers1 and so forth4    
,there is1 however1 another aspect of   
this question of variability in         
organisms in this connection to be      
considered4 ,ever since cultivation     
began man has probably been cultivating 
not only the crops he desires1 but also 
the pests which infest them1 and if     
variation of his chosen plants          
occurs--and no one will deny            
that--surely variation of the fungi and 
insects which live on them also takes   
place4 ,that this is so can be          
demonstrated1 though1 since it is not   
part of my theme to go into the question
 of peculiarities of species and races  
of parasites1 the subject must here be  
passed over with a few remarks only4    

,recent researches have shown not only  
that fungi vary immensely in form and   
morphological characters according to   
the amount and kind of food-materials   
put at their disposal1 thus bringing the
 whole question of polymorphism into the
 domain of experimental physiology1 but 
that their capacities for infection1    
spore formation1 etc41 are also capable 
of variation and are dependent on the   
quality and quantity of food supplies1  
water1 as well as on the temperature1   
illumination1 and other factors of the  
environment4 ,this is true of parasites 
as well as of saprophytes4 ,botrytis    
forms conidia only in darkness and in   
moist air4 ,klebahn found that a        
,puccinia growing on ,digraphis infected
 ,polygonatum readily and completely1   
,convallaria imperfectly1 whereas if    
sown on ,majanthemum it only just       
infected the plant and then remained    
sterile1 while it refused to infect     
,paris at all4 ,magnus has shown that   
,peronospora parasitica can only infect 

meristematic tissues1 and that when it  
co-exists with ,cystopus on ,capsella1  
as is usually the case1 it enters the   
latter plant by infecting the gall-like 
pustules of hypertrophied tissue induced
 by that parasite4 ,numerous parasitic  
fungi can only penetrate particular     
parts of plants4 ,for instance1 the     
,ustilago of wheat can only infect the  
young seedling1 and grows for weeks as a
 barren mycelium1 only becoming a       
dominant fungus in the endosperm4       
,numerous other examples could be given1
 but these suffice to show some of the  
ways in which the nature of the food    
substratum supplied by the host affects 
the fungus4 ,it is obvious that if the  
nature of this food changes1 the fungus 
is also affected1 and no doubt this is  
the principal reason why ,rust-fungi1   
for instance1 vary so much in their     
vigour and reproductive power on        
different wheats and grasses1 though the
 other factors of the environment must  
also be of influence on them as well as 

on the hosts4  ,but--and this is the    
second point--modern research is also   
showing that the various species of     
,rust-fungi have split up into different
 varieties or specialised races1        
according to the particular host plants 
they inhabit4 ,for instance there are   
special varieties or races of the       
particular species known as ,puccinia   
graminis1 the wheat rust1 each of which 
grows well on various kinds of grain and
 grasses but refuses to infect others4  
,thus1 the variety which infects ,wheat 
refuses to infect ,barley or ,oats1     
while that variety which grows on ,rye  
will not take on ,wheat and so forth4   
,now it is important to notice that     
these specialised races are             
indistinguishable one from another by   
their visible microscopic characters3   
they are all botanically of the species 
,puccinia graminis which forms its      
aecida on the ,barberry4 ,we must       
therefore conclude that we have here the
 same phenomenon as that met with in    

culture-races of bacteria which1 having 
been fed for several generations on     
media rich in proteids1 refuse to grow  
on media rich in carbohydrates1 or when 
attenuated races are developed by       
culture under special conditions4  ,now 
since such physiological races as ,i    
have described are by no means confined 
to ,puccinia but are also known in      
,melampsora1 ,gymnosporangium and other 
fungi1 we must conclude from this and   
from what we know of variation in plants
 and animals generally1 that variation  
and adaptation are common among         
parasites1 insects as well as fungi4    
,these considerations will serve to show
 moreover that the question of breeding 
disease-proof varieties of our          
cultivated plants is complicated by the 
danger of our breeding at the same time 
adapted races of their pests4 ,it       
appears at first sight extremely        
improbable that we should escape the    
danger by breeding from those specimens 
of our plants which have best survived a

 fungus epidemic4 ,still1 it must not be
 forgotten that hardy varieties1 and    
races adapted to other exigencies of the
 non-living environment1 have been bred 
by selection--and nevertheless this     
variable non-living environment is      
always with us4 ,the matter is therefore
 simply and solely one of experiment1   
and the retort that a disease-resisting 
variety of any particular plant has not 
yet been raised is no more valid than   
the objection that a true blue primrose 
has not yet been obtained3 whether the  
same remark can be made with regard to  
any hope of a disease-proof plant may be
 another matter1 but in any case it must
 be made more cautiously in the light of
 our present experience4   ,,notes ,,to 
,,chapter ,,xviii4       ,the reader    
will find more on this subject in       
,bailey's      ,survival of the ,unlike 
and the literature quoted in the        
notes to ,chapter ,,viii4       ,for    
varieties of ,indian ,wheats1 etc41 see 
,watt1 ,agricultural      ,ledger1      

,calcutta1 #ahie4       ,for a          
discussion on so-called ,disease-proof  
,wheats consult      ,eriksson          
,henning1 ,die ,getreideroste4          
,magnus' paper is in the ,berichte der  
,deutschen bot4      ,gesellsch41 #ahid1
 p4 #ci4       ,concerning physiological
 races and adapted varieties of         
,puccinia1 etc41 see ,eriksson1 ,a      
,general ,view of the      ,principal   
,results of ,swedish ,research into     
,grain ,rust1      ,botanical ,gazette1 
vol4 #be1 #ahih1 p4 #bf4       ,for an  
account of ,wheat-rust see ,marshall    
,ward1 ,illustrations      of the       
,structure and ,life-history of         
,puccinia graminis1      etc41 ,ann4 of 
,bot41 #ahhh1 ,vol4 ,,ii41 p4 #bae4     
,,chapter ,,xix4  ,,symptoms ,,of       
,,disease4                              
,discolorations--,pallor--,etiolation--,
laying of ,wheat--                      
,chlorosis--,yellowing--,albinism--,vari
egation--,uprooting1      ,exposure and 
,wilting of seedlings4   ,everybody     

knows in a general way when the         
geraniums in the window pots are        
drooping from want of water1 or when the
 young ,wheat is sickly1 or the         
,pear-trees blighted1 and we have now to
 see how far we can systematise the     
knowledge that has been gained in course
 of time regarding the signs which sick 
plants exhibit4  ,pallor4--,under this  
heading1 which includes all cases where 
the normal healthy green colour is      
replaced by a general sickly yellow or  
pale hue1 ultimately resulting in death 
of the parts if not arrested1 we have   
several totally distinct diseases of the
 chlorophyll apparatus1 each recognised 
by the co-existence of other subordinate
 symptoms4 ,the principal varieties of  
pallor usually met with are the         
following3  ,etiolation is due to       
insufficient intensity of light1 the    
pale sickly yellow organs being         
unusually watery and deficient in       
vascular tissue1 the internodes         
abnormally long and thin1 and the leaves

 generally reduced in size1 or1 in some 
plants also drawn4  ,forced ,endive1    
,rhubarb1 ,asparagus1 and earthed       
,celery afford examples of etiolation   
purposely induced4 ,the want of light   
causes the true chlorophyll colouring   
matter to remain in abeyance1 and       
consequently the plant as a whole       
suffers from carbohydrate starvation4   
,laying of ,wheat and other cereals is a
 particular case of etiolation4 ,the    
seeds having been sown too thickly1 the 
bases of the haulms1 owing to the       
etiolation and consequent lack of       
carbohydrates1 suffer from want of      
stiffening tissues1 and the top-heavy   
plants fall over4  ,false etiolation    
depends on a similar abeyance of the    
chlorophyll1 but in this case due to too
 low a temperature4 ,it is often seen in
 ,wheat and other monocotyledons when   
the young leaves unfold in cold weather 
in spring4 ,the symptoms of drawing and 
tenderness are however absent4  ,pallor 
due to too intense illumination must be 

kept sharply distinct from etiolation1  
the pale green or yellow hue being here 
due to the destruction of the           
chlorophyll by insolation1 and the      
accessory symptoms of drawing are       
wanting4  ,chlorosis is a form of pallor
 where the chlorophyll grains themselves
 are fully developed1 but their green   
pigment remains in abeyance owing to a  
deficiency of iron in the soil1 and can 
often be cured by adding traces of a    
ferrous salt4 ,the distinction between  
,icterus1 where the organs are only     
yellow1 and ,chlorosis proper1 where    
they are nearly white cannot always be  
maintained4 ,in the typical case only   
those organs whose cells are still young
 can become green on adding iron4       
,yellowing or ,false ,chlorosis may be  
experimentally induced by too much      
carbon-dioxide in the atmosphere4 ,it   
also often ensues when the roots of     
plants in the open are waterlogged1     
owing to the stagnant water not only    
driving air from the root-hairs but     

accumulating dissolved substances which 
poison the plant4 ,trees frequently thus
 suffer from wet feet when their roots  
have penetrated down to a sodden        
impervious subsoil4  ,yellowing         
accompanied by ,wilting is a predominant
 symptom in most cases where            
transpiration is more active than       
root-absorption beyond a certain limit1 
as is well known in cases of prolonged  
drought4 ,it may also be caused in      
evergreens by the foliage transpiring   
actively in bright ,january weather1 for
 instance1 while the ground is frozen   
and the chilled root-hairs cannot       
absorb4  ,in other cases similar        
appearances are traceable to insects    
devouring the roots1 e4g4 wireworms1 and
 the malady is sometimes enhanced by    
their accumulations so fouling the wet  
soil that the roots die off1 owing to   
want of oxygen and to the excess of     
carbon-dioxide and poisonous matters4   
,yellowing may also result from the     
presence of poisonous or acid gases in  

the atmosphere or soil1 such as         
chlorine1 hydrochloric acid1 sulphurous 
acid1 etc41 in the neighbourhood of     
chemical works1 or from the escape of   
coal-gas in streets1 etc41 points of    
importance in connection with the use of
 fungicides and insecticides4           
,yellowness is the prevailing symptom in
 many cases of fungus attack of the     
roots or collar of the plant1 the       
resulting stoppage of transpiration     
being also sometimes supplemented by    
rotting of the roots1 and the consequent
 deprival of oxygen and accumulation of 
foul gases4 ,in other cases ,fungi1 and 
even ,bacteria1 have been found to have 
made their way into the principal       
vessels1 the lumina of which they stop  
up1 thus reducing the transpiration     
current4  ,certain insects may also     
induce a general yellowing and wilting  
of plants by entering or destroying the 
tissues concerned in the                
transpiration--e4g4 ,oniscus1 the ,frit 
,fly1 and ,cecidomya1 the ,hessian ,fly1

 which attack young winter wheat within 
the sheaths and cause the plants to turn
 yellow and wilt4  ,albinism and        
,variegation are apparently due to      
causes totally different from any yet   
mentioned4 ,church's analyses have shown
 that albino leaves contain more water  
and less organic matter than green ones 
of the same plants1 but not necessarily 
less ash constituents4 ,the composition 
of the ash points to there being more   
potash and less lime in the white organs
 than in the green ones1 and1 speaking  
generally1 the former are related to the
 latter much as young leaves are related
 to mature ones4  ,the whole matter is  
complicated by the behaviour of certain 
variegated plants--e4g4 ,ribbon grass1  
,calla1 ,abutilon1 which are usually    
regarded as partial albinos4  ,meyen    
showed long ago that such variegated    
plants1 if grafted on green ones1 may   
induce the development of variegated    
leaves on both scion and stock1 and     
,morren and others have not only        

confirmed this but have also shown that 
variegation may be inherited through the
 seed4 ,nevertheless some care has to be
 taken with many of these variegations  
lest rich soil1 bright light1 and other 
favourable treatment favour the         
restitution of the green colour4 ,these 
facts may be interpreted in various     
ways4 ,some disturbance of physiological
 functions of the roots1 due to         
unfavourable conditions of soil1 may be 
the cause2 but ,beijerinck has lately   
published some results which show that  
some of these albino diseases can be    
induced by inoculating normal plants    
with the juice of spotted ones even     
though such juice has been filtered     
through porcelain1 and concludes that a 
contagium fluidum vivum of the nature of
 a transmissible enzyme is the agent    
which disturbs the physiology of the    
infected cells4  ,koning1 while         
confirming these results in the main1   
refers them to a micro-organism so small
 that it traverses the porcelain filter4

  ,upheaval of seedlings4--,this is a   
common form of injury1 resulting in     
death by drought and exposure1          
especially in seedling pines1 wheat1    
etc41 in soils exposed to alternate     
freezing and thawing during spring when 
there is no snow to protect the plants4 
,the soil freezes during the night1 and 
during the thaw next day water          
accumulates just below the surface4 ,the
 freezing is then repeated1 and1 partly 
owing to the expansion of the forming   
ice and partly to the mechanical effect 
of the ice-crystals in the interstices1 
the surface of the soil is lifted and   
draws the roots with it4 ,during the    
succeeding thaw the soil particles fall 
away from the lifted root-fibres1 and   
frequent repetition of these processes  
results in such complete exposure of the
 roots to the full sun that the plantlet
 falls over and wilts4  ,exposure of    
roots is also sometimes effected by     
winds displacing sandy soils liable to  
shifting in dry weather1 and the        

resulting wilting of the plants thus    
exposed at their roots may be           
supplemented by damage due to the       
repeated impact of the wind-driven sharp
 grains of sand1 which act like a       
sand-blast and erode the tissues4  ,in  
many of the cases given above the       
principal result is the weakening or    
destruction of the chlorophyll action4  
,this means a loss of                   
carbohydrates--sugars1 starches1        
etc4--and in so far a starvation of the 
plant4 ,the injurious effects are       
quantitative and cumulative3 if large   
areas of foliage are concerned1 or if   
the effect lasts a long time1 the plant 
suffers from loss of food1 and may die4 
,in those cases where the effect is due 
to the cutting off of supplies at the   
roots1 and where the yellowing is a     
secondary symptom1 the disease is more  
general in character1 and recovery is   
often impossible1 because the loss of   
water cannot be compensated1 and the    
results may be further complicated by   

the gradual penetration of poisonous    
matter into the cells4 ,it is frequently
 necessary1 though sometimes very       
difficult1 to decide which is the       
primary and which secondary 7or         
tertiary1 etc47 symptoms in the order of
 their importance1 and the diagnosis may
 be complicated by a number of accessory
 factors which it is impossible to treat
 generally4   ,,notes ,,to ,,chapter    
,,xix4       ,the principal cases here  
described are dealt with in works on    
plant physiology1 and in the works of   
,sorauer and ,frank      already        
referred to4       ,as regards damage   
due to uprooting of seedlings by frost1 
see      ,fisher1 ,forest ,protection   
7,engl4 ed4 of ,hess' ,forstchutz71     
in ,schlich's ,manual of ,forestry1     
,vol4 ,,iv41 #ahie1 pp4      #dci-ddb4  
,on ,albinism1 see ,church1 ,a ,chemical
 ,study of ,vegetable      ,albinism1   
,journ4 ,chem4 ,soc41 #ahgi1 #ahhj1     
#ahhf4       ,beijerinck's results are  
contained in his paper1 ,ueber ein      

,contagium vivum fluidum1 etc4 7with    
,english abstract71 in      ,verhandl4  
d4 ,kon4 ,akad4 v4 ,wetensch1 te        
,amsterdam1 #ahih4      ,koning's paper 
is in ,zeitschr4 f4 ,pflanzenkrank41    
,vol4 ,,ix41      #ahii1 p4 #fe4 ,see   
also ,nature1 ,oct4 #aa1 #aijj1 p4 #egf4
     ,,chapter ,,xx4  ,,symptoms ,,of   
,,disease 7,continued74       ,spotted  
leaves--,the colours of spots--,white1  
yellow1 brown1      and black spots on  
leaves--,parti-coloured spots--,the     
browning1      etc41 of leaves4         
,discoloured spots or patches on the    
herbaceous parts of plants1 especially  
leaves1 furnish the prominent symptoms  
in a large class of diseases1 due to    
many different causes1 and although we  
cannot maintain this group of symptoms  
sharply apart from the last1 as seen    
from the considerations on albinism1 it 
is often well marked and of great       
diagnostic value4 ,by far the greater   
number of spot-diseases are due to      
fungi1 but this is by no means always   

the case4 ,the most generally useful    
method of subdividing the classes1      
though artificial like all such         
classifications1 will be according to   
the colour of the spots or flecks1      
which1 moreover1 are usually found on   
the leaves4 ,it is necessary to note1   
however1 that various conditions may    
modify the colour of spots on leaves4   
,many fungi1 for instance1 induce       
different coloured spots according to   
the age of the leaf or other organ      
attacked1 or according to the species of
 host1 the weather1 etc4 ,moreover the  
spots due to these parasites are        
frequently yellow when young and some   
other colour1 especially brown or black1
 when older4  ,scale is the name given  
to the characteristic shield-like       
insects 7,mytilaspis1 ,aspidiotus1 etc47
 which attach themselves to branches of 
,apples1 ,pears1 ,oranges1 ,camellias1  
and numerous other plants1 and suck the 
juices4 ,it is the female insect which  
has the body broadened out into the     

scale1 under which the young are brought
 up4 ,enormous damage has been done by  
some forms--e4g4 the ,san ,jose scale in
 the ,united ,states4  ,the superficial 
resemblances of the patches of eggs of  
some ,lepidoptera to ,aecidia and other 
fungi may be noted in passing--e4g4     
,bombyx neustria on ,apple twigs1       
,aporia ,crataegi4  ,white or greyish   
spots are the common symptom marking the
 presence of many ,peronosporeae and    
,erysipheae in or on leaves1 e4g4       
,peronospora ,trifoliorum1 ,p4          
parasitica on ,crucifers1 etc41 and     
,sphaerotheca on ,hops2 also ,septoria  
piricola1 ,cystopus1 ,entyloma          
,ranunculi1 etc4  ,white spots are also 
caused by insects such as ,tetranychus  
7red spider7 on ,clover and other       
plants4  ,yellow1 or ,orange-coloured   
,spots4 ,in cases where these occur on  
leaves1 and in the case of grasses1     
etc41 on the leaf sheaths as well1 they 
commonly indicate the presence of       
,uredineae1 and sections under the      

microscope will show the mycelium in the
 tissues beneath4 ,species of ,uromyces1
 ,puccinia1 etc41 in the ,uredo state   
have the spots powdery with spores2     
,aecidia show the characteristic cluster
 cups1 and so forth4 ,these spots are   
often slightly pustular1 and in some    
cases markedly so4  ,other fungi also   
induce yellow spots on leaves--e4g4     
,phyllosticta on ,beans1 ,exoascus on   
,poplars1 ,clasterosporium on ,apricot  
leaves1 ,synchytrium ,succisae on       
,centaurea1 etc4  ,yellow spots are also
 a frequent symptom of the presence of  
,aphides1 of ,red ,spider1 etc4 ,thus   
the minute golden yellow spots sometimes
 crowded on ,oak leaves are due to      
,phylloxera punctures4  ,yellow patches 
are formed on the large leaves of       
,arisarum by a species of parasitic     
,alga1 ,phyllosiphon1 which lives in the
 mesophyll4 ,many tropical leaves are   
spotted yellow by epiphytic ,algae--e4g4
 ,cephaleuros4  ,it must be noticed that
 many fungi produce yellow spots or     

flecks in the earlier stages1 which turn
 brown or black as the fructifications  
appear1 e4g4 ,dilophia graminis1        
,rhytisma acerinum4  ,the yellow-spotted
 leaves of ,farfugium grande 7,senecio  
,kaempferi7 are so like those of        
,petasites attacked with ,aecidium in   
its early stages1 that an expert might  
be deceived until the microscopic       
analysis was completed4  ,red spots1    
varying from rusty or foxy red to bright
 crimson1 are the symptomatic           
accompaniment of several fungi1 the     
former often characterising the         
teleutospore or aecidium stage of       
,uredineae--e4g4 ,aecidium              
,grossulariae--the latter sometimes     
indicating the presence of              
,chytridiaceae4  ,red spots are also    
caused by ,gloeosporium ,fragariae on   
,strawberry leaves1 ,polystigma rubrum  
on ,plums4  ,crimson spots on ,apple and
 ,pear leaves are also due to           
,phytoptus3 they turn brown later4      
,brown spots or flecks1 varying in hue  

from dull slaty brown to deep red       
browns1 are a common symptom of ,fungus 
and ,insect diseases1 the colour often  
indicating the death of the tissues1    
rather than any special peculiarity of  
the action of the parasite4 ,good       
examples are furnished by the           
,potato-disease1 and by ,peronospora    
viticola1 ,sphaerella vitis and other   
disease-fungi of the ,grape ,vine4 ,the 
teleutospore stage of many ,uredineae   
also occurs in deep brown spots4  ,black
 spots and flecks are exceedingly common
 symptoms of the presence of fungi1 e4g4
 ,fusicladium on ,apples and ,pears1 and
 the pycnidial and ascus stages of many 
,ascomycetes--e4g4 ,phyllachora         
graminis4 ,the teleutospore stages of   
species of ,puccinia1 ,phragmidium1     
etc41 are also so deep in colour as to  
appear almost black4  ,scab on ,pears is
 due to the presence of ,fusicladium1   
which indurates the outer skin of the   
fruit causing it to crack under pressure
 from within1 and to dry up1 the deep   

brown to black patches of fungus        
persisting on the dead surface4  ,black 
spots on grasses and sedges are caused  
by ,ustilagineae1 and are commonest in  
the grain1 the soot-like powdery spores 
7,smut7 being very characteristic4      
,ustilago longissima induces black      
streaks on the leaves4 ,many of these   
fungi cause distortions or pustules on  
leaves and other organs4  ,brown and    
black leaf spots are frequently         
furnished with concentric contours      
arranged round a paler or other coloured
 central point--e4g4 ,cercospora on     
,beans1 ,ascochyta on ,peas4  ,brown    
spots with bright red margins are formed
 in young ,beans by ,gloeosporium4      
,species of ,fumago1 ,herpotrichia1     
etc41 may cover the entire surface of   
the leaf with sooty patches1 or even    
weave the leaves together as if with    
black spider-webs4  ,mal nero of the    
,vine is a particular case of black     
spotting and streaking of the leaves for
 which no satisfactory explanation is as

 yet to hand4 ,as with ,chestnuts1      
,walnuts1 and other plants containing   
much tannin1 the dark spots appear to be
 due to this substance1 but whether the 
predisposing cause is a lack of some    
ingredients in the soil1 or some        
temperature reaction1 or fungi at the   
roots1 is as yet unknown4 ,the most     
recent explanation puts the disease down
 to the action of bacteria1 but the     
results obtained by different workers   
lead to uncertainty4  ,the dying back of
 leaves1 especially of grasses1 from the
 tip1 is usually accompanied by a       
succession of colours--yellow1 red1     
brown1 to black--and is a common symptom
 of parching from summer drought2 and   
spots of similar colours1 frequently    
commencing at the margins of leaves1 are
 characteristic symptoms of the         
injurious action of acid gases in the   
air4  ,brown and blackish spots on      
,pears are caused by a species of       
,thrips4  ,in many cases the minute     
spots of ,rust-fungi on one and the same

 leaf are bright orange yellow 7uredo71 
deep brown1 or almost purple-black      
7teleutospores71 foxy-red brown 7older  
uredospores71 or dead slaty black where 
the old teleutospores have died         
off--e4g4 ,uromyces ,fabae on ,beans1   
,u4 ,pisi on ,peas1 etc4                
,parti-coloured leaves4--,the leaves    
sometimes start shrivelling with red    
edges1 while yellow1 red1 and finally   
brown and black blotches appear on the  
lamina1 from no known cause--e4g4       
,vines4 ,in other cases similar mimicry 
of the autumnal colouring of leaves     
results from the action of acid gases4  
,burning is a common name for all cases 
where the leaves turn red or red-brown  
in hot1 dry weather1 and many varieties 
are distinguished in different countries
 and on different plants1 because       
species react dissimilarly4 ,the primary
 cause is usually want of               
water--drought4  ,foxy leaves are a     
common sign of drought on hot soils1 and
 the disease may usually be recognised  

by the gradual extension of the drying  
and fox-red colour proceeding from the  
older to the younger leaves1 and from   
base to apex--e4g4 ,hops4  ,coppery     
leaves4--,the leaves of the ,hop1 etc41 
may show yellow spots and gradually turn
 red-brown--copper-coloured--as they    
dry2 the damage is due to ,tetranychus1 
the so-called ,red ,spider4 ,these cases
 must of course be carefully            
distinguished from the normal           
copper-brown of certain varieties of    
,beech1 ,beet1 ,coleus1 etc4            
,silver-leaf4--,the leaves of ,plum1    
,apple1 and other fruit trees often     
obtain a peculiar silvery appearance in 
hot summers1 the cause of which is      
unknown4  ,discolorations in the form of
 confluent yellow and orange patches1   
etc41 resembling variegations1 are not  
infrequently due to the ravages of ,red 
,spider and mites--e4g4 on ,kidney      
,beans4  ,sun-spots4--,yellow spots1    
which may turn brown or black according 
to the species of plant affected and the

 intensity of the action1 are often     
caused by the focussing of the solar    
rays by lens-like thickenings due to    
inequalities in the glass of            
greenhouses1 or by drops of water on    
them or on other leaves1 e4g4 ,palms1   
,dracaena1 etc4 ,the action is that of a
 burning glass1 and extends throughout  
the leaf-tissues4 ,young grapes1 etc41  
may also be injured in this way4        
,water-drops on the glass can only act  
long enough to produce such injuries if 
the atmosphere is saturated4 ,the old   
idea that a drop on a leaf can thus     
focus the sun's rays into the tissues   
beneath is not tenable4  ,here again we 
see that the disease-agencies concerned 
in producing the symptoms described in  
this chapter1 agree for the most part in
 so far that the principal effect is    
generally the disturbance of chlorophyll
 action in the spots or flecks on the   
leaves1 and the rendering useless of    
these areas so far as providing further 
food-supplies is concerned4 ,the effects

 may be due merely to the shading action
 of a parasite--e4g4 epiphytic fungi--or
 to actual destruction of the tissues   
invaded--e4g4 by endophytic fungi--or   
the tissues may be burnt1 poisoned1 etc4
 ,in so far the results are again       
quantitative and cumulative1 and the    
amount of damage depends on the number  
and size of the spots or other areas    
affected1 and the proportion of foliage 
involved1 as well as the length of time 
the injurious action is at work4 ,but1  
again1 it must be remembered that       
several symptoms may co-exist1 and      
matters may be complicated by the spread
 of the destructive agent1 or its       
consequences1 to other parts1 and in    
some cases we are quite uninformed as to
 the true nature of the disease4        
,,notes ,,to ,,chapter ,,xx4            
,further information regarding these    
leaf-diseases will be      found in     
special works dealing with the fungi and
 insects      which cause them4 ,in     
addition to works already quoted1 the   

reader may also be referred for ,fungi  
to ,massee1 ,a ,textbook      of        
,plant-diseases caused by ,cryptogamic  
,parasites1 ,london1      #ahii2 or     
,prillieux1 ,les ,maladies des ,plantes 
,agricoles1      #ahie4 ,see also       
,marshall ,ward1 ,coffee-leaf ,disease1 
,sessional      ,papers1 ,,xvii41       
,ceylon1 #ahha1 and ,journ4 ,linn4      
,soc41 ,vol4      ,,xix41 #ahhb1 p4     
#bii4       ,the question of ,sun-spots 
has been dealt with by ,joennson in     
,zeitschr4 f4 ,pflanzenkrankh41 #ahib1  
p4 #ceh4     ,,chapter ,,xxi4           
,,artificial ,,wounds4       ,the nature
 of wounds and of healing               
processes--,knife wounds--      ,simple 
cuts--,stripping--,cuttings--,branch-stu
mps and pruning--                       
,stool-stumps--,ringing--,bruises4      
,wounds4--,all the parts of plants are  
exposed to the danger of wounds1 from   
mechanical causes such as wind1 falling 
stones or trees1 hail1 etc41 or from the
 bites of animals such as rabbits1      

worms1 and insects1 and although such   
injuries are rarely in themselves       
dangerous1 they open the way to other   
agencies--water1 fungi1 etc41 which may 
work great havoc2 or the loss of the    
destroyed or removed tissues is felt in 
diminished nutrition1 restriction of the
 assimilative area1 or in some other    
way4  ,we have seen that living cells   
die when cut1 bruised1 or torn2 and that
 the cells next below in a layer of     
active tissue are stimulated by the     
exposure to increased growth and        
division1 and at once produce a layer of
 cork1 the impervious walls of which    
again protect the living cells beneath4 
,this is found to occur in all          
cell-tissues provided the cells are     
still living1 and it matters not whether
 the wound occurs in the mesophyll of a 
leaf1 the storage parenchyma of a       
,potato-tuber1 the cortex of a root or  
stem1 or in the fleshy parts of a young 
fruit1 the normal effect of the wound is
 in all cases to call forth an          

elongation of the uninjured cells       
beneath1 in a direction at right angles 
to the plane of the injured surface1    
which cells then divide by successive   
walls across their axis of growth3 the  
layers of cells thus cut off are then   
converted into cork1 by the suberisation
 of their walls4 ,further changes may   
then go on beneath the protective layer 
of wound-cork thus produced1 and these  
changes vary according to the nature of 
the cells beneath3 the cambium forms new
 wood1 the medullary rays similar rays1 
cortex new cortex1 and so on4           
,knife-wounds4--,artificial cuts in     
stems are easily recognised and soon    
heal up unless disturbed4 ,several      
cases1 differing in complexity1 are to  
be distinguished4 ,the simplest is that 
of a longitudinal1 oblique1 or          
horizontal short cut in which the point 
of the knife severs all the tissues of  
the stem down to the wood4 ,the first   
effect usually observed is that the     
wound gapes1 especially if longitudinal1

 because the cortex1 tightly stretched  
on the wood cylinder1 contracts         
elastically4 ,this exposes the living   
cortex1 phloem and cambium to the air1  
and such tissues at once behave as      
already described above3 the cells      
actually cut die1 those next below grow 
out under the released pressure1 and    
these give rise to cells which become   
cork4 ,as the growth and cell-division  
continue in the cells below this thin   
elastic cork-layer1 they form a soft    
herbaceous cushion or callus looking    
like a thickened lip to each margin of  
the cut4 ,each lip soon meets its       
opposite neighbour1 and the wound is    
closed over1 a slight projection with a 
median axial depression alone appearing 
on the surface4 ,the depression contains
 the trapped-in callus-cork squeezed    
more and more in the plane of the cut as
 the two lips of callus press one       
against the other1 and sections across  
the stem and perpendicular to the axis  
of the cut show that this thin cork1    

like a bit of brown paper1 alone        
intervenes between the cambium1 phloem  
and cortex respectively of each lip1 as 
each layer attempts to bridge over the  
interval4 ,if the healing proceeds      
normally1 these layers1 each pressing   
against the trapped cork-film1 and      
growing more and more in thickness1     
shear the cork-layer and tear its cells 
asunder1 and very soon we find odd cells
 of the cambium of one lip meeting      
cambium cells of the other1 phloem      
meeting phloem1 and cortex cortex1 and  
the normal thickening of the now fused  
layers previously separated by the knife
 goes on as if nothing had happened1 the
 only external sign of the wound being a
 slight ridge-like elevation1 and1      
internally1 traces of the dead cells and
 cork trapped here and there beneath the
 ridge4 ,when the conjoined cambium     
resumes the development of a continuous 
layer of xylem and phloem1 no further   
trace of the injury is observable1      
unless a speck of dead cells remains    

buried beneath the new wood1 and        
indicates the line where the knife point
 killed the former cambium and scored   
the surface of the wood in making the   
wound4  ,stripping4--,now suppose that1 
instead of a mere slit with the         
knife-point1 a strip of bark is removed 
down to the wood4 ,exactly the same     
processes of corking and lip-like callus
 formation at the edges of the wound    
occur1 but of course the occlusion of   
the bared wood-surface by the meeting of
 the lips occupies a longer time4       
,moreover1 the living cells of the      
medullary rays exposed by the wound on  
the wood-surface also grow out under the
 released pressure1 and form protruding 
callus pads on their own account4 ,in   
course of time the wood is again        
completely covered by the coming        
together over its face of these various 
strips of callus1 but two important     
points of difference are found1 as      
contrasted with the simpler healing of  
the slit-wound4 ,in the first place the 

exposed wood dries and turns brown1 or  
it may even begin to decay if moisture  
and putrefactive organisms act on it    
while exposed to the air2 and1 in the   
second place1 the normal annual layer of
 wood--or layers1 as the case may       
be--formed by the cambium only extends  
over that part of the stem where the    
cambium is still intact1 and is entirely
 wanting over the exposed area4 ,thus1  
if it takes two years for the cambium to
 extend across the wound1 a layer of    
wood will be formed all round the intact
 part of the stem1 from lip to lip of   
the cut tissues during the first year2  
then a second annual layer outside this 
will be formed during the second year1  
but extending further over the edges of 
the wound1 and nearly complete1 because 
the cambium has now crept further across
 the wounded surface to meet the        
opposite lip of cambium2 and during the 
third year1 when the cambium has once   
more become continuous over the face of 
the wound1 the annual wood layer will be

 complete4 ,but1 of course1 this last   
layer covers in the edges of the two    
previously developed incomplete         
wood-layers as well as the exposed and  
brown1 dry1 or rotten dead face of the  
wood4 ,it also covers up the trapped-in 
brown cork and any debris that          
accumulated in the wound1 and this      
blemish1 though buried deeper and deeper
 in the wood during succeeding annual   
deposits of wood-layers1 always remains 
to remind us of the existence of the    
wound1 the date of which can be fixed at
 any future time by counting the annual 
rings developed subsequently to its     
formation4 ,obviously1 also1 the        
deficiency of wood at this place makes  
itself visible on the outside by a      
depression4  ,cuttings4--,when a cutting
 of ,pelargonium1 ,willow1 or other     
plant is made1 we have a typical        
knife-wound1 the behaviour of which is  
very instructive in illustration of     
plant-surgery1 and may be most easily   
seen by keeping it in damp air instead  

of plunging it into sand or soil4  ,all 
the living cells actually cut or bruised
 turn brown and die as before2 those    
beneath--e4g4 the living pith1 medullary
 rays1 cambium1 phloem1 and cortex1 grow
 out under the released pressure and    
form a callus1 the outermost layer of   
which becomes cork1 while those below1  
abundantly supplied with food-materials1
 proceed to spread1 as if flowing over  
the surface of the cut wood1 and rapidly
 occlude the wound4 ,meanwhile new roots
 are formed adventitiously from the     
cambium just above the plane of section1
 and push out through the cortex into   
the damp air1 and if the cutting had    
been in soil it would now be capable of 
independent existence4 ,it is important 
to keep cuttings upright1 as the roots  
only spring from the lower end4 ,such   
cuttings can be obtained not only from  
stems1 but also from roots and even     
leaves4  ,callus-formation is not       
confined to the basal end of a cutting2 
it has nothing to do with position1 but 

is a reaction to the wound stimuli1     
independent of light1 gravitation1 etc4 
,as time goes on1 however1 the internal 
organisation of the erect cutting       
usually reacts on the callus at either  
end1 and roots only rise from the lower 
one1 while shoot-buds may form in the   
upper one1 though it is possible to     
bring about the formation of buds from  
the lower end also4  ,branch stumps4--,a
 more complex example is furnished by a 
branch cut off short some distance--say 
a foot--from the base1 where it springs 
from the trunk4 ,as before1 the         
immediate effect of the section is the  
formation of a callus from the cambium1 
phloem and cortex1 which begins to rise 
as a circular occluding rim round the   
wood4 ,the transpiration current in the 
trunk1 however1 is not deflected into   
the #ab inches or so of amputated       
branch1 because there are no leaves to  
draw the water up it1 and so the stump  
dries up and the cortex and cambium die 
back to the base1 leaving the dead wood 

covered with shrivelled cortical tissues
 only4 ,this dead stump gradually rots  
under the action of wet1 fungi1 and     
bacteria1 and since the pith and        
heart-wood afford a ready passage of the
 rot-organisms and their products into  
the heart of the trunk1 we find in a few
 years a mere stump of touch-wood and   
decayed bark1 which falls out at the    
insertion like a decayed tooth1 leaving 
a rotten hole in the side of the trunk4 
,if1 however1 instead of allowing the   
basal part of the amputated branch to   
protrude as a stump1 we cut it off close
 to the stem1 and shave the section     
flush with the normal surface of the    
latter1 the callus formed by the        
cambium1 etc41 rapidly grows over the   
surface1 and soon forms a layer of      
cambium continuous with that of the rest
 of the stem4 ,the wound heals1 in fact1
 much as if it were a strip-wound1 and  
beyond a slight prominence for a year or
 two no signs are visible from the      
outside after the occlusion4 ,of course 

these matters depend on the relative    
thickness of branch and stem1 and if    
much wood is exposed the dangers of rot 
and a resulting hollow in the stem are  
increased4 ,it is interesting to note   
how much thicker the callus lips are at 
the sides of the wound than above and   
below1 owing to differences in the      
distribution of the nutrient materials4 
,stool-stumps4--,when a tree is felled1 
the stump may1 if the section is close  
to the ground and kept moist1 begin to  
form a thick rim-like callus round the  
wood1 in which adventitious buds soon   
make their appearance1 and grow out into
 so-called ,stool-shoots4 ,the products 
of assimilation of these1 and the stores
 accumulated in the stump1 often suffice
 to feed the callus sufficiently to     
enable it to grow over and completely   
occlude the wound1 if the wood surface  
is not too large1 or so long exposed    
that rotting processes have meanwhile   
set in4  ,ringing4--,if the strip of    
cortical tissues and cambium is removed 

all round the stem1 exposing the wood in
 a form of a ring1 complications may    
ensue owing to the following            
circumstances4 ,a well-marked callus    
appears at the upper edge of the wound1 
because1 the transpiration current up   
the young wood not being stopped1 plenty
 of water and salts from the soil can   
reach the leaves2 but the nutritive     
materials supplied by the latter are    
accumulated at the upper lip of the     
wound owing to the stoppage there of    
their descent in the phloem1 cortex1    
etc4 ,no such callus-lip appears at the 
lower margin of the wound owing to want 
of these supplies4 ,consequently the    
occlusion and healing of the ring-wound 
only takes place from above downwards1  
and if the ring of cortical tissues     
removed is a broad one1 the healing may 
be a long process1 or may even be       
indefinitely delayed1 a thicker and     
thicker callus projecting over from     
above4 ,for similar reasons no annual   
wood layers are formed below1 but only  

above the wound1 and thus the branch or 
tree may die4 ,the latter contingency is
 the more likely the further up the tree
 the ringing takes place1 owing to the  
risk of drying up which threatens the   
exposed wood1 and to the consequent     
interruption of the transpiration       
current1 and the likelihood that lateral
 shoots below the wound may divert the  
water to their own leaves4 ,if the      
ringing occurs low down on a stem1 and  
the environment remains damp1 the upper 
thick callus may put out new roots2 the 
part above the wound then behaves like a
 cutting4 ,if the ringing is done on a  
young and vigorous branch of an old     
tree1 the lower lip may receive supplies
 from the leaves of branches below the  
wound1 or from shoots which spring from 
adventitious buds close to it1 and the  
wound may heal over normally4 ,such     
healing may be rendered more certain by 
keeping the wounded surface moist--e4g4 
by means of damp moss1 and so           
encouraging the formation of            

callus-bridges from the medullary rays4 
,if on ringing a tree or a branch the   
young wood is removed as well as the    
cambium and cortical layers1 the death  
of the parts above the wound is almost  
certain1 owing to the stoppage of the   
transpiration current3 the exceptions to
 this rule depend simply on the         
existence of other channels of          
communication1 such as internal phloems1
 very thick sap-wood1 and so forth4     
,bruises4--,if a branch or woody stem is
 struck sharply1 with a hammer1 for     
instance1 the bruised cortex1 phloem and
 cambium are killed by the blow1 and the
 general effect is as if these tissues  
had been removed at that spot by the    
knife1 but with the following           
complications4 ,the bruised cortical    
tissues rapidly dry as they perish1 and 
may adhere to the wood below4           
,consequently the still sound parts     
bordering on the wound are not released 
from pressure1 but1 on the contrary1    
have to advance towards each other over 

the surface of the wood under still     
greater pressures1 in part due to the   
tightening of the whole cortex as the   
dead parts dry and contract1 and in part
 due to the above-mentioned adherence of
 the latter to the wood4 ,it results    
from this that such wounds heal very    
slowly and badly1 and when the killed   
patch at last ruptures1 wound-fungi1    
insects1 and other injurious agencies   
may get in and do irreparable damage1 as
 has been found to occur in cases where 
such wounds have been made in striking  
trees to shake down insects1 fruit1 etc4
   ,,notes ,,to ,,chapter ,,xxi4        
,the essential facts regarding wounds   
and healing by occlusion      are given 
in ,marshall ,ward1 ,timber and some of 
its ,diseases1      #ahhi1 chapters     
viii4 and ix41 and in ,laslett1 ,timber 
and      ,timber ,trees1 #ahid1 chapters
 iv4 and v4 ,more detailed              
treatment will be found in ,frank1      
,krankh4 d4 ,pflanzen1 ,b4 #a4      cap4
 #b1 where the special literature is    

collected4 ,the reader      may also    
consult ,hartig1 ,diseases of ,trees1   
,engl4 ed4 #ahid1      pp4 #bbe-bfi4    
,,chapter ,,xxii4  ,,natural ,,wounds4  
,burrows and excavations4               
,bark-boring--,wood-boring--,wood       
fungi--,leaf-miners--,pith              
flecks--,erosions4 ,skeleton leaves--   
,irregular erosions--,shot holes4 ,frost
 cracks--,strangulations--      ,spiral 
grooving4   ,natural wounds are produced
 in a variety of ways during the life of
 the plant1 and1 generally speaking1 are
 easily healed over by the normal       
process if the area destroyed is not too
 large1 and the parts remaining         
uninjured are sufficiently provided with
 foliage1 or with supplies of           
food-materials stored up in the roots1  
rhizomes1 medullary rays1 etc41 to feed 
a vigorous callus4  ,the nature of such 
wounds and the mode of healing are      
explained by what we know of artificial 
wounds1 and it only remains to point out
 that the principal danger of ordinary  

wounds is not so much the direct        
traumatic action1 because the simpler   
organisation of the plant does not      
involve matters connected with shock1   
loss of blood1 etc41 as in animals2 the 
danger consists1 rather1 in their       
affording access to other injurious     
agents1 especially fungi1 and the       
treatment of wounds frequently resolves 
itself into cutting or pruning in order 
to get clean surfaces which can heal    
readily4  ,wounds on leaves imply loss  
of foliar surface--i4e4 of chlorophyll  
action--and the remarks on page #aic    
apply4  ,burrows may be taken as        
comprising all kinds of tunnel-like     
excavations in the various organs of    
plants1 including those cases where     
insects burrow into hollow stems of     
grasses1 etc41 as indicated by the      
perforations they make in the outer     
tissues4  ,bark-boring is done by many  
species of beetles1 especially          
,scolytidae1 which excavate             
characteristically formed branching     

passages tangentially in the inner bark 
of ,conifers and other trees4 ,some of  
them also bore down to the surface of   
the sap wood 7e4g4 ,tomicus bidentatus7 
or even burrow right into the latter    
7e4g4 ,t4 lineatum74 ,it commonly       
happens that the external apertures show
 up clearly1 owing to the brown dust and
 excrement1 sometimes accompanied by    
turpentine1 which exude from them4 ,many
 of these ,bark beetles only attack     
trees which are already injured by fire1
 lightning1 etc42 possibly they cannot  
bore through a cortex which swamps them 
with sap1 as a vigorous one might do4   
,wood-boring is also done by many of the
 bark-beetles as well as by ,longicorns1
 e4g4 ,saperda in ,poplars and ,willows1
 the young shoots of which often show   
characteristic swellings with lateral   
holes indicating the points of exit4    
,from the external apertures comminuted 
wood1 like saw-dust1 is frequently      
ejected in quantity and betrays the     
presence of the insects4 ,certain       

wood-wasps 7,sirex7 and the larvae of   
moths 7,cossus7 also make large         
perforations in the wood of ,willows and
 other trees1 often destroying it       
completely4 ,in the case of these larger
 borers1 whose tunnels may be as broad  
as the little finger1 the foul smell as 
well as abundant saw-dust betray the    
evil4  ,excavations in wood are by no   
means caused only by insects3 several of
 the larger ,hymenomycetes--,stereum1   
,thelephora1 ,polyporus1 etc4--tunnel   
the timber in characteristic ways and   
often after a fashion very suggestive of
 insects4 ,they usually obtain access   
through fractures4  ,tunnels in leaves  
are invariably due to the activity of   
miners belonging to the smaller moths   
and beetles--e4g4 ,tinea1 ,orchestes1   
etc4--the larvae of which eat out the   
mesophyll but leave the covering        
epidermis or cuticle untouched1 and     
since the insect bores forwards only1 in
 an irregular track1 and leaves its     
excrement in the winding passage1 the   

effect is very characteristic4  ,whitish
 leaf tunnels in ,peas are excavated by 
,phytomyza4  ,characteristic foxy-red   
tunnels are mined in the leaves of      
,apples by ,lyonetia1 ,coleophora1 etc4 
,falling of fruit1 of ,apples1 ,plums1  
,apricots1 etc41 before they are ripe1  
is frequently due to insects1 of which  
the various species of ,grapholitha or  
,carpocapsa are conspicuous3 the fallen 
fruits show a small hole leading by a   
labyrinth of passages to the core or    
stone1 and in which the grub and its    
excrement are visible4 ,the cutting off 
of the vascular bundles and disturbance 
of the water supply only partly explain 
the premature fall4  ,pith-flecks are   
minute brown specks or patches found in 
the wood-layers of many trees1 and      
consist of dead parenchymatous          
thick-walled cells1 reminding one of the
 structure of pith4 ,they are explained 
as due to the borings of minute insects1
 ,diptera or ,beetles1 the larvae of    
which pierce the cortex and phloem and  

bore their way into the cambium4 ,the   
latter then occludes the tunnels by     
filling them up with cells1 and         
continuing its wood-forming activity    
gradually buries them deeper and deeper 
in the wood4 ,such pith-flecks are      
common in ,willow1 ,birch1 ,alder1      
,sorbus1 etc4 ,it is possible that they 
may be due to other causes also in other
 trees4  ,erosions or irregular wounds  
on leaves are caused by large numbers of
 grubs and caterpillars and other       
insects1 such as earwigs1 as well as    
slugs1 snails1 and other animals2 but it
 must by no means be assumed that all   
marginal leaf wounds1 for instance1 are 
caused by animals1 since many fungi     
which rot the tissues1 as explained     
below 7p4 #bjh71 also cause such        
erosions1 the putrescent parts falling  
out--e4g4 the ,potato disease4          
,skeleton leaves frequently result from 
the ravages of caterpillars1 which leave
 the coarser ribs and veins untouched1  
but much finer skeletons with the minute

 veins almost intact may be found on    
plants infested with certain            
insects--e4g4 ,selandria on ,cherries4  
,skeletonised patches on ,cherry leaves1
 often pink or brown-pink1 are eaten out
 by this grub4  ,shot-holes are         
perforations in leaves presenting the   
appearance1 from their more or less     
rounded shape1 of gunshot wounds4 ,they 
may be due to insects which bore through
 the young leaves while still folded in 
the bud--e4g4 ,willow ,beetle--or which 
gnaw out the tissue--e4g4 the ,beech    
,miner4 ,similar but usually more torn  
and irregular holes are eaten out by    
many caterpillars--e4g4 the ,cabbage    
,moth4  ,shot-holes on ,peas may be the 
work of ,thrips4  ,leaf perforations are
 commonly caused by severe hail-storms1 
the hail-stones beating right through   
the thin mesophyll4 ,certain chemicals  
used for spraying have also been known  
to cause shot-holes by killing the      
tissue beneath the standing drops4      
,there is1 however1 a class of          

shot-holes in thin leaves which are due 
to the action of minute fungi1 the      
mycelium of which so rots the tissues in
 a more or less circular area round the 
point of infection1 that1 in wet        
weather1 the decomposing mass falls out 
and leaves a round hole--e4g4 certain   
,chytridiaceae1 ,peronosporeae1         
,gloeosporium1 ,exoascus1 etc4 ,if dry  
weather supervenes these holes          
frequently dry at the edges1 and the    
leaves appear as if eaten out4          
,shot-holes in ,cherry1 ,walnut1        
,tobacco1 and ,plum leaves are due to   
,phyllosticta1 in ,cherry leaves also to
 ,clasterosporium1 and in ,potato leaves
 to ,haltica4  ,frost-cracks4--,the     
trunks of trees exposed to the          
north-east1 and occasionally with other 
aspects1 are apt to show longitudinal   
ridges which realise on a larger scale  
the features of healed wounds scored    
with a knife4 ,these wounds are due to  
the outer layers of wood losing water   
from their cell-walls as it congeals to 

ice in their lumina1 more rapidly than  
do the warmer internal parts of the     
trunk2 as this drying of the wood causes
 its shrinkage1 especially in the       
tangential direction1 the effect of a   
sudden frost and north-east wind is to  
rend the wood1 which splits             
longitudinally with a loud report1 as   
may often be heard in severe winters4   
,since the cortex and bark are ruptured 
at the same time the total effect       
resembles that of a deep knife-cut1 and 
the same healing processes result on a  
larger scale when the wood swells and   
closes up the wound again in spring4    
,but this recently-closed lesion is     
evidently a plane of weakness1 and if a 
similarly severe winter follows the     
wound reopens and again heals1 and so   
on1 until after a succession of years a 
prominent ,frost-ridge results1 which   
may finally heal completely if milder   
winters ensue or the tree be eventually 
protected4  ,strangulations4--,we are   
now in a position to understand the     

so-called strangulations which result   
when woody climbers1 telegraph wires1   
etc41 kill or injure trees by tightly   
winding round them4 ,if strong wire is  
twisted horizontally round a stem1 the  
growth in thickness of the latter causes
 the trapping of the cortex and cambium1
 etc41 between the wire and the wood1   
and a ringing process is set up in      
consequence of the death of the         
compressed tissues4 ,a callus then forms
 above the wound1 as in the case of true
 ringing by means of a cut1 and         
eventually bulges over the upper side of
 the wire3 in the course of years this  
overgrowth may completely cover in the  
wire1 and1 pressing on to the lower lip 
of the wound1 may at length fuse with   
the cambium below4 ,hereafter the       
thickening rings of wood are continuous 
over the buried wire4 ,the process is   
obstructed by all the impediments       
referred to in dealing with ringing1 and
 of course the stem thickens more above 
than below the wire4 ,if the sapwood is 

thin1 and the bark is so thick as to put
 great obstacles in the way of the      
junction of the upper and lower         
cambiums1 death may result--the tree is 
permanently ringed4 7,see p4 #bja47     
,spiral grooves are frequently met with 
where ,wood-bine or other woody climbers
 have twined round a young stem or      
branch1 the upper lip of the groove     
always protruding more than the lower4  
,if a kink or a crossing of two plants  
or branches of the twiner results in a  
complete horizontal ring1 the results   
are as in the above cases of ringing and
 strangulation4 ,naturally grooved      
walking sticks are often seen4  ,buried 
letters1 etc4--,these processes of      
healing by occlusion enable us to       
understand how letters of the alphabet1 
cut into the wood of trees1 come to be  
buried deep in the timber as successive 
annual rings cover them in more and     
more4 ,chains1 nails1 rope1 etc41 have  
frequently been found thus buried in    
wood4   ,,notes ,,to ,,chapter ,,xxii4  

,in addition to the notes to the last   
chapter1 the reader may      be referred
 to ,fisher in ,vol4 ,,iv4 of ,schlich's
 ,manual of      ,forestry1 ,chap4      
,,vi41 for an account of ,hess'         
excellent work      on ,boring ,beetles1
 etc4       ,the authority on           
,wood-fungi is ,hartig1 see especially  
his      ,zersetzungs-erscheinungen des 
,holzes1 the principal results      of  
which are condensed in his ,diseases of 
,trees already      referred to4 ,as    
regards ,pith-flecks1 the reader should 
consult ,frank1 ,krankh4 der ,pflanzen1 
,b4 ,i41 p4 #bab3 the      subject needs
 further investigation4     ,,chapter   
,,xxiii4  ,,excrescences4               
,herbaceous excrescences1 or            
galls--,erineum--,intumescences--       
,corky warts1                           
etc4--,pustules--,frost-blisters--,galls
 and ,cecidia      --,root nodules4     
,excrescences1 or out-growths of more or
 less abnormal character from the       
general surface of diseased organs1 are 

very common symptoms1 and widely        
recognised4 ,they are due to hypertrophy
 of the tissues while the cells are     
young and capable of growth1 and may be 
induced by a variety of causes1 among   
which the stimulus of insect-punctures  
and of the presence of insect eggs are  
best known2 but that of fungi1 though   
less widely recognised1 plays an equally
 important part1 and1 as we shall see1  
galls and other excrescences may be due 
to widely different agents4  ,galls or  
,cecidia are protuberances of the most  
varied shapes1 colours1 and sizes found 
on herbaceous parts attacked by insects1
 fungi1 etc4 ,in the simplest cases the 
insects only pierce and suck the young  
cellular tissue--e4g4 ,phytoptus1       
,aphides1 etc4--but in others the       
stimulus to hypertrophy starts by the   
puncture of the embryonic tissue of a   
leaf1 root1 etc41 by the ovipositor of  
the female insect1 which then lays an   
egg--e4g4 ,cynips1 ,cecidomyia1         
etc4--the presence of which appears to  

intensify the irritating action1 or such
 only occurs when the young larva       
escapes4  ,our knowledge of the primary 
cause of gall-formation amounts to very 
little4 ,generally speaking1 only       
embryonic or very young cellular tissue 
reacts1 and galls on adult leaves and   
branches have usually been initiated    
long before4 ,the same gall-insect may  
induce totally different galls on       
different plants1 or even on different  
parts of the same plant1 and different  
insects call forth different galls on   
any one plant4 ,these facts point       
clearly to the co-operation of both     
plant and insect in the gall-formation1 
and the best hypothesis yet to hand is  
to the effect that a gall is a          
hypertrophy of cells1 the normal        
nutrition1 growth1 and division of which
 have been disturbed owing to the action
 of some poison or other irritant       
derived from the insect1 or fungus1 or  
other organism4 ,attempts have been made
 to reproduce galls by injecting the    

juices of similar galls into the tissue1
 but as yet without success1 and this   
may point to the co-operation of        
mechanical irritation during the        
hypertrophy in normal gall-formation4   
,galls1 in the broad sense1 are not     
always preceded by a wound1 however4    
,insects on the outside of young tissues
 may cause such irritations that the    
parts in contact with the animal are    
arrested in their growth1 while those   
further away grow more rapidly--e4g4    
where ,mites1 etc41 cause puckers and   
leaf-rolling4 ,in true galls the        
hypertrophy may consist merely in the   
enlargement of cells already present1   
and no new cell-divisions and1 still    
less1 changes in the nature of the      
tissues result--e4g4 some pocket galls  
on ,viburnum1 ,pyrus1 etc41 and the     
hairy outgrowths of the epidermis known 
as ,erineum4 ,in other cases there is   
not only hypertrophy of existing cells1 
but new cell-divisions are instituted3  
these cell-divisions may be confined to 

the direction perpendicular to the      
epidermis1 and the tissues grow only in 
the direction of the surface1 producing 
puckerings--e4g4 the ,aphis galls on    
,ribes1 ,phytoptus galls of ,salvia1    
leaf galls on ,tilia1 ,acer1 ,alnus1    
etc41 and the curious galls on ,plums   
due to ,cecidomyia ,pruni1 and which    
must not be confounded with the pocket  
plums and similar galls due to ,exoasci4
  ,in a third series of cases1          
cell-divisions occur parallel to the    
surface of the leaf1 and galls are      
formed which grow in thickness1 and     
develop the most extraordinary and      
complicated new tissues--proteid-cells  
surrounding the egg or larva deposited  
inside1 followed by a protective layer  
of sclerenchyma encasing this food      
layer1 and around this again softer     
tissues which may assume the structures 
and functions of respiratory tissues1   
water-storing tissues1 starch           
reservoirs1 assimilatory1 or protective 
tissues of various kinds1 and over all  

may be a well-marked epidermis1 with    
stomata1 or cork with lenticels4  ,the  
chief seat of these hypertrophies       
and--what is more                       
remarkable--development of new tissue   
elements not found elsewhere in the     
leaves1 or even in the species1 is the  
mesophyll1 and various speculations and 
hypothesis have been founded on these   
curious phenomena4  ,erineum4--,the     
simplest excrescences on plants are     
certain hair-like developments of       
epidermal cells due to the irritation of
 species of ,phytoptus1 and similar     
insects which rise in clusters on the   
surfaces of leaves and by their colours1
 consistence1 arrangement in patches1   
spots1 etc41 so simulate fungi that     
,persoon was deceived by them and gave  
them the genus name ,erineum4 ,they     
occur on most of our trees1 e4g4        
,poplar1 ,lime1 ,oak1 and are very      
common in the ,tropics4 ,usually pale or
 even white at first1 they turn brown as
 the hair-like outgrowths die and lose  

their sap1 but since the latter may be  
bright coloured--yellow1 red1           
purple1--the patches are sometimes very 
conspicuous objects on smooth leaves4   
,in many cases these hairs exactly      
resemble in shape and other characters  
the abnormal root-hairs found on roots  
exposed to the effects of poisonous     
reagents1 or of unsuitable              
food-materials1 or the rhizoids         
developed from wounded ,algae1 etc4     
,intumescences are similar trichomatous 
outgrowths not associated with insects  
or fungi1 and due to some disturbance of
 the balance between transpiratory and  
assimilatory functions of their leaves1 
as indicated by the less localised      
occurrence and by their non-appearance  
when the plant is under favourable      
cultural conditions4 ,structures not    
unlike these have been artificially     
induced by exposure to particular       
lights1 and also by painting spots with 
dilute corrosive sublimate1 indicating  
that poisons may impel the epidermis    

cells to grow out abnormally4  ,corky   
warts4--,several forms of disease are   
known in which the pathological         
condition is expressed by the formation 
of cork in unwonted places and          
quantities4 ,the ,scab or ,scurf of     
,potatoes is a case in point4 ,the      
tissue of the lenticels absorbs water   
and the outermost cells are cut off by  
cork and die3 the cells below them burst
 the dead bark-like masses thus formed1 
and again cork is formed and cuts off   
the outer masses1 and the rough cork    
warts--,scab or ,scurf--are the result4 
,the causes predisposing to scab have   
been variously assigned to dampness1    
want of lime1 action of bacteria and    
fungi--e4g4 ,sorosporium1 ,oospora1     
,spongospora1--the latter making their  
way into the ruptured tissue of the     
lenticels and irritating the cells to   
further growth4  ,it seems probable that
 several different kinds of scab exist  
in ,potatoes1 as well as in roots--e4g4 
,beets1 and the whole subject needs     

further investigation4 ,the scab-like   
rough scaly bark of ,pear trees in dry  
districts may also be mentioned here4   
,cork-wings are well known on the young 
branches of ,elms1 ,maples1 etc41 some  
varieties of which have received        
specific names on this account4  ,corky 
excrescences on leaves occur            
occasionally in the ,gooseberry1 ,holly 
and other plants1 for which no cause has
 been discovered4  ,lenticels are also  
formed on some leaf-galls1 and are      
remarkable as being structures not      
normal on leaves4  ,pustules4--,this    
term may be employed generally for all  
slight upheavals of the surfaces of     
herbaceous organs1 which subsequently   
burst and give egress to the spores1    
etc41 of the organism causing them1 or  
merely fray away at the top if no       
organism is discoverable4 ,they are     
often due to fungi--e4g4 ,synchytrium1  
,protomyces1 ,cystopus1 and             
,ustilagineae1--and we may extend the   
use of the general term also to those   

cases where the stroma of the fungus    
itself bursts through the cortex of     
older parts and forms the principal part
 of the pustule--e4g4 ,monilia1 forming 
white or grey pustules on ,apples1      
,roestelia and other ,a,ecidia1 forming 
yellow or orange pustules on leaves1    
etc42 ,cucurbitaria and ,nectria 7red7  
breaking through the cortex of trees1   
and ,phoma and numerous other           
,ascomycetes which form black cushions4 
,pustules on the leaves of ,lysimachia1 
,ajuga1 etc41 are due to the parasitic  
,alga ,phyllobium4  ,cylindrical stem   
swellings are caused by ,calyptospora3  
they are due to the hypertrophy of the  
cortex of ,bilberry stems permeated by  
the hyphae4 ,epichloe1 which clothes the
 sheaths and halms of grasses with its  
stroma1 at first snowy white and later  
ochre-yellow as the perithecia form1 is 
another example4  ,the cylindrical layer
 of eggs of a moth such as ,bombyx on a 
twig must not be confounded with these  
cases4  ,frost-blisters are pustule-like

 uprisings of the cortex1 where the     
living tissues below have formed a      
callus-like cushion into the cavity     
beneath the dead outer parts of the     
cortex which were killed by the frost2  
they occur on the stems of young        
,apples1 ,pears1 etc4  ,galls in the    
narrower sense are tissue outgrowths    
usually involving deeper cell-layers4   
,they are so varied and numerous that   
classification is difficult4 ,for       
symptomatic purposes we may divide them 
as follows3  ,leaf-galls4--,a           
well-marked type is that of the         
pocket-galls or bladders in which the   
whole thickness of the leaf is as it    
were pushed up like a glove-finger at   
one spot1 so that if the upper surface  
of the leaf forms the outside of the    
gall the lower surface is its lining4   
,such galls are common on ,limes        
7,phytoptus71 ,glechoma 7,cecidomyia71  
,elms 7,tetraneura71 etc4 ,similar      
localised extension of the leaf surface1
 compelling it to rise up like a pocket1

 are caused by fungi--e4g4 ,taphrina on 
,poplars1 ,exoascus on ,birches1 etc41  
,exobasidium on ,bilberries1            
,rhododendrons1 etc4  ,another type is  
that of the ,gall-apple1 so well known  
on ,oaks1 where the spherical swelling  
is solid--except for the inner cavity   
containing the eggs--,neurotus1 ,cynips1
 ,hormomyia1 etc4 ,these are comparable 
in general characters to the nodules on 
roots4  ,fungus galls with similar      
external features when young are found  
on ,maize 7,ustilago ,maydis71 and      
betray their nature by the black powdery
 spores as they mature4  ,bud galls on  
,willows are due to ,cecidomyia1 which  
causes several internodes to swell out  
into a greenish barrel-shaped mass1 from
 which leaves may spring4  ,small       
irregular excrescences on ,willow stems 
are referred to ,phytoptus1 and another 
species of the same insect induces      
similar swellings on ,pines which are   
not surcharged with resin4  ,american   
,blight1 or ,woolly ,aphis1 on ,apples  

especially1 causes the tumour-like      
swellings covered with sticky white     
fluff1 which is a waxy excretion of the 
insect4 ,galls on ,pilea1 in ,java1 are 
due to an ,alga--,phytophysa4           
,root-nodules or nodosities are         
frequently caused by insects--e4g4      
,centhorhynchus1 a beetle which attacks 
,crucifers1 ,cynips and allied gallflies
 of ,oaks1 and the notorious            
,phylloxera4 ,but similar root-galls are
 produced by ,nematode worms1           
,heterodora1 on ,beets1 ,tomatoes1      
,cucumbers and numerous other plants1   
and by the ,slime fungus                
,plasmodiophora1 and it is not always   
easy to distinguish such cases from the 
fungus-galls 7,mycocecidia7 on the roots
 of ,alders1 ,juncus1 and ,leguminoseae 
where the symbiosis of bacteria or fungi
 with the roots are of benefit to the   
plant4 ,urocystis ,leimbachii forms     
similar nodules at the collar of young  
plants of ,adonis4  ,heterodora javanica
 passes into the cortex of sugar-cane   

roots through fissures1 and makes its   
way to the place where a young rootlet  
is about to emerge2 here it sticks its  
beak into the growing-point and remains 
fixed4  ,molliard has shown that in the 
roots of ,melons1 ,coleus1 etc41        
,heterodora causes the cells in         
immediate contact with its head1 and    
which would normally become vessels of  
the xylem1 to swell up into huge        
giant-cells1 with their walls curiously 
folded1 and containing large supplies of
 proteids and numerous nuclei1 reminding
 us of the food-layer of insect galls   
and of the tapetal layer of pollen-sacs4
 ,while the stimulus exerted by the     
,nematode thus induces hypertrophy and  
storage with food-substances of these   
cells1 those of the next layers undergo 
reticulate thickenings of their walls4  
,again instances of the evolution of new
 tissue elements by the action of the   
foreign organism4  ,so far as galls on  
leaves are concerned the amount and kind
 of damage done are in proportion to the

 area of chlorophyll action put out of  
play for the benefit of the plant1 and  
the remarks already made on p4 #aic     
apply here also4 ,where buds are        
destroyed the effects may of course     
extend further1 but it rarely happens   
that leaf-galls are so abundant as to   
maim a tree permanently4 ,nevertheless  
we must remember that cases like        
,phylloxera are notorious4  ,far more   
dangerous1 however1 are the root-galls  
due to such insects1 because here the   
damage is not so local3 the             
water-supplies are cut off1 and         
injurious consequences result from the  
absorption of the products of           
decomposition in the soil4   ,,notes    
,,to ,,chapter ,,xxiii4       ,in       
addition to the literature on galls     
quoted in the ,notes to      ,chapter   
,,xiv41 the reader should consult ,dale 
,on certain      ,outgrowths            
7,intumescences7 on the green parts of  
,hibiscus1      ,proc4 ,cambr4 ,phil4   
,soc41 ,vol4 ,x41 #ahii1 p4 #aib1 and   

,brit4      ,ass4 ,rep41 ,bradford1     
#aijj4       ,the detailed study of the 
anatomy and histology of ,galls has     
been recently undertaken by ,kuester1   
,beitrage zur ,kenntniss      der       
,gallenanatomie1 ,flora1 ,b4 #hg1 #aijj1
 p4 #aag1 where the      principal      
references will be found4       ,on the 
root-galls due to ,nematodes see        
,atkinson in ,science                   
,contributions from the ,agric4 ,expt4  
,station1 ,alabama1 ,vol4      ,i41 p4  
#a1 #ahhi2 ,percival1 ,an ,eel-worm     
disease of ,hops in      ,natural       
,science1 ,vol4 ,,vi41 #ahie1 p4 #ahg2  
and ,molliard in      ,revue generale de
 ,botanique1 ,apl41 #aijj1 p4 #aeg1     
where the      histology is dealt with4 
,the nodules of the roots of            
,leguminoseae are not part of the       
subject of this work3 the literature is 
collected in ,science      ,progress1   
#ahie1 ,vol4 ,,iii41 p4 #beb1 and       
,dawson1 ,phil4      ,trans41 #aijj4    
,,chapter ,,xxiv4  ,,excrescences       

7continued74                            
,cankers--,burrs--,sphaeroblasts1 and   
other excrescences of      woody        
tissues--,witches' ,brooms4   ,cankers  
are irregular excrescences due to the   
perennial struggle between tissues      
attempting to heal up a wound1 and some 
organism or other agent which keeps the 
lesion open4 ,a canker always originates
 in a wound affecting the cambium1 and  
usually in a small wound such as an     
insect puncture or frost nip2 if        
undisturbed the dead parts would heal   
over by cork and callus1 but if         
recurring frost-cracks break open the   
coverings1 or if insects or fungi       
penetrate the callus and invade the     
cambium1 irregularities of growth due to
 the occluding tissue on the one hand1  
and continued growth of the still       
unimpaired cambium on the opposite side 
of the injured shoot on the other1      
result in the canker4 ,frost cankers    
occur on fruit-trees1 ,vines1 ,beeches1 
etc4  ,cankers due to insects are found 

on ,apples1 the cortex of which is      
punctured by the woolly ,aphis          
7,schizoneura7 while the twigs are      
young1 and the wound is kept open by the
 insects nestling in crevices in the    
occlusion tissues4 ,species of ,coccus1 
,lachnus1 and ,chermes also produce     
cankers on forest trees4  ,cankers due  
to fungi usually originate in a wound   
primarily due to an insect puncture or  
bite1 or to frost1 the invading fungus  
hyphae making their way into the wounded
 tissues and gradually extending more   
and more into the cambium and the       
occluding callus4 ,among the best known 
of these wound fungi which cause cankers
 are ,dasyscypha ,willkommii the peziza 
of ,larch disease1 ,nectria ditissima   
and ,n4 cucurbitula on ,beech and       
,conifers2 less common are ,scleroderris
 on ,willows1 ,aglaospora on ,oaks and  
some others4  ,peridermium ,pini and    
,aecidium elatinum also cause cankers   
under certain conditions1 as also does  
,gymnosporangium1 but in these cases the

 fungi are more truly parasitic4  ,in   
some cases--e4g4 ,ash1 ,pine1           
,olives--bacteria are concerned as      
associated organisms in the cankering of
 trees4  ,burrs or ,knauers are         
irregular excrescences1 principally     
woody1 with gnarled and warted surfaces4
 ,they are frequently due to some       
previous injury1 such as the crushing or
 grazing of cortical tissues by         
cart-wheels4 ,the excitation of the     
tissues thus wounded results in the     
development of shoots from adventitious 
or dormant buds at the base of old tree 
trunks1 or in the starting of the same  
process where a branch has been broken  
off4 ,the new bud begins to develop a   
shoot1 but soon dies at its tip owing to
 paucity of food-supplies to the weak   
shoot1 while new buds at its base repeat
 the process next year with the same    
result1 and each of these again in turn1
 and so on4 ,the consequence is an      
extremely complex nest of buds1 all     
capable of growing in thickness and     

putting on wood to some extent1 but not 
of growing out in length4 ,in course of 
time this mass may attain dimensions    
measurable by feet1 forming huge rounded
 and extremely hard-knotted burrs1 the  
cross-section of which shows the        
vascular tissues running irregularly in 
all directions1 and1 owing to the very  
slow growth1 extremely dense and hard4  
,the dark spots in such sections--e4g4  
,bird's-eye ,maple--are the cut bud-axes
 all fused together1 as it were4 ,on old
 ,elms such burrs are common at heights 
on the stem which preclude the          
assumption of any coarse mechanical     
injury1 and similar structures occur on 
the boles of other forest trees suddenly
 exposed to light by the felling of     
their companions1 which suggests that   
these epicormic shoots result from some 
disturbance due to the action of light4 
,witches' ,brooms are irregular tufts of
 twigs often found among the branches of
 trees such as ,birches1 ,hornbeam1     
etc41 where they look like crows' nests1

 and similar structures are to be found 
on ,silver ,firs and other conifers4 ,in
 the former case they are due to        
,exoascus1 in the latter to ,aecidium1  
fungi which are perennially parasitic in
 the shoots1 and stimulate the twiggy   
development of a number of buds which   
would normally have remained in         
abeyance1 or not have been formed at    
all1 and only do so now in a fashion    
different from that of normal branches4 
,rosette-like formations1 depending on  
similar disturbing causes on the part of
 insects1 occur in conifers--e4g4       
,gastropacha ,pini4  ,dense tufts of    
twiggy shoots may be developed on many  
trees by pruning in such a way as to    
stimulate the shooting out of basal buds
 which would otherwise remain dormant1  
e4g4 ,elm1 ,ash1 and thus it occurs that
 injuries such as frost1 insect bites1  
etc41 may induce the production of such 
tufts in a tree crown4 ,the dense nests 
of stool-shoots thrown up from felled   
tree-stumps are of essentially the same 

nature--partly adventitious and partly  
dormant buds being enabled to grow out  
because they can now be supplied with   
materials previously carried beyond them
 while the trunk was still there4       
,suckers1 if repeatedly cut down1 may   
also behave similarly4  ,wood-nodules or
 ,sphaeroblasts are curious marble-like 
masses of wood which protrude with a    
covering of bark from old trunks of     
,beeches1 etc41 and can be readily dug  
out with a knife4 ,the nodule has arisen
 by the slow growth of the cambium of a 
dormant bud1 the base of which separated
 at an early date from the wood beneath2
 the cambium then closed in over the    
base and laid on thickening rings all   
round the axis of the bud except at the 
extreme apex4 ,when the separation      
occurred the cambium of the wood beneath
 covered over the previous point of     
junction1 and thus the woody bud was    
pushed out with the bark1 and now       
protrudes covered with a thin layer of  
the latter4 ,similar nodules are        

occasionally found on ,apple trees4     
,,notes ,,to ,,chapter ,,xxiv4          
,for further information on ,cankers the
 student should read      ,marshall     
,ward1 ,timber and some of its          
,diseases1 ,chapter ,x4      ,further1  
the discussion as to the causes of      
canker in ,frank1      ,krankheiten der 
,pflanzen1 ,b4 ,i41 p4 #bjg1 and ,b4    
,,iii41 pp4      #afg and #agb1 and     
various papers in ,zeitschrift fuer     
,pflanzen-krankheiten4     ,,chapter    
,,xxv4  ,,exudations ,,and ,,rotting4   
,tumescence--,rankness--,bursting of    
fruits1 etc4--,root rot--,rot      of   
fruits--,bulb                           
diseases--,flux--,honey-dew--,slime     
flux--                                  
,resinosis--,gummosis--,manna4   ,i put 
together in one artificial class a      
varied group of diseases1 the principal 
symptom of which is the escape of fluids
 from the tissues1 under circumstances  
which betray an abnormal state of       
affairs1 often obvious1 but sometimes   

only to be inferred4 ,in many of these  
cases bacteria abound in the putrefying 
mass1 and some evidence exists for      
connecting these microbes causally with 
the disease in a few of the more        
thoroughly investigated cases1 but in no
 case has this been sufficiently        
demonstrated2 and considering the ease  
with which bacteria gain access via     
wounds caused by insects and fungi1 as  
well as by other agents1 the necessity  
for rigid proof must be insisted upon   
before we can accept such alleged       
examples of ,bacteriosis4               
,tumescence4--,it occasionally happens  
that herbaceous parts of plants pass    
into a condition of over-turgescence    
from excess of water in the tissues1 an 
abnormal state which indicates          
pathological changes resulting from     
various causes1 often not evident and   
therefore regarded as internal4 ,such   
disease was formerly termed ,oedema or  
,dropsy4 ,this disease is frequently due
 to the excessive watering of pot plants

 with large root systems and deficient  
foliage1 in hot-houses with a saturated 
atmosphere3 it is1 therefore1 primarily 
referable to diminished transpiration4  
,it can sometimes be brought about by   
covering potato plants1 for instance1   
with a bell-jar in moist1 hot weather2  
and this1 and the prevalence of the     
disease in hot-houses as compared with  
plants grown out of doors1 point to the 
above explanation4 ,similar phenomena do
 occasionally occur out of doors in hot1
 moist situations or during wet seasons1
 however1 and the watery shoots of rank 
vegetation are merely particular cases  
of the same class4 ,moreover1 the       
well-known tendency to succulence of    
sea-side varieties of plants which have 
thin herbaceous leaves when growing     
inland1 points to the action of the     
environment in these matters1 excess of 
salts being no doubt one factor in such 
cases4  ,rankness affords another       
example where superfluity of water is   
concerned1 though it does not involve   

simply this1 because the plant may also 
contain excessive quantities of         
nitrogenous and mineral matters taken up
 by the roots4  ,rankness is1 in fact1  
in many respects analogous to etiolation
 in so far as the tissues are soft and  
surcharged with water1 but it differs   
fundamentally in the deep green of the  
chlorophyll3 this may lead to abundant  
assimilation if free access of air and  
drier conditions can be gradually       
brought about4 ,any sudden drying1      
however1 may be fatal to the tender     
tissues4  ,rankness commonly depends on 
excess of food materials1 especially    
nitrogenous manures1 as may be seen in  
meadows and cornfields where the manure 
heaps have remained on the ground and   
saturated it to excess as compared with 
the rest of the soil2 this may often be 
observed with weeds1 etc41 in the       
neighbourhood of farm-buildings4 ,if the
 period of rank growth is accompanied   
and followed by days of suitably bright 
sunshine and dry air1 the increase of   

vegetative structures usually results in
 increased flowering1 heavy crops1 or   
strong wood2 but if the rankness        
continues too long1 or is accompanied by
 wet and dull weather1 the watery       
tissues are peculiarly susceptible to   
attacks of fungi and insects1 and to    
damage by sudden frosts or chilly winds4
 ,rankness affords1 in fact1 a typical  
illustration of predisposition to       
disease4  ,damping off4--,when seedlings
 are too closely crowded in beds kept   
too damp1 or in moist weather1 they are 
very apt to rot away1 with all the      
symptoms--spreading from a centre1      
contagious infection1 mycelia on and in 
the tissues1 etc4--of a fungus attack4  
,the commonest agent concerned is one of
 the species of ,pythium1 the           
propagation of which is favoured by the 
rank1 over-turgid1 and etiolated        
conditions of the plants4 ,species of   
,mucor1 ,botrytis1 and other fungi1 may 
also be met with4  ,bursting of fleshy  
fruits1 such as ,tomatoes1 ,grapes1     

etc41 is due to over-turgescence in     
rainy weather or excessively moist air4 
,but the phenomenon is by no means      
confined to such organs4 ,hot-house     
plants when oedematous not infrequently 
put out watery blisters from the cortex 
or leaves1 which rupture2 and the stems 
of fleshy fasciated 7e4g4 ,asparagus7 or
 blanched and forced plants 7e4g4       
,celery1 ,rhubarb7 are particularly apt 
to crack here and there from the        
pressure of the turgescent tissues on   
the strained epidermis4 ,beets1         
,turnips1 and other fleshy roots show   
the same phenomena in wet seasons4 ,that
 these ruptures and exposures of watery 
tissues afford dangerous points of entry
 for parasites and moulds will be       
obvious--e4g4 ,edelfaeule1 a rotten     
condition of the grapes in the ,moselle 
district4  ,root-rot is a common disease
 in damp1 sour clay soils after a       
continuance of wet weather--e4g4 ,wheat1
 especially if root-drawn and exposed to
 thaw water4  ,in the disease known as  

,beet-rot1 the roots turn black at the  
tip1 where the tissues shrivel and      
become grooved and wrinkled extensively4
 ,inside the flesh also blackens and    
finally rots4 ,in earlier stages1 only  
the vascular bundles are brown and      
blocked with gum-like substances4 ,in   
advanced stages there is much gummy     
material in the lumina1 and even large  
cavities filled with this gum may be    
found4  ,the rot of ,cherries1 ,pears1  
,apples1 ,plums1 etc41 in store may be  
due to several fungi1 of which          
,botrytis1 ,monilia1 ,mucor1            
,penicillium1 and ,aspergillus are the  
chief4 ,the fruit may be attacked while 
still on the tree1 but very often fungi 
and bacteria gain access to the tissues1
 through bruises1 cracks1 etc41 formed  
in the fruit lying in the storage       
baskets or on the shelves4  ,rot in     
,onions1 ,hyacinth bulbs1 etc41 is      
frequently due to the access of         
,botrytis or ,sclerotinia1 followed by  
moulds1 yeasts1 and bacteria in the     

stores4  ,sour-rot in ,grapes1 and other
 fleshy fruits which need much sun to   
ripen them1 is probably a usual result  
of continued cold1 wet weather at the   
cropping season1 setting in when the    
fruits are beginning to swell4          
,flux4--,it is a common event to see    
fluids of various kinds issuing from    
wounds in trees1 or congealing in more  
or less solid masses about them2 and    
owing to the prevailing tendency to     
compare plant diseases with those of    
animals1 we find such expressions as    
,gangrene1 ,ulcer1 and so forth1 applied
 to these open sores4 ,in so far as such
 outflowings frequently indicate        
diseased states of injured tissues which
 are incapable of healing up1 the       
analogy is perhaps a true one2 but it   
must be remembered that very different  
structures and processes in detail are  
concerned4 ,moreover1 liquid excretions 
more or less indicative of diseased     
states are by no means confined to      
wounds or definitely injured tissues1 in

 which case such terms are wholly       
misapplied4  ,honey-dew4--,the leaves1  
or other organs1 of many plants are     
sticky in hot weather1 owing to the     
excretion of a sweet liquid containing  
sugar1 the consistency and colour of    
which vary according to circumstances4  
,this honey-dew must not be confounded  
with the normal viscidity of certain    
insectivorous plants--e4g4 ,sundew--or  
with the sticky secretion on the        
internodes of species of ,lychnis1 etc41
 where it plays the part of a protection
 against minute creeping things4        
,honey-dew is often met with on ,lime   
trees1 ,roses1 ,hops1 etc4 ,in many of  
these cases the honey-dew is excreted by
 ,aphides1 which suck the juices of the 
leaves and pour out the saccharine      
liquid from their bodies4 ,the sweet    
fluid is in its turn sought after by    
ants1 and also serves as nutritive      
material for various epiphytic          
fungi--e4g4 sooty mould1 ,capnodium1    
,fumago1 and ,antennaria--which give the

 leaves and honey-dew a brown or black  
colour4 ,certain ,coccideae also excrete
 honey-dew1 especially in the tropics4  
,at least one case is known where       
honey-dew is formed as the result of the
 parasitic action of a fungus1 namely   
,claviceps purpurea in its conidial     
stage on the stigmas of cereals1 and    
this may be compared with the sweet     
odorous fluid excreted by the           
spermogonia of certain ,aecidia4 ,in    
both cases the sweet fluid attracts     
insects which disperse the spores4      
,honey-dew may also be formed without   
the agency of fungi or insects1 when hot
 and dry days are followed by cool      
nights1 with a saturated atmosphere1    
e4g4 ,caesalpinia1 ,calliandra and other
 trees in the tropics1 which are called 
rain trees owing to the numerous drops  
of fluid which drip from the leaves     
under the abnormally turgescent         
conditions referred to4                 
,cuckoo-spit4--,the leaves of ,willows1 
,meadow grasses and herbs1 etc41 are    

often seen with froth on them1 in which 
is a green insect1 ,aphrophora1 which   
sucks the juices from the tissues and   
excretes the frothy watery cuckoo-spit  
from its body4  ,slime-flux4--,the      
trunks of trees may sometimes be        
observed to pour out a slimy fluid from 
cracks in the bark1 or from old wounds1 
or branch scars4 ,in some cases1 e4g4 in
 ,oaks1 the slime has a beery odour and 
white colour1 and abounds in yeasts and 
other fungi to the fermentative activity
 of which the odour and frothiness are  
due4 ,in other cases the slime is red   
e4g4--,hornbeam2 or brown--e4g4 ,apple  
and ,elm2 or black--e4g4 ,beech1 the    
colour in such cases being due to the   
mixture of yeasts1 bacteria1 and fungi  
with which these slimes abound4 ,the    
phenomenon appears to be due to the     
exudation of large quantities of sap    
under pressure--root pressure--and is   
primarily a normal phenomenon comparable
 to the bleeding of cut trees in spring3
 the fungi1 etc41 are doubtless         

saprophytes1 but their activity is      
concerned with the putrefactive         
processes going on in the diseased wood1
 and which may lead to rotting of the   
timber4  ,the origin of the wounds in   
the bark and cortex1 and which extend   
into the wood and other tissues as the  
putrefactive and fermentative processes 
increase1 appears to be in some cases at
 least due to lightning4  ,resin-flux or
 ,resinosis4--,the stems of ,pines and  
other conifers are apt to exude resin   
from any cut or wound made by insects1  
or by the gnawing of other animals2 but 
in many cases the flow is due to fungi1 
e4g4 ,peridermium1 the hyphae of which  
invade the medullary rays and resin     
canals and thus open the way to an      
outflow through cracks in the bark4     
,agaricus melleus not only invades the  
resin passages1 but stimulates the tree 
to produce abnormal quantities of resin1
 which flows down to the collar and     
roots1 and exudes in great abundance at 
the surface of the soil4 ,various other 

plants also exude resin from wounds1 and
 in some cases the flux seems to be     
increased by degeneration of the        
tissues1 e4g4 ,copaifera4               
,gummosis4--,cherries1 ,apricots1       
,acacias1 and many other trees are apt  
to produce abnormal quantities of gum1  
which flows from any wound or exudes    
through cracks in the bark4             
,degeneration of the wood-cells1 and    
especially of the cell-walls of a soft  
wood formed by abnormal activity of the 
cambium1 points to its origin being due1
 in some cases at any rate1 to a        
conversion of the cellulose1 and fungi  
are sometimes found in the masses of    
gum2 but beyond the fact that gummosis  
is a pathological phenomenon we know    
very little of the disease4  ,with      
regard to such gumming1 it is           
significant how frequently pruned       
trees--,cherries1 ,oranges1 ,lemons1    
,plums1 etc4--suffer4  ,manna           
flux4--,certain trees1 such as the      
,manna ,ash1 species of ,tamarisk1 etc41

 yield manna from wounds1 and in some   
cases the latter are due to insects1    
e4g4 ,cicada4  ,the ,potato-disease is  
best known by the pale whitish fringe1  
giving an almost mealy appearance to the
 margins of the brown to black patches  
in damp weather4 ,in dry weather the    
brown patches shrivel and dry1 and as   
they are apt to be at the edges and tips
 of the leaflets1 these curl up4 ,the   
young disease spots are yellowish1 and  
the leaves of badly affected plants are 
apt to be sickly yellow throughout4     
,this ,potato-disease due to            
,phytophthora must be distinguished from
 the curling and puckering1 with wilting
 and browning of the leaves and yellow  
glassy look of the stems1 due to the    
invasion of the vessels by a fungus     
which lurks in the tubers1 and gains    
access thence to the shoots4  ,in the   
disease traceable to ,phytophthora the  
stock remains green and the leaves plump
 and plane1 and only the brown patches  
slough out in wet or shrivel in dry     

weather1 and are bordered by the pale   
whitish zone of conidiophores4  ,in the 
leaf-curl the yellow and flaccid        
appearance of all the leaves of a stalk1
 or even of the plant1 is the striking  
symptom1 and the stem soon droops and   
blackens just above the soil1 a white   
mould appearing also at the black spots4
 ,subsequently black spots appear higher
 up1 and bacteria gain an entrance4 ,the
 stolons rot1 and eventually the roots  
and the leaves wither4 ,the tubers      
appear sound1 but are small2 they are   
apt to rot in the store1 the vascular   
zones turning brown4  ,this leaf-curl   
has been ascribed to ,pleospora1        
,polydesmus1 ,verticillium1 and other   
parasites1 as well as to excessive      
manuring and other agencies1 but it     
still needs explanation4  ,rot of       
,potato tubers in the soil1 or in store1
 may be brought about by very different 
agents4  ,if ,phytophthora has obtained 
access1 the fungus hyphae spread between
 the cells1 starting from the haulm1 and

 cause the flesh to turn yellowish and  
then brown in patches4 ,on the exterior 
are discoloured patches1 depressed1 with
 the flesh beneath brown and soft4 ,the 
mycelium spreads mostly in the outer    
layers1 which though they turn deep     
brown remain firm4  ,wet rot of potatoes
 may be due to various fungi1 and1 in   
excess of water1 to putrefactive        
bacteria 7e4g4 ,clostridium71 which     
destroy the cell-walls4 ,the flesh      
becomes soft1 then soup-like1 and       
finally putrefies to a liquid mass with 
a vile smell of butyric acid1 etc41 in  
which the starch grains may be seen     
floating4  ,tubers are often found with 
the cork burst and peeling in shreds1   
the flesh more or less converted into a 
putrid and stinking pulp1 with a spotted
 brown boundary of partly destroyed but 
firmer tissue between the dark utterly  
rotten and the white and still firm     
healthy flesh4 ,the principal agent in  
the destruction of the tissues is       
,clostridium1 an anaerobic bacillus     

which consumes the cell-walls but leaves
 the starch intact4 ,hence a thoroughly 
decomposed tuber consists of a cork bag 
full of starch and foetid liquid4 ,in   
the dried condition the flesh shows a   
brown marbling2 this passes into a soft 
soupy starchy part1 and here and there  
may be violet grey cavities lined with  
,spicaria1 ,hypomyces1 etc41 the white  
stromata of the latter often appearing  
externally4 ,the excavations are filled 
with loose starch grains1 and bounded by
 cork and cambium formed in the         
peripheral cells4 ,the cell-walls       
eventually undergo slimy decomposition4 
,spicaria1 ,fusisporium1 various moulds1
 and bacteria may all be associated with
 wet-rot4  ,dry-rot of ,potatoes is also
 due to various fungi and bacteria1 but 
the destructive action goes on slowly1  
owing to there being no more moisture   
than the tissues afford4 ,the flesh     
becomes excavated here and there1 owing 
to the slow destruction of the          
cell-walls by ,clostridium3 the         

destroyed tissues are brown1 and the    
uninjured starch grains powder them all 
over4 ,finally the whole shrunken mass  
has a crumbly consistency4  ,when the   
flesh remains white1 but assumes a      
powdery consistency and dry-rot1 with   
the cork destroyed here and there1      
,frank refers the damage to             
,phellomyces4 ,where the dry-rot is due 
to ,fusarium the chalk-white stromata   
may often be detected breaking through  
the periderm2 but it must be remembered 
that the soil-contaminated1 broken skin 
of a potato-tuber is a favourable       
lurking spot for many fungi1 and        
,periola1 ,acrostalagmus1 and others    
have been detected therein4  ,brown     
spots1 depressed into the flesh1        
sometimes result from the ravages of    
,tylenchus1 the minute worms being found
 in the diseased tissues4  ,in some     
cases the flesh turns watery and soft1  
grey1 almost glass-like1 starting at the
 haulm end1 and this may be owing to the
 invasion of ,rhizoctonia4   ,,notes    

,,to ,,chapter ,,xxv4       ,the rotting
 of bulbs1 roots1 etc41 has been much   
discussed      during the last few years
 in the pages of the ,gardeners'        
,chronicle1 ,zeitschrift fuer           
,pflanzenkh41 and elsewhere4 ,the       
principal references to                 
,bacteriosis--the rot in which bacteria 
are stated to be the primary agent      
causing these and similar               
diseases--may be found in ,massee1      
,diseases of ,plants1 pp4      #cch-cdb1
 and more fully in ,russell1 ,bacteria  
in their      ,relation to ,vegetable   
,tissue1 ,baltimore1 #ahib2 and in      
,migula1      ,kritische ,uebersicht    
derjenigen ,pflanzen-krankheiten1 welche
      ,angeblich durch ,bakterien       
verursacht werden1 ,semarang1 #ahib4    
,the most convincing accounts1 however1 
are since that date2      see ,smith1   
,pseudomonas ,campestris1 ,cent4 f4     
,bakt41 ,b4      ,,iii41 #ahig1 p4 #bhd1
 and ,arthur and ,bolley1 ,bacteriosis  
of      ,carnations1 ,perdue ,university

 ,agr4 ,expt4 ,station1 #ahif1 ,vol4    
,,vii41 p4 #ag4 ,woods has lately shown 
that this disease is due      to        
,aphides only1 the bacteria having      
nothing to do with the      disease     
primarily1 ,stigmonose1 ,bull4 #ai1     
,u4,s4 ,dept4 ,agr41      #aijj2 but it 
is necessary to bear in mind that actual
      penetration of the cell-walls from
 without must be proved1 as      ,de    
,bary proved it for germ-tubes of fungi1
 before the evidence      that ,bacteria
 are truly parasitic in living plants   
can be      called decisive4 ,this is a 
difficult matter1 but until it is       
settled we do not know whether these    
organisms are really      parasitic in  
the sense that ,phytophthora is1 or     
merely gain      access by other        
means--,i have traced them through dead 
fungus-hyphae--to the vessels1 dead     
cell-walls1 etc4 ,the proof      of     
infection via water pores and vessels is
 given for one      species by ,harding1
 ,die ,schwarze ,faulnis der ,kohls1    

etc41      ,cent4 f4 ,bakt41 ,abh4      
,,ii41 ,b4 ,,vi41 #aijj1 p4 #cje1 with  
literature4       ,concerning the       
,damping off of seedlings1 see ,marshall
 ,ward1      ,observations on the ,genus
 ,pythium1 ,quart4 ,journ4 ,microsc4    
,soc41 ,vol4 ,,xxiii41 #ahhc1 p4 #dhe1  
and ,atkinson1 ,bull4 #id of            
,cornell ,university ,agric4 ,expt4     
,station1 #ahie1 p4 #bcc4       ,on     
,bacteriosis in ,turnips1 see ,potter1  
,proc4 ,r4 ,s4 #aija1      ,vol4        
,,lxvii41 p4 #ddb4     ,,chapter ,,xxvi4
  ,,necrotic ,,diseases4                
,patches--,frost-patches--,bruising due 
to hail1 shot1 etc4--                   
,fire--,sun-burn or                     
scorching--,sun-cracks4                 
,dying-back--,frost--                   
,fungi--,wound fungi--,defoliation by   
insects--,defoliation by                
hand--,staghead4   ,necrosis4--,this is 
a general term for cases where the      
tissues gradually turn brown or black in
 patches which die and dry up1 the dead 

area sometimes spreading slowly and     
invading the usually sharply demarcated 
healthy tissues around4 ,it is a common 
phenomenon on the more slender stems or 
branches of trees1 especially those with
 a thin cortex1 and the terms ,brand or 
,scorching sometimes applied signify the
 recognised resemblance between burnt   
patches and these dead areas of necrotic
 tissue4  ,necrosis is often due to     
frost1 which kills the cortex of ,pears1
 ,beech1 etc41 in patches of this kind4 
,the dead cortex and cambium stick to   
the wood beneath and contract as they   
dry4 ,the living cambium and cortex     
around them then begin to push in callus
 towards the centre of the necrotic     
area2 but since this callus is formed   
under the pressure of the cortical      
tissues it does not form a thick lip or 
margin to the healing wound1 as it does 
in a ,canker1 but insinuates itself with
 thinned-off edges between the wood and 
the dead tissue1 or at most traps a     
little of the latter in the final       

closing up of the wound4 ,it is easy to 
see how such an area of ,necrosis may   
become a ,canker if the dead tissues    
split or slough off1 and fungi or       
insects obtain access to the callus at  
the margins of the area1 setting up the 
disturbances described on p4 #bbb4 ,as  
matter of fact many ,cankers--e4g4 those
 of the ,larch disease1 and those due to
 ,nectria1 or ,aphides1 etc4--often     
begin as flattened or depressed areas of
 ,necrosis started by frost1 and many   
small necrotic patches would eventually 
become ,cankers if not healed up by the 
callus4  ,necrosis may also be due to   
the bruising of the tissues by large    
hailstones1 to gun-shot wounds1 or to   
any form of contusion which kills the   
living cells of cortex and cambium4     
,necrosis is a natural and common result
 of fire1 and it frequently happens     
after forest-fires which have run       
rapidly through the dry underwood1      
fanned by steady winds1 that the lower  
parts of the boles are scorched on one  

side only4 ,the killed cambium and      
cortex then dry up in black necrotic    
patches1 which may eventually heal up by
 intrusion of callus from the uninjured 
parts4  ,sun-burn or ,scorching4--,if   
thin-barked trees1 such as ,hornbeam1   
,beech1 ,firs1 etc41 which have been    
growing in partial shade owing to dense 
planting1 are suddenly isolated by      
thinning1 the impingement of the sun's  
rays on the south-west side during the  
hottest part of summer days may kill the
 cambium1 and produce necrosis of the   
cortical tissues1 and such necrotic     
patches heal very slowly or not at all1 
because the dead tissues have contracted
 so tightly on to the wood below that   
the callus cannot readily creep between4
  ,sun-cracks are due to intense        
insolation on the south side of trees in
 clear weather in early spring1 causing 
the drying and contraction of the wood  
and its coverings down that side of the 
tree3 the contracted tissues            
consequently split1 as in the case of   

frost-cracks1 the healing up of which is
 very similar4  ,dying-back4--,all that 
is true of the necrosis of cortical     
tissues in small patches also applies to
 cases where the whole of the outer     
tissues of thin twigs and branches die  
of inanition owing to a premature fall  
of leaves--e4g4 after a severe attack of
 some insect or fungus pest4 ,the       
consequent arrest of the transpiration  
current and the proper supply of        
nutriment to the cambium and cortex     
explain the phenomena4 ,the younger     
branches of ,coffee trees suffering from
 severe attacks of leaf-disease are     
often denuded of leaves and die back    
from the causes mentioned1 the whole of 
the outer tissues becoming necrotic1 and
 drying up tight on to the wood1 because
 other branches with functionally active
 leaves on them divert the transpiration
 current1 and drought and inanition     
supervene4  ,dying-back is frequently   
also a direct effect of early frosts1   
which kill the thin twigs before the    

wood is ripened1 as gardeners say4      
,dying-back is also a frequent result of
 direct frost action on thin watery     
shoots or unripe wood1 and is apt to    
occur every year in certain varieties of
 ,roses1 for instance1 in particular    
situations1 such as frost-beds1 or      
aspects exposed to cutting winds1 and so
 forth4 ,the necrosis which results may 
affect all the tissues1 or only the     
cortex and cambium1 and the frequent    
accompaniment of all kinds of           
saprophytic ,ascomycetes and moulds or  
other fungi is in no way causal to the  
phenomenon4  ,dying-back may also be    
caused by fungi1 and not necessarily    
parasites1 for cases are often observed 
where saprophytes only are to be found  
in the necrotic tissues of the cortex1  
having made their way in through minute 
cracks1 lenticels1 etc4  ,a simple case 
is often seen in ,chrysanthemums1       
,roses1 etc41 chilled and wetted to     
danger point1 but not frozen1 during the
 nights of autumn4 ,the lowered         

resistance of the chilled tissues       
enables fungi like ,botrytis cinerea to 
gain a hold1 and the peduncles die-back 
with all the symptoms of ,necrosis1 the 
fungus gaining power more and more as   
its mycelium spreads in the dead        
tissues4  ,many other cases are known   
where wound-fungi1 such as ,nectria1    
,cucurbitaria1 ,phoma1 etc41 in         
themselves incapable of true parasitism1
 gain a hold on the necrotic tissue of a
 wounded twig1 and having laboriously   
accumulated a vigorous mycelium         
saprophytically1 extend into other      
parts4 ,in many of these cases the      
dying-back of the twigs is expedited    
owing to the mycelium invading the      
medullary rays and wood vessels1 and so 
obstructing the transpiration current4  
,the much more rapid spread of the      
hyphae up into the parts thus killed    
sufficiently indicates the fundamentally
 saprophytic character of such fungi4   
,dying-back in all its forms is a common
 result of defoliation by insects1 e4g4 

caterpillars1 especially if it occurs   
when the wood is depleted of reserve    
materials1 and thus cannot supply the   
auxiliary buds and enable the twigs to  
clothe themselves with a new flush of   
foliage1 a common danger in ,conifers4  
,any form of defoliation--e4g4 excessive
 plucking of tea and mulberry leaves1   
browsing of animals1 etc4--exposes the  
twigs to the dangers of dying-back1 the 
accessory phenomena being similar to    
those already described4                
,stag-head4--,old trees1 though vigorous
 and in full foliage throughout the     
crown generally1 frequently lose the    
power of bearing leaves on their topmost
 branches and twigs1 which stand out    
bare and brown1 and fancifully resemble 
the antlers of a stag3 hence the        
forester's name stag-head4 ,this top-dry
 condition is frequently due to the     
removal of litter1 or to excessive      
draining1 or to the roots having        
gradually penetrated into unsuitable    
soil4 ,the consequence is that some dry 

summer the drought causes the breakage  
of the water columns above1 and the     
twigs die back4  ,tropical trees may    
also become stag-headed owing to the    
attacks of ,loranthus and other         
parasites1 the portions above the point 
of attachment dying back from inanition4
  ,cases also occur in the tropics where
 the stag-head condition is due to the  
persistent roosting of frugiferous      
bats--flying foxes--which tear the bark 
and foliage with their claws1 and befoul
 the twigs generally4   ,,notes ,,to    
,,chapter ,,xxvi4       ,the principal  
literature as regards frost is given in 
the      works of ,frank1 ,sorauer1 and 
,hartig already referred to4 ,an        
excellent summary will be found in      
,hartig's ,diseases of      ,trees1 p4  
#bhb1 and in ,fisher ,forest            
,protection1 ,vol4 ,,iv4 or             
,schlich's ,manual1 p4 #dbc4            
,,chapter ,,xxvii4  ,,monstrosities     
,,and ,,malformations4                  
,monstrosities--,teratology--,atrophy of

 organs--,shanking of                   
grapes--,barren fruit                   
trees--,dwarfing--,distortions and      
malformations--,fasciations--,flattened 
roots--,torsions--,curling      and     
puckering--,leaf rolling--,so-called    
spontaneous      teratological changes4 
,monstrosities4--,in a wide sense this  
term is applicable to many cases here   
treated under other headings1 and       
signifies any departure from the normal 
standard of size1 form1 arrangement1 or 
number of parts1 and so forth1 due to   
arrest of growth1 excessive growth of   
parts1 or of the whole organs1 etc4     
,such teratological conditions are      
however by no means always pathological3
 that is to say1 they may be variations 
which do not threaten the existence of  
the plant4 ,in some cases they are      
clearly due to exuberant nutrition1 and 
although they may occasionally          
predispose to disease1 in others they   
show no evidence of doing so4 ,the whole
 practice of horticulture and           

agriculture abounds in examples of      
teratological sports or varieties which 
are transmissible by seeds1 budding and 
grafting1 and other means--e4g4 double  
flowers1 hypertrophied floral organs    
7cauliflowers71 seedless grapes and     
oranges1 crested ferns1 etc42 and even  
when such varieties could not live as   
such in a state of nature1 there is     
evidence to show that many of them      
readily revert to the original          
seed-bearing or single condition1 and   
adapt themselves to the altered         
environment4  ,every part of the plant  
may exhibit teratological changes1 and  
,i shall for the most part select cases 
in illustration which indicate approach 
to pathological states1 and group with  
them cases known to be pathological in  
origin4  ,atrophy is a common phenomenon
 denoting dwindling or reductions in    
size of organs due to insufficient      
nutrition1 or arrest of growth from     
various causes4  ,atrophy of leaves is a
 common result of the attacks of        

parasitic fungi1 even when the latter   
induce local hypertrophy--i4e4 excessive
 growth of particular parts1 e4g4       
,synchytrium on ,dandelions and         
,anemones4 ,puccinia suaveolens causes  
partial atrophy of the leaves of        
,thistles1 ,aecidium ,euphorbiae of     
those of ,euphorbia4  ,the carpels of   
,anemone are atrophied in plants        
attacked by ,aecidium1 and the whole    
flower is suppressed in ,cherries       
infested with ,exoascus ,cerasi1 while  
other fungi--e4g4 ,cystopus1 ,exoasci1  
etc4--cause atrophy of the seeds1 and   
numerous instances of atrophied grain   
occur in plants infested with           
,ustilagineae4  ,atrophy of the grains  
of cereals is sometimes due to the      
direct attack of animals1 e4g4 eel-worms
 7,tylenchus7 eat out the grains of     
,corn2 weevils and other beetles        
7,curculio1 ,bruchus1 etc47 similarly   
devour the contents of grain and nuts1  
the flowers of ,peas and ,apples1 and so
 forth1 inducing atrophy of the parts   

left4 ,still more striking cases are    
afforded by small insects which bore    
into the halms of cereals1 and cause    
atrophy of the whole ear--e4g4 ,cephus  
in ,wheat and ,rye4 ,barley occasionally
 withers after flowering1 the grain     
atrophying from no known cause1 terms   
like consumption given to the disease   
conveying no information4  ,atrophy of  
young fruits is commonly due to the     
flowers not setting--i4e4 some agent has
 interfered with the normal transference
 of the pollen to the stigma4 ,this may 
be due to excessive rain washing out the
 pollen 7e4g4 ,vine71 to a lack of the  
necessary insects which effect          
pollination1 often seen in greenhouse   
plants2 to the stamens being            
barren--e4g4 certain varieties of       
,vine--or to the premature destruction  
of the stigmas by frost1 as in          
,cherries1 ,pears1 etc41 or by insects1 
as in ,apples1 or fungi1 e4g4 the       
infection of bilberries with            
,sclerotinia2 or even by poisonous      

gases1 as is sometimes seen in ,wheat1  
etc41 growing near alkali works4        
,drought is also a common cause of      
atrophy of young ,plums4  ,shanking of  
,grapes is a particular case of atrophy 
and drooping of the immature fruits1 due
 to the supplies being cut off by some  
agency4 ,it may arise from very various 
causes which bring about disease in the 
leaves or roots1 and should always be   
looked upon as a sign of weakness in the
 ,vine1 the structure of which is       
affected1 e4g4 poor wood--or the        
functions interfered with1 e4g4 water   
supplies deficient owing to paucity of  
roots4  ,barren ,apple1 ,pear1 ,plum1   
and other flowers are often found to    
have been bored through the petals while
 in bud1 and the whole heart of the     
flower eaten out by the grubs of        
,anthonomus1 leaving the unopened buds  
brown and dead1 as if killed by frost or
 drought1 and often erroneously supposed
 to be so4  ,the wilting and shrivelling
 of ,clover is sometimes due to         

,sclerotinia1 the mycelium of which     
pervades the roots and stock1 on which  
the sclerotia may be found4 ,lucerne is 
similarly killed in ,europe by the      
barren mycelium of ,leptosphaeria1 which
 may be found as a purple mat on the    
roots4  ,dwarfing consists in partial   
atrophy of all the organs1 and is a     
common result of starvation in poor1    
dry1 shallow soils1 as may often be seen
 in the case of weeds on walls or in    
stony places4 ,dwarfs which are thus    
developed in consequence of perennial   
drought are not1 however1 necessarily   
diseased1 in the more specific sense of 
the word2 their organs are reduced in   
size proportionally throughout in       
adaptation to the conditions1 and simply
 carry out their functions on a smaller 
scale4  ,dwarfing is frequently a       
consequence of the lack of food         
materials1 or of some particular        
ingredient in the soil1 and in such     
cases is a diseased condition of some   
danger2 similar results may ensue in    

soils containing the necessary chemical 
elements1 but in unavailable forms4     
,dwarfing may also be brought about by  
repeated maiming1 nipping off the buds1 
pruning1 etc41 as in the miniature trees
 of the ,japanese2 and the case of trees
 continually browsed down by cattle1 or 
of moor plants perennially dwarfed by   
cutting winds1 are further illustrations
 in the same category1 as are also those
 of certain alpine and moraine plants1  
whose only chance of survival depends on
 their adapting themselves to the       
repeated prunings suffered by every     
young shoot which rises into the cutting
 winds1 since there is no question of   
lack of food-materials in these cases4  
,the practice of the ,japanese is to    
pinch out the growing tips of the shoots
 wherever they wish to prune back1 and  
it is by the judicious use of this      
heading in1 and suitable pot-culture1   
that the dwarfs are made1 #f-bj inches  
high at from #cj-hj years old4          
,dwarfing is often brought about by     

grafting on a slow-growing stock1 and   
this method is employed in practice1 as 
are also heading in1 pruning of roots1  
and confinement in pots4  ,dwarfing may 
also be due to poor or                  
shrivelled--partially atrophied--seeds  
or such as have had their endosperms or 
embryos injured by insects or fungi1 and
 although it is possible to nurse such  
dwarfs into normal and vigorous plants  
with good culture1 they do not usually  
recover under natural conditions in     
competition with more vigorous plants4  
,distortions or ,malformations may be   
defined as abnormalities in the form of 
organs which concern all1 or nearly all 
the parts1 and do not refer merely to   
swellings or excrescences on them or    
excavations1 etc41 in them4             
,fasciation4--,shoots of ,asparagus1    
,pine1 ,ash1 and many other plants are  
occasionally expanded into broad        
ribbon-like structures often studded    
with more than the normal number of buds
 or leaves1 etc41 such as would be found

 on the usual cylindrical shoots4 ,such 
fasciations are due to several buds     
fusing laterally under compression when 
young and the whole mass growing up in  
common1 or1 in a few cases1 to the      
unilateral overgrowth of one side of the
 terminal bud4 ,fasciations appear to   
depend on excessive nutrition in rich   
soils4 ,they may spread out above in a  
fan-like manner1 exaggerating the       
abnormality1 or they may revert to the  
original form4 ,some cases are more or  
less fixed by heredity--e4g4 ,celosia4  
,fasciated stems are frequently curved  
like a crozier1 owing to one edge       
growing more rapidly than the other4    
,cauliflowers are really cultivated     
monstrosities4 ,fasciated ,dandelions1  
,crepis1 monstrous ,chrysanthemums1     
peloric ,linaria1 five-leaved ,clovers1 
spiral ,teazels1 etc41 may all1 if grown
 with care1 be kept more or less        
constant in the monstrous state4 ,that  
is to say1 the particular kinds of      
variation here manifested can be        

maintained in proportion as the external
 conditions controlling the variation   
are maintained4 ,such conditions are    
chiefly rich supplies of food-stuffs1   
plenty of water and air1 suitable       
temperature and lighting1 etc4          
,mutilations1 favouring the development 
of abnormal buds may also induce        
fasciations4  ,torsions or spiral       
twistings of stems also frequently arise
 among plants grown in rich soils1 and  
are often combined with                 
fasciations--e4g4 ,asparagus1 ,dipsacus2
 and ,de ,vries has shown that the      
peculiarity is not only transmissible by
 seed1 but may be more or less fixed by 
appropriate culture4  ,contortions of   
stems are often due to the unequal      
growth on different sides of the stems  
owing to the presence of fungi--e4g4    
,caeoma on ,pines1 ,aecidium on         
,nettles1 also ,puccinia on petioles of 
,mallow1 ,cystopus on inflorescences of 
,capsella1 etc4  ,distortions of roots  
may be brought about in various ways by 

the hindrances afforded by stones4      
,spiral roots occur occasionally in pot 
plants4  ,flattened roots usually result
 from compression between rocks1 the    
young root having penetrated into a     
crevice1 and been compelled to adapt    
itself later4 ,the distortions of stems 
by constricting climbers1 wire1 etc41   
have been described1 and fruits--e4g4   
,gourds--are easily distorted by means  
of string tied round them when young4   
,distortions of leaves are very common1 
and are sometimes teratological--i4e4   
due to no known cause--e4g4 the         
pitcher-like or hood-like cucullate     
leaves of the ,lime1 ,cabbage1          
,pelargonium1 etc41 and of fused pairs  
in ,crassula4 ,also coherent1 bifurcate1
 crested1 displaced and twisted leaves  
occasionally met with1 and in some cases
 fixed by cultivation1 may be placed in 
this category4  ,puckers must be        
distinguished from pustules1 since they 
consist in local upraisings of the whole
 tissue1 not swellings--e4g4 the        

yellowish green pockets on ,walnut      
leaves1 due to ,phyllereum4  ,puckered  
leaves in which the area of mesophyll   
between the venation is increased by    
rising up in an arched or dome-like     
manner are sometimes brought about by   
excessive moisture in a confined space4 
,leaf-curl is a similar deformation     
caused by fungi1 such as ,exoascus on   
,peaches4  ,wrinkling or puckering of   
leaves is also a common symptom of the  
work of ,aphides--e4g4 ,hops4           
,characteristic curling and puckering1  
with yellow and orange tints1 of the    
terminal leaves of ,apples1 ,pears1     
etc41 are due to insects of the genera  
,aphis1 ,psylla1 etc4  ,small red and   
yellow spots with puckerings and        
curlings of the young leaves of ,pears1 
the spots turning darker later on1 are  
due to ,phytoptus4  ,leaf-rolling4--,the
 leaves of ,beeches1 ,poplars1 ,limes1  
and many other plants1 instead of       
opening out flat1 are often rolled in   
from the margins1 or from the apex1 by  

various species of ,phytoptus1          
,cecidomyia1 or other insects1 which    
puncture or irritate the epidermis in   
the young stages and so arrest its      
expansion in proportion to the other    
tissues4 ,according as the lower or     
upper surface is attacked the rolling is
 from the morphologically upper surface 
downwards1 or vice versa4 ,very often   
the mesophyll is somewhat thickened     
where rolled and ,erineum-like hairs may
 be developed--e4g4 ,lime4 ,many        
caterpillars also roll leaves1 drawing  
the margins inward to form              
shelters--e4g4 ,tortrix viridana1 the   
,oak leaf-roller4 ,certain              
beetles--,rhynchitis--also roll up      
several leaves to form a shelter in     
which the eggs are laid4  ,webs are     
formed among the mutilated leaves of    
,apples by the caterpillars of          
,hyponomeuta4  ,it must be borne in mind
 that instances can be found of         
teratological change of every organ in  
the plant--e4g4 stamens transformed into

 carpels or into petals2 anthers partly 
polliniferous and partly ovuliferous2   
ovules producing pollen in their        
interior1 and so on1 being simply a few 
startling examples of what may happen4  
,such abnormalities are frequently      
regarded as evidence of internal causes 
of disease1 and this may be true in     
given cases2 in a number of cases       
investigated1 however1 it has been shown
 that external agents of very definite  
nature bring about just such            
deformations as those sometimes cited as
 examples of teratology due to internal 
causes1 and the question is at least an 
open one whether many other cases will  
not also fall into this category4 ,the  
study of galls has shown that insects   
can induce the formation of not only    
very extraordinary outgrowths of tissues
 and organs already in existence1 but   
even of new formations and of tissue    
elements not found elsewhere in the     
plant or even in its allies2 and ,solms'
 investigations on ,ustilago ,treubii   

show that fungi can do the same1 and    
even compel new tissues1 which the      
stimulating effects of the hyphae have  
driven the plant to develop1 to take    
part in raising and distributing the    
spores of the fungus--i4e4 to assume    
functions for the benefit of the        
parasite4 ,molliard has given instances 
of mites whose irritating presence in   
flowers causes them to undergo          
teratological deformations1 and         
,peyritsch has shown that the presence  
of mites in flowers induces             
transformations of petals into sepals1  
stamens into petals4 ,similarly ,de     
,bary1 ,molliard1 ,magnus1 ,mangin1 and 
,giard have given numerous cases of the 
transformation of floral organs one into
 another under the irritating action of 
fungi1 of which the transformation of   
normally unisexual 7female7 flowers into
 hermaphrodite ones1 by the production  
of stamens not otherwise found there1   
are among the most remarkable4  ,these  
and similar examples suffice to awaken  

doubts as to whether any teratological  
change really arises spontaneously1     
especially when we learn how slight a   
mechanical irritation of the growing    
point may induce changes in the flower2 
e4g4 ,sachs showed that a sunflower head
 is profoundly altered by pricking the  
centre of the torus1 and ,molliard got  
double flowers by mechanical irritation4
   ,,notes ,,to ,,chapter ,,xxvii4      
,for the details and classification of  
the multitude of facts1      the student
 is referred to ,masters' ,vegetable    
,teratology1      ,ray ,society1 #ahfi1 
and the pages of the ,gardeners'        
,chronicle      since that date4        
,concerning torsions1 etc41 the student 
should read ,de ,vries1      ,on        
,biastrepsis in its ,relation to        
,cultivation1 ,ann4 of      ,bot41 ,vol4
 ,,xiii41 #ahii1 p4 #cie1 and           
,hybridising of      ,monstrosities1    
,hybrid ,conference ,report1 ,roy4      
,hort4 ,soc41      #aijj1 ,vol4 ,,xxiv41
 p4 #fi4       ,the reader will find an 

excellent account of the abnormalities  
in flowers due to the action of         
parasitic insects and fungi in          
,molliard1 ,cecidies ,florales1 ,ann4   
des ,sc4 ,nat41 ,ser4      ,,viii41     
,bot41 ,t4 #a1 #ahie1 p4 #fg4           
,,chapter ,,xxviii4  ,,proliferations4  
,proliferations--,vivipary--,prolepsis--
,lammas shoots--,dormant                
buds--,epicormic shoots--,adventitious  
buds--,apospory and      apogamy4       
,proliferation consists in the          
unexpected and abnormal on-growing or   
budding out of parts--stems1 tubers1    
flowers1 fruits1 etc4--which in the     
ordinary course of events would have    
ceased to grow further or to bear buds  
or leaf-tufts directly4 ,thus we do not 
expect a ,strawberry--the swollen floral
 axis--to bear a tuft of leaves         
terminally above the achenes1 but it    
occasionally does so1 and similarly     
,pears may be found with a terminal tuft
 of leaves1 ,roses with the centre      
growing out as a shoot1 ,plantains      

7,plantago7 with panicles in place of   
simple spikes1 and so on4  ,we regard   
such cases as teratological1 because    
they are exceptional for the particular 
species1 and as pathological because    
they appear to be connected with        
over-feeding in soils with excessive    
supplies of available food-materials2   
but it should be noted that conditions  
quite comparable to proliferation are   
normal in the inflorescences of         
,pine-apples1 some ,myrtaceae1          
,conifers1 etc41 and that many instances
 of proliferations come under the head  
of injurious actions of fungi1 insects1 
and other agents4  ,proliferation of    
tubers is sometimes seen in ,potatoes   
still attached to the parent plant in   
wet weather following a drought4 ,the   
eyes grow out into thin stolons1 or     
forthwith into new tubers sessile on the
 old tuber4 ,similarly in store we      
sometimes find the eyes transformed     
directly into new tubers1 and cases     
occur where the growth of the eye is    

directed backwards into the softening   
tuber1 and a small potato is formed     
inside the parent one4  ,threading is   
also occasionally met with in the sets  
when ripened too rapidly in hot dry     
soils4  ,vivipary is a particular case  
of proliferation1 in a certain sense1   
where the seeds appear to germinate in  
situ1 and we have small plants springing
 from the flowers1 reminding us of wheat
 which has sprouted in the shocks in    
damp weather4 ,in reality1 however1 the 
grains are here replaced by bulbils     
which sprout before they separate from  
the inflorescence4 ,in varieties of     
,poa1 ,polygonum1 ,allium1 ,gagea1 etc41
 this phenomenon is constant in plants  
growing in damp situations4             
,prolepsis4--,it frequently happens that
 branches or whole plants are suddenly  
defoliated in summer1--e4g4 by          
caterpillars or other insects--at a time
 when considerable stores of reserves   
had already been accumulated during the 
period of active assimilation4 ,in such 

cases the axillary buds1 which would    
normally have passed into a dormant     
condition over the winter had the leaves
 lived till the autumn-fall1 suddenly   
shoot out into proleptic shoots 7also   
termed ,lammas shoots71 and reclothe the
 tree with foliage4 ,the wood of the    
year in which this occurs may exhibit a 
double annual ring1 and the vigour of   
the tree is likely to suffer in the     
following season and no fruit be        
matured4  ,proleptic branches may also  
be due to the shooting out of accessory 
buds--i4e4 extra buds found in or near  
the leaf-axils of many plants1 such as  
,willow1 ,maples1 ,cercis1 ,robinia1    
,syringa1 ,aristolochia1 etc4--which do 
not normally come to anything1 or do so 
only if a surplus of food materials is  
provided4  ,dormant buds1 or            
preventitious buds1 are such as receive 
no sufficient supply of water and food  
materials to enable them to open with   
the other buds in ordinary years1 for in
 most trees only the upper buds on the  

branches develop into new shoots4 ,the  
lower buds do not die1 however1 but     
merely keep pace with the growth in     
thickness of the parent branch1 and may 
be elongated sufficiently each year to  
raise the minute tips level with the    
bark1 their proper cambium only         
remaining alive but not thickening the  
bud4  ,when1 by the breaking of the     
branch above the insertion of the       
dormant bud--or by pruning1 defoliation 
by insects1 etc4--the transpiration     
current and supplies of food materials  
are in any way deflected to the minute  
cambium and growing points of the       
dormant buds1 they are stimulated to    
normal growth1 and may grow out as      
epicormic shoots or shoots from the old 
wood4 ,in many cases such epicormic     
shoots are stimulated to grow out by    
suddenly exposing an old tree to more   
favourable conditions of root-action and
 assimilatory activity1 owing to the    
felling of competing trees which        
previously hemmed it in from light and  

air1 and restricted the spread and      
action of its roots in the soil4 ,this  
is often seen in old ,elms1 ,limes1 etc4
  ,it is by such means as the above that
 substitution branches are obtained when
 a leader is broken or cut away4        
,adventitious buds are such as are newly
 formed from callus or other tissues in 
places not normally provided with buds1 
as is often seen on occluding           
wounds--e4g4 stool shoots4 ,they may    
also be developed on roots1 a fact      
utilised in propagating ,bouvardias1    
,horse-radish1 etc41 by means of        
root-cuttings1 and the suckers of ,plums
 and other fruit trees are shoots       
springing from adventitious buds on     
roots4  ,adventitious buds are also     
common on leaves 7e4g4 ,bryophyllum1    
,ferns1 etc471 and are frequently       
induced on them by wounds--e4g4         
,gesneria1 ,gloxinia1 etc4 ,even cut    
cotyledons may develop them1 and pieces 
of leafless inflorescence 7,hyacinth71  
hypocotyl 7,anagallis71 and in fact     

practically any wounded tissue with a   
store of reserve materials may be made  
to develop them3 thus they have been    
found arising from the pith of          
,sea-kale1 and are commonly developed   
from the cut bulb scales of ,hyacinths4 
,apospory and ,apogamy are particular   
cases of the production of vegetative   
buds on the leaves in place of sporangia
 in ,ferns 7,apospory71 and on          
prothallia in place of ,archegonia      
7,apogamy71 in the latter case induced  
by dry conditions and strong            
illumination4   ,,notes ,,to ,,chapter  
,,xxviii4       ,in addition to the     
literature quoted in the notes to       
,chapter      ,,xxvii41 the student     
should consult the works on ,forest     
,botany      for the scattered          
information regarding adventitious buds4
 ,a      good account may be found in   
,buesgen1 ,bau und ,leben unserer       
,waldbaeume1 ,jena1 #ahig4       ,for   
,apospory and ,apogamy1 see ,lang ,on   
,apogamy and the      ,development of   

,sporangia upon ,fern ,prothalli1 ,phil4
 ,trans41      vol4 #aij1 #ahih1 p4     
#ahg1 where the literature is collected4
     ,,chapter ,,xxix4  ,,grafts4       
,grafting--,comparison with             
cuttings--,effects of environment--     
,relations between scion and            
stock--,variation in grafts--           
,grafting and                           
parasitism--,infection--,pollination--,g
rafts-hybrids      --,predisposition of 
,natural grafts--,root-fusions4         
,grafting is a process which consists in
 bringing the cambium of a shoot of one 
plant into direct union with that of    
another1 and is practised in various    
ways1 the commonest of which is as      
follows3  ,one plant--the stock--rooted 
in the ground1 is cut off a short       
distance above the surface of the soil1 
and a shoot from the second plant--the  
scion--cut off obliquely with a sharp   
knife1 is inserted into a cleft in the  
stock1 so that the two cambiums 7and    
sometimes the cortex and pith of each as

 well7 are in close contact3 the scion  
is then tied in position1 the wounds    
covered with grafting wax1 and the whole
 left until union of the tissues is     
completed4 ,this union depends on the   
formation of callus at the cut surfaces1
 and the intimate union of the ingrowing
 cells from each callus4  ,the          
development of the callus follows the   
course described for wounds1 cuttings1  
etc41 and the union is exactly          
comparable to the union of the two lips 
of a healing callus over a wound 7see p4
 #aig74  ,grafting was known and        
practised far back in the ages4 ,virgil 
was well acquainted with the process1   
and ,theophrastus compared it with      
propagation by cuttings4  ,the scion    
differs from a cutting1 however1 in     
having no roots of its own3 it is       
parasitic upon1 or rather is in         
symbiosis with the stock1 the root and  
tissues of which intervene between it   
and the soil4 ,consequently the         
selective absorption1 size and number of

 vessels1 and innumerable other         
physiological and anatomical            
peculiarities of the stock determine    
what and how much shall go up into the  
scion1 while the latter supplies the    
former with organic materials and rules 
what and how much food1 enzymes1 and    
other secretions1 etc41 it shall receive
 to build up its substance4 ,surely1    
then1 if such factors as the nature of  
the soil1 the water and mineral         
supplies1 the illumination1 and the     
various climatic factors of altitude can
 cause variations on a plant direct1    
these and other factors are still more  
likely to be effective on stock and     
scion1 and each must affect the other4  
,nevertheless opinions have differed    
much as to whether any important effect 
is to be seen1 and on no point more than
 on whether the scion can affect the    
stock1 in spite of such examples as     
,cytisus ,adami1 ,garreya on ,aucuba1   
,sunflower on ,jerusalem ,artichoke1    
etc4 ,recent results1 especially of     

experiments with herbaceous plants1 show
 that not only can the stock affect the 
scion 7and vice versa7 directly1 but the
 effect of the changes may be invisible 
on the grafted plant and only show      
itself in the progeny raised from the   
seed of the grafted plant4 ,in other    
words1 variation occurs in grafts either
 directly1 as the results of the effects
 of the environment on the graft1 or    
owing to the interaction of scion and   
stock1 showing as changes in general    
nutrition in the tissues concerned1     
etc41 owing to special reactions of the 
protoplasm of the uniting cells one on  
the other1 and of the results of the    
further protoplasmic secretions1        
sortings1 and so forth1 on the cells    
developed as descendants of these in the
 further growth of the graft3 or        
indirectly1 in that some of these       
changes so alter the nature of the      
special protoplasm put aside for        
reproductive purposes1 that the         
resulting embryo in the seed transmits  

the effects1 and they show as variations
 in the seedling4 ,if these results are 
confirmed they should meet all          
objections that have been urged against 
the transmission of acquired characters4
  ,in fact there are analogies between  
grafting and parasitism which cannot be 
overlooked1 and should not be           
underestimated1 their commonest         
expression appearing in the alterations 
in stature1 habit1 period of ripening1  
and so forth4 ,these analogies are      
easily apprehended when we compare      
parasites like the ,mistletoe1          
,loranthus1 or even such root-parasites 
as the ,broom-rapes and the             
,rhinanthoideae with grafts2 but they   
also exist in the case of many          
fungus-parasites1 and we might almost as
 accurately speak of grafting some fungi
 on their hosts as of infecting the     
latter with them1 especially when it is 
borne in mind that the effect of the    
scion on the stock is by no means always
 to the benefit of the latter1 and that 

there are reasons for regarding the     
action of some such unions as that of a 
sort of slow poisoning of the stock by  
the scion4 ,why do we not here say that 
the stock has been infected by the      
scion8  ,the resemblances between       
pollination and the infection by fungus 
hyphae may also be insisted upon4 ,if we
 take into account ,darwin's remarkable 
experiments showing that in illegitimate
 unions the pollen exerts a sort of     
poisonous action on the stigmas or      
ovules1 it is possible to arrange a     
series of cases starting with perfectly 
legitimate pollinations where the pollen
 tube feeds as it descends the style on 
materials provided by the cells1 and    
proceeding to cases where the pollen is 
more and more merely just able to       
penetrate the ovary and reach the       
ovules1 to the extreme cases where no   
union at all is possible4  ,side by side
 with such series could be arranged     
analogous cases where fungus spores can 
enter and infect the cells of the host1 

and live symbiotically with or even in  
them1 or can penetrate only with        
difficulty1 or with poisonous effects1  
and finally cannot infect the plant at  
all4  ,less obviously1 but nevertheless 
existing1 are gradations in grafting to 
be observed1 where one and the same     
stock may be successfully combined with 
a scion which improves it--or which is  
improved by it--or the scion may unite  
but acts injuriously on it1 or1 finally1
 cannot be induced to unite4  ,but we   
may go further than this in these       
comparisons4 ,just as the results of    
pollination frequently induce           
far-reaching effects on distant         
tissues--e4g4 the swelling of ,orchid   
ovaries1 and rapid fading of the floral 
organs--so also the effects of hyphae in
 the tissues may induce hypertrophies1  
deflection of nutrient materials1 and   
the atrophy of distant parts--e4g4 the  
curious phenomena observed in ,euphorbia
 attacked by ,uromyces--and some of the 
distant actions in grafts may be        

compared similarly4  ,going still       
further1 we may compare the effects of  
cross-breeding or of hybridisation1     
where the progeny show that changes have
 resulted from the mutual interactions  
and reactions of the commingled         
protoplasm1 with ,daniel's results1 in  
which he obtains proof of such          
interactions of the commingled          
protoplasmic cell-contents of grafts in 
the seedling progeny2 although there is 
no probability--we may even say         
possibility--in this latter case that   
the effects are due to nuclear fusions1 
but only that the germ-plasm of the     
seed-bearing plant has been affected by 
the changes in the cell-protoplasm which
 nourishes it when the reproductive     
cells are forming4  ,in the case of     
graft-hybrids the matter appears to be  
somewhat different1 and we may well     
suppose1 with ,strasburger1 that the    
commingling of characters observed in   
flowers1 fruits1 foliage1 etc41 on      
shoots borne after grafting are due to  

the occurrence of nuclear fusions during
 the union of the grafted tissues2      
though it is by no means impossible that
 what has really happened is profound   
alterations in the nuclear substance    
7germ-plasm7 owing to its being         
nourished by cell-protoplasm            
7somato-plasm7 which has been itself    
affected by the interchanges of         
substance between scion and stock1 and  
therefore itself furnishes a different  
nutrient medium from the unaltered      
cytoplasm of either4  ,but even here we 
can find parallels among the ordinary   
phenomena of plant reproduction4 ,maize 
plants with white endosperm containing  
starch1 if crossed by pollen from other 
plants with purple endosperm containing 
sugar1 bear seeds with purple endosperm 
containing sugar1 and such ,xenia may be
 compared to graft-hybrids in many      
respects4  ,i know of no case among     
fungus infections which could be        
compared directly with these examples1  
and it is not at all likely that we     

shall meet with any instance of a       
fungus-hypha handing over nuclear       
substance to an egg-cell1 and so        
affecting the latter that an embryo     
results4 ,but the case is not           
hypothetically impossible1 although the 
distant relationships of the two groups 
of organisms render it extremely        
improbable among the higher plants4 ,it 
is by no means so improbable1 however1  
that further research may show cases    
where the egg-cell of a lower           
cryptogam--e4g4 another fungus--may be  
affected either directly1 or indirectly1
 by the protoplasm of a parasitic or    
symbiotic hypha1 as suggested by the    
extraordinary phenomena of symbiosis4   
,some of the variations in grafted      
plants are found to predispose the plant
 to disease1 or the reverse1 and cases  
may be cited where the resulting shoots1
 foliage1 or fruits1 or seedlings more  
readily fall a prey to1 or resist1      
parasitic fungi and insects than the    
ungrafted plants4 ,daniel gives         

instances of such--e4g4 among other     
examples1 ,peas grafted on ,beans yield 
seeds which suffer more from ,erysipheae
 than the normal seedlings4 ,but the    
best known cases are those of ,vines in 
their relations to ,phylloxera1 already 
referred to 7p4 #aee74  ,several        
instances are also known where grafted  
plants show more or less resistance to  
such factors of the environment as low  
temperatures2 grafted or budded ,roses  
often suffer much from ,erysipheae1 and 
so forth4 ,much research is still needed
 to determine how far these matters     
depend on real alterations in the nature
 of the graft1 or are only true for the 
localities in which the experiments have
 been made1 a point which has1 ,i think1
 been overlooked by all observers4      
,grafted plants are apparently very much
 exposed to injury by slugs1 insects1   
and the invasions of parasites during   
the healing of the callus and the fusion
 process4 ,here again it must not be    
overlooked that the callus is1 so to    

speak1 a tit-bit of luscious1           
thin-walled1 succulent tissue2 and1 like
 all wounds1 the graft affords entrance 
to parasites such as ,nectria and       
,ascomycetes of various kinds1 under    
circumstances very favourable to their  
invasion4  ,natural ,grafts4--,it is by 
no means an uncommon event to find the  
branches of ,beeches1 ,limes1 and other 
trees which have been accidentally      
brought into contact during growth1     
joined where they cross4 ,as they press 
one against the other1 they become      
naturally grafted1 by that form of the  
process known as inarching3 except that 
in artificial inarching the operator    
cuts off the cortical tissues of the two
 branches and brings their cambial      
surfaces together1 whereas in nature the
 cambiums only come into contact after  
the destruction by pressure1 or slight  
abrasion1 of the entrapped intervening  
tissues4 ,the fusion occurs1 in fact1   
exactly as in the burying-in of a nail  
or wire1 referred to on p4 #baa4        

,natural grafts are very common among   
the roots of trees1 and possibly explain
 some queer cases of the apparent       
revivification of stumps of trees not   
usually given to forming abundant stool 
shoots4 ,it is regarded as probable in  
some old forests that the majority of   
the roots of trees of the same species  
are linked up together by such natural  
grafts1 a probability not diminished by 
the fact that such roots cross at many  
points1 and are easily grafted4         
,,notes ,,to ,,chapter ,,xxix4          
,the student should read ,bailey1 ,the  
,nursery ,book1 #ahif1 for      details 
regarding the practice of grafting1 and 
facts in      abundance can be obtained 
from the pages of the ,gardeners'       
,chronicle4       ,concerning           
graft-hybrids and the variations of     
grafted plants      see ,jouin1 ,can    
,hybrids be obtained by ,grafting8 and  
especially ,daniel1 ,la ,variation dans 
la ,greffe1 in ,ann4 des      ,sc4      
,naturelles1 ,s4 ,,viii41 ,vol4 #h1     

#ahih1 p4 #a1 and the      literature   
there collected4 ,the whole subject is  
largely      controversial1 and much    
work remains to be done4     ,,chapter  
,,xxx4  ,,life ,,and ,,death4           
,protoplasm--,hypothesis as to its      
structure and behaviour--               
,assimilation--,growth--,respiration--,m
etabolism--,action of the               
environment--,nuclear                   
protoplasm--,pollination--,grafting--   
,parasitism--,graft-hybrids--,life--,dea
th--,variation--,disease4   ,we have    
seen that all the essential phenomena of
 disease concern only the living        
substance--the protoplasm--of the plant1
 and that however complex the symptoms  
of disease may be1 the occurrence of    
discolorations1 lesions1 hypertrophies1 
and so forth are all secondary matters  
subsidiary to the fundamental           
alterations of structure and function   
constituting the disease4 ,it remains to
 see if we can adopt any hypothesis as  
to the nature of this physical basis of 

life--the protoplasm--which shall help  
us to understand still more clearly in  
what must reside those processes which1 
so long as they proceed harmoniously and
 uninterruptedly1 constitute life and   
health1 and which when interfered with  
result in disease and death4 ,the       
protoplasm of the living plant-cell     
looks like a slimy translucent mass     
which has been superficially compared in
 appearance to well-boiled sago or clear
 gum4 ,fifty years of observations and  
experiments with it have convinced      
physiologists that it is not a mere     
solution or emulsion1 however1 or even a
 chemical compound in the ordinary sense
 of the term1 although chemical analysis
 gets little out of it beyond water1    
proteids1 carbohydrates and fats1 and   
traces of certain mineral salts2 for    
living protoplasm does not respond to   
the laws of physics and mechanics in    
obeying them1 simply as do ordinary     
solutions and liquids4 ,on the other    
hand1 the most delicate chemical        

manipulation fails us1 because when     
killed it is no longer protoplasm4 ,nor 
does the microscope advance matters far1
 beyond convincing us that this         
marvellous material must have a         
structure far more intimate than        
anything visible to the highest         
magnifying powers at our disposal4      
,nevertheless1 some information is      
forthcoming from the comparative        
examination of the protoplasm of        
numerous different kinds of organisms1  
for we have learnt that certain         
ingredients and no others are necessary 
for its composition--namely1 carbon1    
hydrogen1 oxygen1 nitrogen1 phosphorus1 
sulphur1 calcium,note3 ,see note at end 
of chapter41 magnesium1 potassium--and  
it is as a rule of no use trying to     
foist on to it any substitute for any   
one of these4 ,moreover1 these chemical 
elements must be given in certain       
definite proportions and forms3 for     
instance it is of no use to offer the   
carbon and sulphur in such a form as    

carbon disulphide1 or the nitrogen and  
hydrogen in that of hydrocyanic acid1   
but the carbon must be given to the     
protoplasm in the form of a carbohydrate
 or in some similar form1 the nitrogen  
as an ammonium salt1 nitrate or proteid1
 the sulphur as a sulphate1 and so      
forth1 and thus water1 air1             
carbohydrates1 and the nitrates1        
sulphates1 and phosphates of potassium1 
calcium1 and magnesium become the chief 
natural sources of the essential        
ingredients4 ,again1 we have learnt that
 while there are different forms of     
protoplasm in the cell1 and that these  
react on each other1 and go through     
cycles of arrangement and               
rearrangements1 the intimate structure  
must be of that kind termed             
molecular--beyond the region of vision1 
just as is the microscopic structure of 
a crystal2 but1 while like the latter   
affording evidence of order and sequence
 when properly examined1 the structural 
arrangements and changes must be        

infinitely more complex4  ,all these1   
and numerous other results of enquiry1  
have led to the conclusions that we must
 regard living protoplasm as a complex  
made up of very large molecular units1  
each containing atom-groupings of the   
elements named2 and1 partly on account  
of the large number of atoms they       
contain1 and partly due to the          
vibrations of absorbed heat1 these units
 must be extremely labile4 ,moreover1   
they are linked up into an invisible and
 intricate meshwork1 bathed in a watery 
liquid held in the interstices somewhat 
as water is held in a sponge4 ,in this  
imbibed liquid are dissolved the        
substances1 consisting of the same      
elements1 which are to serve as food1   
and which are to be taken up into the   
molecular framework and built up into   
the structure of new molecular          
units--or1 as they may be shortly       
termed1 molecules of protoplasm3 in the 
bathing liquid are also dispersed the   
fragments--again containing the elements

 named--which have resulted from the    
breaking asunder of some of the complex 
protoplasm molecules1 and which are     
partly destined to be used up again1    
partly to be burnt off in respiration1  
and partly to be put aside as metabolic 
products such as reserves1 secretions1  
permanent structure1 etc4 ,among the    
elements carried into this liquid and   
dissolved in it the free oxygen of the  
air also plays an important part4  ,as  
new molecules are formed1 by mutual     
combinations of the food-materials      
selected by molecular attractions1 they 
are taken up into the protoplasmic      
framework1 and built in between those   
already in existence1 thus distending   
the whole1 and we say that the          
protoplasm ,assimilates food-materials  
and ,grows4 ,when distended beyond a    
given degree1 or disturbed in various   
other ways1 the molecular framework     
breaks1 and some of the molecules are   
shattered1 and as they fall to pieces   
certain of their constituent parts      

containing carbon and hydrogen forcibly 
combine at the moment of liberation with
 the oxygen in the fluid around and are 
burnt off in the form of carbon-dioxide 
and water1 heat being of course evolved4
 ,this is the fundamental process of    
,respiration4  ,it is probably the      
alternation of these processes of       
,assimilation--the building up into the 
protoplasmic structure of new complex   
labile molecules--and ,destruction--the 
shattering of such molecules with       
redistribution1 oxidation1 etc41 of     
their fragments--which constitute the   
fundamental process of life4 ,different 
authorities attempt to explain the      
details of these processes in various   
ways1 but there is practical agreement  
on the one point1 that life consists in 
the alternate building up of new        
protoplasm from the                     
food-materials--,assimilation--and the  
breaking down of the molecular complexes
 to simpler ones--,disintegration1 or   
,dis-assimilation1 as we may call it4   

,during the periods when assimilation   
prevails1 and the protoplasm increases  
in mass1 we recognise ,growth1 and since
 this is usually associated with the    
vigorous imbibition of water1 owing to  
the powerful osmotic attractions for    
that liquid exhibited by some of the    
products1 and with consequent further   
stretching of the invisible molecular   
plexus1 the growth may be so evident in 
increased size1 that we are accustomed  
to look upon the visible increase in    
volume alone as growth2 but it is       
essential to understand that growth of  
the protoplasm is always proceeding     
during life1 even when as many older    
molecules are being shattered and       
dispersed as new ones are being formed  
by assimilation1 and when1 therefore1 no
 visible permanent enlargement occurs4  
,similarly1 during periods when         
disintegration of the molecules         
prevails1 we must not assume that the   
assimilation of new molecules is not    
occurring and that growth is not        

proceeding4 ,the two processes are      
always going on during the active life  
of the protoplasm3 in fact life consists
 in the play of these processes1 as     
already said4  ,that numerous chemical  
rearrangements of the atom-complexes    
take place outside the protoplasmic     
molecules--both of those left unemployed
 in assimilation and of those rejected  
during the destructive processes--will  
be readily understood3 many of the      
bye-products found in plants1 such as   
vegetable acids1 alkaloids1 colouring   
matters1 crystalline bodies1 etc41 etc41
 are due to these1 so to speak1         
fortuitous combinations and             
re-combinations4  ,the part played by   
respiration has often been              
misunderstood4 ,it consists in the      
burning off of some of the carbon and   
hydrogen of the shattered protoplasm    
molecules1 by means of the oxygen of the
 air1 which finds its way into the      
fluids around the protoplasm1 and when  
it is active every act of               

combustion--which is here an            
explosion--leads to the shattering of   
more protoplasm molecules1 and          
consequently to more respiratory        
combustion of the products4 ,if the     
supply of oxygen is limited the breaking
 down of the molecules of protoplasm    
does not cease1 but the carbon and      
hydrogen which would otherwise have been
 oxidised are now in part left to form  
other compounds in the surrounding      
liquid1 and thus incompletely oxidised  
bodies1 such as vegetable acids1        
alcohols1 etc41 accumulate4 ,even in the
 complete absence of atmospheric oxygen 
the protoplasm may go on breaking down  
and accumulating various compounds      
containing relatively much carbon and   
hydrogen--so-called intramolecular      
respiration2 but in ordinary plants this
 process soon comes to an end1 because  
the blocking up of the molecular plexus 
leads to obstruction and interferes with
 the normal assimilation and            
dis-assimilation1 and1 if prolonged1    

leads to pathological conditions1 and   
eventually death4  ,here1 then1 we meet 
with a cause of disease1 or of          
predisposition to disease4 ,the         
deprivation of oxygen interferes with   
the normal processes of building up and 
breaking down of the protoplasmic       
molecules1 and bodies we term poisonous 
accumulate and may lower the vitality or
 even bring life to an end4  ,during    
normal life other products of the       
disruption of the protoplasm molecules  
are nitrogenous bodies1 such as         
proteids1 and these we have reason to   
believe are used up again1 acting as the
 nuclei1 so to speak1 of the new        
molecules1 and so being built up again  
with fresh food-materials into the      
plexus1 to be again set free1 and again 
used up1 and so on4 ,others are the     
carbohydrates1 such as cellulose1 which 
pass out of the molecule into an        
insoluble form1 and are accumulated     
outside the protoplasm in the form of   
cellulose membranes1 and so forth4 ,it  

is these formed products of metabolism  
7,metabolites71 especially cellulose and
 bodies which result from its subsequent
 transformation1 which constitute the   
main permanent mass of the ordinary     
plant4  ,we are now in a position to see
 how another fundamental cause of       
disease or predisposition to disease    
exists in the deprivation of the        
protoplasm of any of the elements needed
 to supply--in the food-materials--the  
place of those which have been          
permanently put aside in the form of    
cell-walls1 or burnt off in respiration1
 passed out as excretions1 or in other  
ways lost4  ,it is clear that the       
indispensability of an element must mean
 that the protoplasmic molecule cannot  
be completed without it3 the same       
conclusion is supported by the          
experimental proof that these elements  
cannot be replaced by chemically similar
 elements4  ,it does not follow1        
however1 that the protoplasm molecule   
must always have the same number of     

atoms of these elements1 and grouped    
always in the same atom-complexes before
 being assimilated2 nor that the        
protoplasm molecule1 when once built up1
 always breaks down in exactly the same 
way4 ,on the contrary1 while the        
protoplasm of corresponding parts of a  
daisy and of a rose must contain all the
 elements named1 we must believe that   
the atom groupings are different in the 
protoplasm molecule in each case2 and   
though the molecules of the             
cell-protoplasm1 of the nucleus1 of the 
chlorophyll-corpuscles1 etc41 of one and
 the same plant must have all these     
elements1 the atom groupings and modes  
of building up and breaking down may be 
very different in each case4  ,again1   
the cell-protoplasm1 bathed by the sap  
taken in by roots from the soil or fed  
directly by that derived from the       
leaves1 must be exposed to very         
different stimuli and modes of          
nourishment1 etc41 from those incurred  
by the protoplasm of the nucleus which  

it encloses3 and similar conclusions    
must apply in turn to the protoplasm of 
the root in the dark moist soil and of  
the leaf in the light dry air1 or to    
that of the superficial epidermis cells 
as contrasted with that of the deeply   
immersed pith1 and so on4  ,it is no    
doubt in these directions that we must  
seek for the explanation of many        
life-phenomena at present quite beyond  
explanation4 ,thus1 it is tolerably easy
 to modify the action of the            
cell-protoplasm of a plant1 by exposing 
it to differences of illumination1      
temperature1 moisture1 and so forth1    
within certain limits2 at least1 since  
the changes in stature1 tissue          
differentiation1 cell-secretions1       
flowering capacity1 etc41 of plants     
affected by such factors of the         
environment--e4g4 alpine plants brought 
into the plains--must be due to changes 
in the mode of activity of the          
protoplasm1 we must assume that the     
above factors affect the latter4 ,but it

 is extremely difficult to reach the    
nuclear-protoplasm directly by such     
stimuli1 as proved by the experience    
that even where we allow the factors to 
act for a long time1 no permanent change
 can be detected in the behaviour of the
 nuclear-protoplasm--the essential      
material in the reproductive organs and 
reproductive process4 ,at least we must 
infer that no change has been           
permanently stamped on this nucleo-plasm
 from such facts as the characters of   
the seedlings of the progeny of the     
plain-raised plants3 if they are again  
sown in an alpine situation they        
forthwith behave again as alpines4      
,must we not conclude1 then1 that this  
difficulty of reaching the              
nuclear-protoplasm is owing to the fact 
that it is nourished and influenced     
directly only by the cell-protoplasm8   
,that the cell-protoplasm is its        
environment1 and not so directly the    
outer world8 ,we may influence the      
cell-protoplasm--we may make it work    

harder or less actively1 respire        
vigorously or slowly1 build up and break
 down in various different ways1 or at  
different rates1 and so forth1 within   
limits2 but it is nevertheless          
cell-protoplasm of its specific kind1   
with its own range of molecular         
variations and activities within these  
limits1 and it supplies the             
nuclear-protoplasm with what it wants so
 long as these limits are not exceeded4 
,consequently1 while it is very easy to 
make the cell-protoplasm vary within the
 limits of its range1 it is not easy to 
induce it to vary its effects on the    
nuclear-protoplasm to such an extent or 
in such a way that the latter is        
permanently or materially altered in    
constitution4  ,nevertheless it would   
appear that cases do occur where the    
nuclear-protoplasm is reached and       
affected by external stimuli1 as evinced
 by some of the phenomena of            
hybridisation and of cross-and          
self-fertilisation1 because we find the 

results expressed in the mingling of the
 characters of parents1 in strengthened 
or enfeebled progeny1 and even in the   
appearance of unexpected properties1    
which1 from the facts of ,reproduction1 
we know must have taken their origin in 
some alteration of the nuclear substance
 of the embryo4  ,here1 however1 we know
 in most cases that the principal agent 
which has reached the                   
nuclear-protoplasm1 is another portion  
of nuclear-protoplasm4 ,in              
hybridisation1 one which has been fed   
and influenced by cell-protoplasm of a  
very different plant2 in                
cross-fertilisation1 one fed and        
influenced by the cell-protoplasm of a  
different plant of the same species1 and
 in self-fertilisation1 one fed and     
influenced by the same cell-protoplasm4 
,that somewhere1 and somehow1 such      
nuclear-protoplasm as induces the       
changes in the characters of hybrids1   
etc41 has been influenced by its        
immediate environment--the              

cell-protoplasm of the plant--appears to
 be a conclusion from which there is no 
escape4 ,we may obtain similar evidence 
from the experience of grafting4 ,it is 
relatively easy to influence the        
cell-protoplasm of a scion by a suitable
 stock1 obviously because the latter1   
while handing on to the former all      
necessary materials from the soil1      
presents the indispensable elements and 
compounds in somewhat different         
proportions1 dilutions1 etc41 from those
 which its own roots would have done1   
and probably mingles with them a certain
 amount of its own peculiar products1 as
 well as affects the modes of working   
and interaction of both by the molecular
 impetus impressed on them4             
,consequently the cell-protoplasm of the
 scion1 while obtaining from the stock  
all it needs within the limits of its   
own variations of structure and         
activity1 nevertheless builds up and    
breaks down in ways or at rates slightly
 different from those hitherto normal to

 it1 and perceptible variations result  
when the sequences and correlations of  
these material and mechanical changes   
have affected a sufficiently large mass 
for the accumulation of visible effects4
 ,the limits to grafting suggest not    
that an inappropriate stock does not    
offer to the protoplasm of the scion the
 right materials1 but that it presents  
them in proportions and in forms which  
are unsuitable for the assimilable      
powers of the latter1 or1 possibly1     
mingled with substances poisonous in    
themselves or capable of becoming so in 
conjunction with bodies in the scion4   
,what has been said of the action of    
stock on scion1 will also be true1      
mutatis mutandis1 of the reciprocal     
action of scion on stock4 ,here again we
 may have causes for disease1 or        
predisposition to disease4  ,it         
occasionally happens1 however1 that the 
nuclear protoplasm of the stock or scion
 is affected in grafting1 and we infer  
from the difficulty of modifying it in  

any other way in ordinary reproduction  
than by means of other nuclear          
protoplasm--e4g4 in hybridisation--that 
in such cases a fusion of the nuclei of 
stock and scion has occurred during the 
grafting1 and a graft-hybrid has        
resulted--e4g4 ,cytisus ,adami4  ,it is 
not impossible however that the nuclear 
protoplasm has in such graft-hybrids    
been subsequently modified by the       
differences in nutrition to which it has
 been subjected1 in the modified        
cell-protoplasm affected by the mingling
 of the juices1 etc41 of scion and      
stock2 for it is quite conceivable that 
such materials may affect the protoplasm
 far more profoundly than anything      
derived directly from the environment4  
,if ,daniel's researches are confirmed1 
however1 it appears that in some cases1 
at any rate1 the nuclear-protoplasm is  
so altered by the grafting that when the
 new embryo is developed1 after fusion  
with nuclear substance from another     
plant of the same species1 the results  

are apparent only in the progeny1 and   
the effects of alteration in the        
cell-protoplasm have been transmitted to
 the nuclear protoplasm of the          
germ-cells--i4e4 acquired characters    
have been transmitted and fixed by      
heredity4 ,should this prove true the   
importance of the results can hardly be 
over-estimated4 ,the matter is too      
problematical for further discussion    
here1 but we see that any such action   
may profoundly affect the constitution  
of the resulting plant4  ,turning now to
 the case of fungi or other organisms   
which obtain access to the              
cell-protoplasm4 ,at the one extreme we 
have cases where the protoplasm of the  
diseased plant is rapidly and directly  
poisoned and destroyed1 as in the       
killing off of seedlings in ,damping    
,off3 near the other extreme we have    
cases where the foreign protoplasm of   
the parasite1 although it gains complete
 access to that of the host1 merely     
stimulates the latter to greater        

activity and itself works for its own   
ends in conjunction with it--e4g4       
,plasmodiophora4 ,in such instances we  
must figure to ourselves the cells of   
the root of the ,crucifer handing on    
food-materials to both masses of        
protoplasm--that of the ,plasmodiophora 
and that of the cell into which it      
penetrates2 and it is immaterial whether
 both obtain the food-materials         
directly1 or1 what seems more likely1   
the fungus only at second hand and by   
the medium of the host's protoplasm4 ,in
 any case1 the latter is for a long time
 at least not poisoned or maimed1 or in 
any perceptible way injured by excreta  
from the fungus-protoplasm1 although it 
is evident that each must excrete       
various metabolites which may soak into 
and be taken up by the other3 on the    
contrary the host-protoplasm grows      
larger1 attracts more food supplies1    
makes larger cells1 and is evidently    
stimulated to greater activity for the  
time being1 its behaviour reminding us  

of the stimulation of cells by means of 
slight doses of poison referred to      
previously4 ,we must therefore assume   
that the general course of building up  
and breaking down of its                
protoplasm-molecules go on as usual--or 
nearly so--in both the host cell and the
 invader2 and that the assimilatory1    
respiratory1 excretory and other        
functions are carried on in the former  
as in the normal cell1 or are but       
slightly modified to an extent which    
does no immediate injury to its life4   
,but we must further assume that the    
same is also true of the invading       
protoplasm1 and that the ,plasmodiophora
 is also supplied with suitable         
atom-complexes to build up its          
protoplasm molecules1 as fast as they   
are shattered and the rejecta burnt off 
in respiration4  ,a step further1 and we
 come to instances of ,symbiosis1 where 
the commingled masses of protoplasm of  
host and invader continue this          
harmonious action during life4 ,clearly 

there are resemblances between these    
latter cases and successful grafts1 and 
between both and successful sexual      
unions where the resulting embryo-cell  
gives rises to a vigorous and healthy   
plant2 and the more these resemblances  
are examined in the light of what we    
know of symbiosis the more they support 
our contention4  ,such considerations as
 the foregoing suggest1 then1 that life 
consists in the regular and progressive 
building up and breaking down of the    
complex protoplasm molecules1 and is    
necessarily accompanied by the influx of
 the indispensable food-elements in     
certain combinations and atom-complexes 
for assimilation1 and by the combustion 
of some of the debris of the shattered  
molecules1 which combine with the oxygen
 in respiration and so afford explosions
 which raise the temperature and enhance
 the lability of existing molecules1 and
 act as stimuli to the shattering of    
further molecules4 ,the results of these
 rhythmical buildings up 7assimilation7 

and shatterings 7dis-assimilation7 of   
the protoplasm molecules are the growth 
of the protoplasm1 with further         
intercalations of water and new         
food-supplies1 etc41 on the one hand1   
and the formation of metabolic products 
7proteids1 cellulose1 sugars1 fats1     
etc471 some of which are again used up1 
others respired1 others deposited as    
stores1 cell-walls1 etc41 on the other4 
,that the building-up process depends on
 the action of molecular forces         
comparable to those by which a growing  
crystal goes on selecting atom-complexes
 of its particular kind from the        
solution around seems highly probable1  
and this being the case we can          
understand how under certain            
circumstances substitutive selections   
may occur4 ,that is to say1 just as a   
crystal will sometimes build up into its
 structure atom-complexes of a kind     
different from its normal molecules1 so1
 given the proper conditions1 a         
protoplasmic molecular unit will build  

up into its structure atom-complexes    
somewhat different from those it had    
hitherto taken up--i4e4                 
assimilated--with consequent            
modifications of its behaviour4 ,if this
 occurs1 the modes of further building  
up and breaking down will be affected by
 the subsequent action of these slightly
 modified protoplasm units1 and it may  
well be that the whole significance of  
variation turns on this4 ,whether the   
resulting variation makes for the       
welfare or otherwise of the organism    
will then be decided by the struggle for
 existence1 and the natural selection   
which ensues4 ,such a view also implies 
that the energy concerned is primarily  
what is usually termed chemical energy1 
and that every compound entering into   
the protoplasm carries in a supply of   
this1 available in various ways4        
,death1 on the contrary1 is the         
cessation of these rhythmical processes 
of building up and breaking down of the 
protoplasm molecules4 ,it does not imply

 the cessation of chemical changes of   
other kinds1 but that these rhythmical  
constructions of the complex and labile 
protoplasm molecules breaking down on   
stimulation to bodies partly            
re-assimilable1 partly combustible in   
respiration1 and partly excretory1 etc41
 have ceased1 and that further chemical 
changes in the material are thenceforth 
simpler and different in kind and       
degree1 eventually leading to total     
disintegration so that no units are left
 capable of restoring the rhythm4  ,if  
these ideas are correct1 we may define  
,disease as dangerous disturbances in   
the regularity1 or interference with the
 completeness or range of the molecular 
activities constituting normal          
,life--i4e4 ,health--and it is evident  
that every degree of transition may be  
realised between the two extremes4 ,now1
 if we further assume1 as ,i think we   
must do1 that a considerable range or   
play must exist in the molecular        
activities of the protoplasm            

constituting life1 we obtain a sort of  
expression of what we mean by limits of 
variation4 ,the fact that life can go on
 in a given plant at temperatures       
between from #a deg4-#e deg4 and #ce    
deg4-#dj deg4 ,c41 or in lights of      
different intensity1 or within          
considerable ranges of water supply1    
concentration of salts1 partial pressure
 of oxygen1 etc41 implies that the      
molecular activities of the protoplasm  
are of the normal kind all the time1    
though they may differ in rapidity1 and 
even in quantitative and qualitative    
respects within certain limits2 and the 
meaning of the optimum temperature1     
illumination1 oxygen pressure1 etc41 is1
 from this point of view1 not that the  
molecular activities differ in kind from
 those nearer the minima and maxima1 so 
much as that they are running at the    
best rates for the welfare of the       
plant--i4e4 for permanent health4  ,if  
we transcend the cardinal points        
limiting the range of this play1        

however1 and we get variations in the   
kind as well as rates of molecular      
constructions and disruptions1 then we  
pass by imperceptible gradations into   
ill-health--i4e4 ,disease4  ,and        
similarly in relation to other          
protoplasm4 ,that of the right kind of  
pollen grain from another plant of its  
own species1 stimulates the contents of 
the ovule to produce a vigorous embryo  
and healthy seedling3 that of a similar 
pollen grain in its own flower either   
does no positive harm1 but has a feebler
 effect1 or it may act like a poison4   
,that of another pollen grain again may 
refuse to unite at all2 while that of a 
fungus hypha--e4g4 of ,sclerotinia on   
,vaccinium--may run down the style as   
does the pollen tube and produce death  
and destruction throughout the ovule4   
,or again1 in ,clover1 we may have the  
hypha of a ,botrytis with its protoplasm
 unable to do more than penetrate into  
the cellulose walls and diffuse a poison
 into the adjacent cells1 being utterly 

incapable of directly facing1 or        
mingling with the living protoplasm of  
such cells1 whereas the protoplasm of   
another organism--e4g4 ,rhizobium--will 
penetrate directly into the cells1 live 
in them for weeks or months without     
injury--nay even with advantage to their
 life4 ,and hundreds of similar cases   
can be selected4  ,we may1 therefore1   
conclude that ,variation depends        
fundamentally on alterations in the     
structure or mode of building up and    
disintegration of the protoplasmic      
molecular unit1 brought about either by 
direct modifying action of the inorganic
 environment--nutrition1 temperature1   
oxygen supply1 light1 etc41 etc4--or by 
the mingling with it of other           
protoplasm1 the molecules of which since
 they have already a slightly different 
composition1 configuration1 mode of     
breaking down and building up1 etc41    
affect its molecules by supplying them  
with altered nutritive atom-complexes1  
by competing with them for oxygen1 etc41

 etc4 ,once these molecules are         
affected1 we must assume that long      
sequences of other chemical and         
molecular changes will be also modified2
 and although we have no conception of  
how these changes bring about changes in
 form1 that they do so is only a        
conclusion of the same order as that    
which we hold regarding the much simpler
 changes concerned in the formation of  
crystals4  ,that such variations may be 
of every degree as regards profundity1  
permanence1 kind1 etc41 may well be     
imagined2 and there is nothing          
surprising in our being able to induce  
them more easily by the action of       
external factors in the readily         
accessible cell-protoplasm than in the  
less exposed nuclear-protoplasm2 because
 the latter is only accessible through  
the former1 or through the agency of    
other nuclear protoplasm already        
modified4 ,on these and similar         
phenomena depend the relative permanency
 and transmissibility of the variations4

 ,our measure of the latter only begins 
when the effects referred to have become
 manifest in large masses of cells1     
because only then do they become        
appreciable to our senses4  ,further1   
variations thus induced may be of       
advantage to the continued life of the  
plant1 or in all degrees disadvantageous
 or threatening to its existence4 ,these
 latter variations are ,disease1 and if 
their interference with the normal      
rhythmical play of the building up and  
breaking down of the protoplasm         
molecules proceeds beyond certain       
limits1 life ceases1 and we have death  
supervening on disease4   ,,notes ,,to  
,,chapter ,,xxx4       ,it appears      
probable that calcium is not always     
needed by      living cells1 and may not
 enter into the composition of          
protoplasm2 on the other hand traces of 
iron are perhaps      necessary4        
,the criticisms and summary of facts on 
which the hypothesis      regarding     
protoplasm here adopted is based are    

developed at      length in ,kassowitz1 
,allgemeine ,biologie1 ,wien1 #ahii1 ,b4
 ,i4      and ,,ii41 where the collected
 literature may be found1 and the       
reader introduced to the huge mass of   
controversial writings      put forward 
since ,darwin and associated with the   
names of      ,weismann and others4     
,it will probably be noticed that ,i    
have employed the term      molecular   
unit of protoplasm1 and have not        
discussed the      question of organised
 structure in the latter3 this is       
because      it seems clear to me that  
living protoplasm as such does not      
possess organised structure in the true 
sense of that      term--it is1 rather1 
busy preparing and making organised     
structure1 and a molecular constitution 
would have to be      ascribed to all   
physiological units of the nature of    
micellae1 pangens1 ids1 etc41 as truly  
as to the structural      units of a    
starch-grain or cell-wall1 or even of a 
crystal4 ,in      this connection1 the  

student will find the necessary points  
of      view put forward in ,pfeffer1   
,physiology1 pp4 #cg-hc4     ,,index4   
,absorption by roots1 #di4              
,absorption of energy1 #bc4             
,absorption of light1 #bg4              
,absorption of water1 #ej4    ,abutilon1
 #ahc4    ,acarus1 #hh4    ,accessory   
buds1 #bei4    ,acer1 #bad4    ,acid    
gases1 #aha1 #aia4    ,acids1 #acj1     
#acf4    ,acquired characters1 #bhc4    
,acrostalagmus1 #bch4    ,action of the 
environment1 #bga4    ,adaptation1 #agf4
    ,adapted races1 #agg4    ,adonis1   
#bbj4    ,adventitious buds1 #bbd1 #bbe1
 #beg1 #bfj4    ,a,ecidium1 #hh1 #aad1  
#aaf1 #ahg1 #ahh1 #ahi1 #bag1 #bbc1     
#bbe1 #bcb1 #bdg1 #beb4    ,aeration1   
#ajd4    ,aerobic organisms1 #eg4       
,aetiology1 #hi1 #ajj4    ,agaricus     
melleus1 #aae1 #adc1 #ade1 #bcd4        
,agents of disease1 #aac4               
,aglaospora1 #bbc4    ,agriculture1 #fe4
    ,agricultural ,chemistry1 #b4       
,ajuga1 #bag4    ,albinism1 #agi1 #ahb1 

#ahc1 #ahf4    ,alder1 #bjg1 #bai4      
,aleurone layer1 #agc4    ,algae1 #bae4 
,allium1 #beh4    ,almond1 #afh4        
,alnus1 #bad4    ,aloe1 #acd1 #afa4     
,alpine plants1 #bej1 #bgi4    ,american
 blight1 #afd1 #bai4    ,american vines1
 #aee1 #afi1 #agb4    ,amides1 #ca4     
,amoeba1 #add4    ,amount of energy     
stored1 #be4    ,amygdalin1 #agc4       
,anabaena1 #abh4    ,anaerobic bacteria1
 #eh1 #bcg4    ,anagallis1 #bfa4        
,analyses1 #fe4    ,analyses of waters1 
#eh4    ,anemone1 #bdg4    ,animals1    
#ii1 #ajh1 #adb1 #bjg4    ,antennaria1  
#bcb4    ,anthonomos1 #bdi4    ,anthrax1
 #add4    ,antiseptics1 #afb4    ,ants1 
#bcb4    ,aphis1 #hh1 #aji1 #afa1 #afe1 
#ahh1 #bac1 #bad1 #bcb1 #bda1 #bec4     
,aphrophora1 #bcc4    ,apogamy1 #beg1   
#bfa4    ,aporia ,crataegi1 #ahg4       
,apospory1 #beg1 #bfa4    ,apple1 #agj1 
#aga1 #ahg1 #ahi1 #aib1 #bjf1 #bag1     
#bah1 #bai1 #bbc1 #bbf1 #bca1           
#bcc1 #bdh1 #bdi1 #bec1 #bed4           
,apricot1 #ahh1 #bjf4    ,apricots1     

#bcd4    ,area of root-surface1 #cg1    
#ci4    ,arisarum1 #ahh4                
,aristolochia1 #bei4    ,aroids1 #aac4  
,arrest of growth1 #bdf4    ,arsenic1   
#afb4    ,artificial wounds1 #aid4      
,ascomycetes1 #ahi1 #bag1 #bfi4         
,ascochyta1 #aij4    ,ash1 #ahb1 #bbc1  
#bbe1 #bea4    ,asparagus1 #ahj1 #bcj1  
#bea1 #beb4    ,aspergillus1 #bca4      
,aspergillus niger1 #eh4    ,aspidiotus1
 #ahg4    ,assimilation1 #h1 #ba1 #acc1 
#bga1 #bge1 #bgg1 #bhe1 #bhf4           
,assimilates1 #bgd4    ,atmosphere1 #a1 
#ii4    ,atmospheric influences1 #aja4  
,atrophy1 #bdf1 #bdg1 #bff4             
,attractive substances1 #acf4           
,aucuba1 #bfd4    ,autumnal colouring1  
#aia4    ,autumnal fall1 #ic4           
,avalanches1 #ajf4     ,bacteria1 #ajb1 
#acc1 #adc1 #afh1 #agc1 #agf1 #ahb1     
#aij1 #bjj1 #baf1 #bai1 #bbc1           
#bbg1 #bca1 #bcf1 #bcg4    ,bacteriosis1
 #bbg4    ,barberry1 #agf4    ,bark     
boring1 #bjd1 #bje4    ,bark-beetles1   
#bje4    ,barley1 #agf1 #bdh4           

,barrenness1 #bdf1 #bdi4    ,bats1 #bdd4
    ,bean1 #ahh1 #aij1 #aia1 #bfh4      
,beech1 #aib1 #bbb1 #bbc1 #bbe1 #bcc1   
#bdj1 #bdb1 #bed1 #bfi4    ,beech       
,miner1 #bjh4    ,bees1 #adb1 #adc1     
#afd4    ,beet1 #aib1 #baf1 #bai1 #bcj4 
,beet-rot1 #bcj4    ,beetles1 #aaj1     
#adc1 #ade1 #bje1 #bjf1 #bjg1 #bdh1     
#bed4    ,berkeley1 #he4    ,bilberries1
 #aaf1 #adb1 #bag1 #bah1 #bdh4          
,biology of soil1 #ef1 #ajb4    ,birch1 
#bjg1 #bah1 #bbd4    ,birds1 #ajh1 #add1
 #afd1 #aff4    ,bird's-eye ,maple1     
#bbd4    ,black spots on leaves1 #ahf1  
#ahi1 #aia4    ,bladders1 #bah4         
,blemish1 #aih4    ,blights1 #hf1 #ajd1 
#agi4    ,blisters1 #bcj4    ,blue rays1
 #ba4    ,bombyx1 #ahg1 #bah4           
,bordeaux mixture1 #afb4    ,boring1    
#bjd4    ,botrytis1 #aca1 #acb1 #acf1   
#age1 #bcj1 #bca1 #bdc1 #bhh4           
,boussingault1 #e1 #aj4    ,bouvardia1  
#bfj4    ,bramble1 #aab4    ,branch     
stumps1 #aid1 #aii4    ,brand1 #bdj4    
,breeding1 #gh4    ,briars1 #aac4       

,broom-rapes1 #bfe4    ,browning1 #abb1 
#ahf1 #bce4    ,brown spots1 #ahf1 #ahi1
 #aij1 #aia4    ,browsing1 #bdd4        
,bruchus1 #bdh4    ,bruises1 #aid1 #bjc1
 #bdj1 #bda4    ,bryony1 #aab4          
,bryophyllum1 #bfj4    ,bud galls1 #bai4
    ,bud variations1 #ib1 #ic4    ,bulb 
diseases1 #bbg4    ,buried objects1     
#baa1 #bfi4    ,burning1 #aia4          
,burning-glass effect1 #aib4            
,burrows1 #bjd1 #bje4    ,burrs1 #bbb1  
#bbc1 #bbd4    ,bursting of fruits1     
#bbg1 #bcj4    ,butterflies1 #ade4      
,bye-products1 #bgf4     ,cabbage1 #bec4
    ,cabbage moth1 #bjh4    ,caeoma1    
#beb4    ,caesalpinia1 #bcc4            
,calcium1 #bgb4    ,calcium oxalate1    
#ach4    ,calla1 #ahc4    ,calliandra1  
#bcc4    ,callus1 #aai1 #abj1 #abd1     
#aci1 #adj1 #aif1 #aig1 #aii1 #bja1     
#bjb1 #baj1 #bda1       #bfj1 #bfc1     
#bfi4    ,calyptospora1 #aaf1 #bag4     
,cambium1 #abj1 #aif1 #aii1 #bbb4       
,camellia1 #ahg4    ,cancer1 #abg4      
,canker1 #hg1 #bbb1 #bbc1 #bda4         

,capnodium1 #bcb4    ,capsella1 #aaf1   
#age1 #beb4    ,carbohydrates1 #af1 #ag1
 #bj1 #cd1 #abb1 #ahd1 #bgb1 #bgc1 #bgg4
    ,carbolic acid1 #afb4    ,carbon1   
#bgb4    ,carbon assimilation1 #h1 #aj1 
#bh1 #ajf4    ,carbon-bisulphide1 #afc4 
,cardinal points1 #bhh4    ,carrot1     
#afd4    ,carpocapsa1 #bjg4    ,cast    
branches1 #abc4    ,castor oil1 #agb4   
,caterpillars1 #aji1 #afd1 #bjg1 #bjh1  
#bdd1 #bed1 #bei4    ,cats1 #afd4       
,cattle1 #ajh4    ,cauliflowers1 #bdg1  
#bej4    ,causes of disease1 #hi1 #ii1  
#ajh1 #aei1 #bgh1 #bhb4    ,cecidia1    
#bab4    ,cecidomyia1 #ahb1 #bac1 #bad1 
#bah1 #bai1 #bed4    ,celery1 #ahj1     
#bcj4    ,cell contents1 #afh4          
,cell-protoplasm1 #bgi1 #bhj1 #bij4     
,cellulose1 #acb1 #bgg1 #bhf4           
,celosia1 #bej4    ,centaurea1 #ahh4    
,centhorhynchus1 #bai4    ,cephaleuros1 
#ahh4    ,cephus1 #bdh4    ,cercis1     
#bei4    ,cercospora1 #aij4    ,cereals1
 #bdh4    ,change of conditions1 #gh4   
,charlock1 #afe4    ,checks to disease1 

#aff4    ,chemical analysis1 #cb1 #fd1  
#ajc1 #bgb4    ,chemical antiseptics1   
#aei4    ,chemical energy1 #bi1 #bhg4   
,chemotactic phenomena1 #gb1 #acj1 #ace1
 #acg4    ,chermes1 #aec1 #bbc4         
,cherry1 #bjh1 #bji1 #bca1 #bcd1 #bce1  
#bdg1 #bdh4    ,chestnut1 #aij4         
,chlorine1 #aha4    ,chlorophyll1 #ai1  
#ajf1 #abb4    ,chlorophyll action1     
#ahd1 #aib4    ,chlorophyll corpuscles1 
#i1 #ah1 #bb4    ,chlorosis1 #abb1 #afe1
 #agi1 #ahj1 #aha4    ,chrysanthemum1   
#bdc1 #beb4    ,chytridiaceae1 #abg1    
#acf1 #ahi1 #bjh4    ,cicada1 #bce4     
,cicatrix1 #abc4    ,cinchona1 #afh1    
#agb1 #agc4    ,circulation of carbon1  
#fb4    ,circulation of nitrogen1 #fb4  
,citrus1 #afh4    ,clasterosporium1     
#ahh1 #bji4    ,classification of       
diseases1 #ii1 #aja1 #abj4              
,claviceps1 #bcb4    ,climate1 #a4      
,climbing plants1 #aab1 #aac1 #baj4     
,clostridium1 #bcf1 #bcg4    ,clothes1  
#adb4    ,clover1 #afd1 #ahg1 #bdi1     
#beb1 #bhh4    ,cluster-cups1 #ahh4     

,coal gas1 #ajd1 #ahb4    ,coccideae1   
#afd1 #bcb4    ,coccus1 #bbc4    ,coffee
 leaf-disease1 #aad1 #adf1 #aff1 #afi1  
#bdb4    ,coleophora1 #aec1 #bjf4       
,coleosporium1 #afi4    ,coleus1 #aib1  
#bbj4    ,competition of fungi1 #fa4    
,complex interactions1 #ia1 #ii4        
,conifers1 #abe1 #bje1 #bbc1 #bbe1 #bcd1
 #beh4    ,constitution1 #aef1 #bhc4    
,consumption1 #bdh4    ,contact         
irritability1 #abe1 #ace4    ,contagium 
fluidum vivum1 #ahc4    ,contortions1   
#beb4    ,convallaria1 #age4            
,convolvulus1 #aab4    ,copaifera1 #bcd4
    ,copper sulphate1 #afb1 #afe4       
,coppery leaves1 #aia4    ,cork1 #aai1  
#abc1 #aid1 #aii1 #baf1 #bbb4    ,cork  
wings1 #bag4    ,corky warts1 #bab4     
,corn1 #bdh4    ,corrosion of marble1   
#df4    ,cossus1 #bjf4    ,cost of      
epidemics1 #adf1 #adg4    ,cotton1 #agb4
    ,crassula1 #bec4    ,creeping of    
mycelia1 #adb4    ,crepis1 #beb4        
,crimson spots1 #ahi4                   
,cross-breeding1 #bff4                  

,cross-fertilisation1 #fi1 #gd1 #gg1    
#bha4    ,cross-graining1 #abd4         
,crucifers1 #bai1 #bhd4    ,cryptogams1 
#hg1 #ajh1 #aaa1 #aac4    ,cuckoo-spit1 
#bcc4    ,cucullate leaves1 #bec4       
,cucumber1 #bai4    ,cucurbitaria1 #bag1
 #bdc4    ,cultivation of pest and host 
plant1 #afh4    ,curculio1 #bdh4        
,curling1 #bce1 #bdf4    ,cuscuta1 #acd4
    ,cuts1 #aai1 #adc1 #aid4            
,cuttings1 #aid1 #aih1 #bfb1 #bfc4      
,cyanide of potassium1 #afe4    ,cycads1
 #abh4    ,cynips1 #aaj1 #bac1 #bai4    
,cystopus1 #aaf1 #acf1 #age1 #ahg1 #bag1
 #bdg1 #beb4    ,cytases1 #acb4         
,cytisus ,adami1 #bfd1 #bhc4     ,daisy1
 #bgh4    ,damping off1 #aad1 #add1     
#afj1 #bbi1 #bhd4    ,dandelion1 #bdg1  
#beb4    ,daniel's researches1 #bhc4    
,dark heat rays1 #bg4    ,darwin1 #gb1  
#abe4    ,dasyscypha ,willkommii1 #aeb1 
#bbc4    ,death1 #bga1 #bgb1 #bhg1 #bij4
    ,de ,bary1 #he1 #aea4    ,deficiency
 of iron1 #ahj4    ,defoliation1 #aji1  
#bdj1 #bdd4    ,deformation1 #acb4      

,dematium1 #ace4    ,dematophora1 #adc1 
#ade4    ,denitrification1 #fb4         
,derivation of ,phytopathology1 #he4    
,destruction1 #bge4    ,development of  
root-hairs1 #dj4    ,dextrine1 #agc4    
,diagnosis1 #he1 #hi4    ,diastases1    
#acb4    ,diffusion1 #ec4    ,digestion1
 #acc4    ,digraphis1 #age4             
,dilophia1 #ahh4    ,dionaea1 #abe4     
,dipsacus1 #beb4    ,diptera1 #bjg4     
,dis-assimilation1 #bge1 #bgg1 #bhf4    
,discolorations1 #agi1 #ahf1 #aib4      
,disease1 #fd1 #ia1 #bga1 #bgb1 #bgg1   
#bhg1 #bhh1 #bij4    ,disease dodging1  
#afh4    ,disease-fungi1 #ahi4          
,disease of organs1 #aai4               
,disease-proof varieties1 #afh1 #afi1   
#aga1 #agc1 #agg4    ,disease-resisting 
varieties1 #agg4    ,diseases of        
absorptive organs1 #aba4    ,diseases of
 assimilatory organs1 #aai4    ,diseases
 of bark1 #abj4    ,diseases of cambium1
 #abj4    ,diseases of parenchyma1 #abj4
    ,diseases of respiratory organs1    
#aai1 #aba4    ,disintegration1 #bge4   

,distortions1 #adj1 #bdf1 #bea1 #beb1   
#bec4    ,dissemination of fungi1 #adb4 
,division1 #abg4    ,dodder1 #aac4      
,dolium1 #acd4    ,dormant buds1 #bbd1  
#bbe1 #beg1 #bei1 #bfj4    ,double      
flowers1 #bdg1 #bef4    ,double ideals  
in selection1 #afh4    ,dracaena1 #aib4 
,drainage1 #ajc4    ,drawing1 #ajf1     
#ahj4    ,drip1 #ajc4    ,drooping1 #dc1
 #agi4    ,drops of water1 #aib4        
,dropsy1 #bbh4    ,drought1 #aba1 #ahc1 
#aij1 #aia1 #bde1 #bdh1 #bdi4           
,dry-rot1 #adc1 #bcg4    ,ducks1 #add4  
,dutrochet1 #g4    ,dwarfing1 #bdf1     
#bdi4    ,dying back1 #aij1 #bdj1 #bdb1 
#bdc1 #bdd4     ,earwigs1 #afd1 #bjg4   
,eau ,celeste1 #afb4    ,edelfaeule1    
#bcj4    ,eelworms1 #aaa1 #bdh4         
,effects of environment1 #bfb4    ,eggs 
of insects1 #ahg4    ,elaborated sap1   
#id4    ,elm1 #bah1 #bbd1 #bbe1 #bcc1   
#bfj4    ,empusa1 #afc4    ,endemic     
diseases1 #aec1 #afj1 #aff4    ,endive1 
#ahj4    ,endophytes1 #acj4             
,endophytic algae1 #abh4    ,endophytic 

fungi1 #aic4    ,energy in plants1 #ae1 
#be1 #bhg4    ,engelmann1 #bj1 #bg4     
,entyloma1 #ahg4    ,enzymes1 #aj1 #acj1
 #acb1 #acf4    ,epichloe1 #bah4        
,epicormic shoots1 #bbd1 #beg1 #bfj4    
,epidemics1 #ajh1 #aji1 #aac1 #aae1     
#adb1 #aec1 #afj1 #afc1 #aff4           
,epiphytes1 #aac1 #acj1 #ace1 #acg4     
,epiphytic algae1 #ahh4    ,epiphytic   
fungi1 #afa1 #aic1 #bcb4    ,equisetum1 
#aac4    ,ergot1 #aca1 #adb1 #add4      
,erineum1 #hh1 #bab1 #bad1 #bae4        
,erosions1 #bjd1 #bjg4    ,erysipheae1  
#ace1 #adb1 #afa1 #ahg1 #bfh4           
,essentials of fertilisation1 #fi4      
,estimates of loss1 #adf4               
,etiolation1 #ajf1 #agi1 #ahj1 #bbi4    
,euphorbia1 #aaf1 #acd1 #bdg1 #bff4     
,excavations1 #bjd4    ,excess of food1 
#bbi4    ,excess of minerals1 #ajb4     
,excess of water1 #ajj4    ,excessive   
growth1 #bdf4    ,excessive nutrition1  
#bej4    ,excrescences1 #aad1 #bab1     
#bbb4    ,excreta1 #de1 #acj1 #acc4     
,exobasidium1 #abh1 #bah4    ,exoascus1 

#aaf1 #abh1 #ahh1 #bjh1 #bad1 #bah1     
#bbe1 #bdg1 #bec4    ,expense of        
materials1 #afa4    ,experiments        
necessary1 #afh4    ,exposure of roots1 
#agi1 #ahd4    ,external causes of      
disease1 #ii4    ,extinction of species1
 #ia4    ,exudations1 #bbg4             
,exudation under pressure1 #ea4         
,factors of an epidemic1 #adi1 #afe4    
,falling of fruit1 #bjf4    ,falling    
leaves1 #abc4    ,false chlorosis1 #aha4
    ,false etiolation1 #ahj4            
,farfugium1 #ahh4    ,fasciations1 #bcj1
 #bdf1 #bea4    ,fats1 #bgb1 #bhf4      
,feeding1 #ad1 #af4    ,fermentation1   
#eh1 #ajb1 #acj1 #bcc4    ,ferns1 #aac1 
#bdg1 #bfj1 #bfa4    ,fertilisation1    
#ga4    ,field-mice1 #afd4    ,figs1    
#aac4    ,finger and toe1 #aad1 #abg1   
#afc4    ,fire1 #bdj4    ,flaming1 #afd4
    ,flattened roots1 #bdf1 #beb4       
,fleshiness1 #bbh4    ,flies1 #hf1 #aaj1
 #adb1 #adc1 #ade4    ,flux1 #bbg1 #bca4
    ,flying foxes1 #bdd4    ,focussing  
of solar rays1 #aib4    ,foliage1 #aaj4 

,fontaria1 #acd4    ,food1 #ah4         
,forest-fires1 #bda4                    
,formic-aldehyde1 #bj4    ,foul         
products1 #ajj4    ,foxy leaves1 #aia4  
,freezing1 #aba1 #ahc4    ,frit fly1    
#ahb4    ,frost1 #aec1 #afj1 #bbe1 #bbi1
 #bdh1 #bdi4    ,frost-beds1 #bdc4      
,frost-blisters1 #bab1 #bah4    ,frost  
canker1 #bbb4    ,frost-cracks1 #bjd1   
#bji1 #bdb4    ,frost-patches1 #bdj4    
,frost-ridge1 #bji4    ,fumago1 #aij1   
#bcb4    ,fumes1 #ajd4    ,functions of 
roots1 #dc1 #de4    ,functional         
depression1 #if4    ,fungi1 #hi1 #ajh1  
#adc1 #agd1 #ahi1 #bjj1 #bje1 #bjg1     
#bjh1 #bab1 #baf1 #bai1 #bbc1           
#bbi1 #bca1 #bcc1 #bch1 #bdj1 #bda1     
#bdc1 #bdh1 #bea1 #bee1 #beh1 #bfe1     
#bfg1       #bhc1 #bhd1 #bhh4    ,fungus
 attacks1 #aci4    ,fungus galls1 #bai4 
,fusarium1 #adc1 #bch4    ,fusicladium1 
#ahi4    ,fusisporium1 #bcg4     ,gagea1
 #beh4    ,gall-apple1 #bah4            
,gall-flies1 #bai4    ,gall-insect1     
#aci4    ,gall-like swellings1 #abh4    

,galls1 #hf1 #aaj1 #abj1 #acj1 #ach1    
#bab1 #bad1 #bah1 #bee4    ,gangrene1   
#bca4    ,garreya1 #bfd4    ,gas1 #afj4 
,gases in soil1 #ajd4    ,gastropacha1  
#bbe4    ,gelatine1 #afc4    ,general   
death1 #aaf4    ,general disease1 #aai1 
#abj4    ,germ-plasm1 #bfg4             
,gesneria1 #bfj4    ,glechoma1 #bah4    
,gloeosporium1 #ahi1 #aij1 #bjh4        
,gloxinia1 #bfj4    ,goats1 #afd4       
,gooseberry1 #bag4    ,graft-hybrids1   
#bfb1 #bfg1 #bga1 #bhc4    ,grafting1   
#gh1 #aee1 #afi1 #ahc1 #bej1 #bfb1 #bga1
 #bha4    ,grain-rust1 #adf4    ,grapes1
 #aib1 #bcj1 #bca4    ,grapholitha1     
#aji1 #bjg4    ,grass1 #aaa1 #ahi1 #aij1
 #bje1 #bah1 #bcc4    ,green fly1 #afa4 
,grew1 #he4    ,greyish spots1 #ahg4    
,growth1 #bga1 #bgd1 #bge1 #bhf4        
,grubs1 #aaj1 #bjg4    ,gumming1 #bce4  
,gummosis1 #bbg1 #bcd1 #bce4            
,gymnosporangium1 #aad1 #agf1 #bbc4     
,hail1 #ajf1 #bdj1 #bda4    ,hales1 #he4
    ,haltica1 #bji4    ,hardy varieties1
 #afh1 #agj1 #agg4    ,haustoria1 #acd1 

#ace1 #acf4    ,healing1 #aid1 #aif4    
,healing by cork1 #abc4    ,health1     
#bgb1 #bhg4    ,health and disease1 #ia1
 #ig1 #bhg4    ,heliotropism1 #abf4     
,hemileia1 #adf1 #afi4    ,heredity1    
#gb1 #bhc4    ,herpotrichia1 #ace1 #aij4
    ,hessian ,fly1 #ahb4    ,heterodora1
 #bai1 #bbj4    ,hieracium1 #aab4       
,history of ,phytopathology1 #he4       
,holdfast of roots1 #db4    ,hollyhock  
disease1 #adc4    ,holly1 #bag4         
,honey dew1 #add1 #bbg1 #bcb1 #bcc4     
,hops1 #afb1 #ahg1 #aia1 #bcb1 #bec4    
,hop-aphis1 #adf4    ,hop-disease1 #aff4
    ,hop mildew1 #afa4    ,hormomyia1   
#bai4    ,hornbeam1 #bbd1 #bcc1 #bdb4   
,horse-radish1 #bfj4    ,host1 #bhd1    
#bhe4    ,hyacinth1 #bca1 #bfa4         
,hyacinth disease1 #adc4    ,hybrids1   
#fi1 #aef1 #bha4    ,hybridisation1 #fi1
 #ge1 #afi1 #bff1 #bha4    ,hydrochloric
 acid1 #aha4    ,hydrogen1 #bgb4        
,hymenomycetes1 #bjf4    ,hypertrophy1  
#aai1 #abg1 #aci1 #bac1 #bae1 #bdg1     
#bff4    ,hypochaeris1 #aab4            

,hypomyces1 #bcg4    ,hyponomeuta1 #bed4
     ,ice1 #ahd1 #bji4                  
,ichneumon-flies1 #afe4    ,icterus1    
#aha4    ,illegitimate unions1 #bfe4    
,immunity1 #aee1 #aef1 #afe1 #afh1 #afi4
    ,impervious subsoil1 #aha4          
,inarching1 #bfi4    ,increase in dry   
weight1 #bc4    ,indian agriculture1    
#agb4    ,indian wheats1 #afh4          
,indispensability of elements1 #bgh4    
,infection1 #bfb1 #bfe1 #bfg4           
,ingredients of protoplasm1 #bgb4       
,insect bites1 #bbe4    ,insect         
diseases1 #ade1 #adf1 #aed1 #ahi4       
,insect punctures1 #hh4    ,insects1    
#hi1 #ih1 #ajh1 #aji1 #abj1 #ach1 #adb1 
#aec1 #agd1 #ahg1 #aid1 #bjc1           
#bje1 #bjf1 #bjg1 #bjh1 #bab1 #bbc1     
#bbi1 #bda1 #bdd1 #bdh1 #bea1 #bed1     
#bee1       #beh1 #bei1 #bfi4           
,insolation1 #ahj1 #bdb4                
,intercellular endophytes1 #acf1 #acg4  
,intercellular mycelium1 #abh4          
,interference1 #ia4    ,internal causes 
of disease1 #ii1 #aja4    ,intracellular

 parasites1 #abg1 #acf4                 
,intramolecular respiration1 #bgg4      
,intumescences1 #bab1 #bae4    ,inulin1 
#aa1 #ag4    ,invertebrata1 #ajh4       
,irritability1 #abe1 #abg4              
,irritation1 #aai1 #aci4    ,isaria1    
#afc4    ,ivy1 #aac1 #afe4     ,japanese
 trees1 #bej4    ,jerusalem ,artichoke1 
#bfd4    ,juncus1 #bai4    ,juniper1    
#aad4     ,kidney bean1 #aib4           
,knauers1 #bbc4    ,knife wounds1 #aid1 
#aie4     ,labour1 #afa4    ,lace-wings1
 #afe4    ,lachnus1 #bbc4               
,lady-birds1 #afd1 #afe4    ,lammas     
shoots1 #beg1 #bei4    ,larch1 #afh1    
#aga4    ,larch disease1 #aae1 #adi1    
#aeb1 #aff1 #aga1 #bbc1 #bda4           
,larvae1 #aaj4    ,lateral wounds1 #acb4
    ,lawns1 #aab4    ,laying of wheat1  
#agi1 #ahj4    ,leaf-curl1 #bcf1 #bec4  
,leaf-diseases1 #aad1 #aai1 #abj1 #bdb4 
,leaf-galls1 #bag1 #bah4    ,leaf-miner1
 #hf1 #aji1 #bjd4    ,leaf perforations1
 #bjh4    ,leaf rolling1 #bad1 #bdf1    
#bed4    ,leaf-spots1 #aad1 #aij4       

,leguminoseae1 #acg1 #bai4    ,lemons1  
#bce4    ,lenticels1 #bag4              
,lepidoptera1 #ahg4    ,leptosphaeria1  
#bdi4    ,lichens1 #acg4    ,liebig1 #d4
    ,life1 #bga1 #bhe1 #bhg4    ,life   
and death1 #bga4    ,light1 #bg1 #ajf4  
,lily disease1 #adc4    ,lime1 #afc1    
#bae1 #bah1 #bcb1 #bec1 #bed1 #bfj1     
#bfi4    ,limes1 #agb4    ,limits of    
variation1 #bhg4    ,linaria1 #beb4     
,liquid antiseptics1 #afj1 #afa1 #afb4  
,living environment1 #ii1 #ajh4         
,local action1 #aad4    ,local disease1 
#aai1 #aba4    ,locusts1 #aji1 #ade1    
#afc1 #afd4    ,longicorns1 #bje4       
,loranthus1 #aac1 #bde1 #bfe4    ,losses
 due to epidemics1 #adb4    ,lowering of
 temperature1 #ajj4    ,lucerne1 #bdi4  
,lurking parasites1 #adb1 #ade4         
,lychnis1 #bcb4    ,lyonetra1 #bjf4     
,lysimachia1 #bag4     ,machine1 plant  
compared to a1 #gi4    ,magnesium1 #bgb4
    ,maize1 #aaf1 #agc1 #bai1 #bfg4     
,majanthemum1 #age4    ,malformations1  
#aaf1 #acj1 #aca1 #bdf1 #bea4    ,mal   

nero1 #aij4    ,mallow1 #beb4           
,malpighi1 #he4    ,mammals1 #adb4      
,man and plants1 #ajh1 #adb1 #adc4      
,manna1 #bbg1 #bce4    ,manna ,ash1     
#bce4    ,maple1 #bei4    ,maximum1     
#bhh4    ,maximum absorption1 #ai4      
,maximum assimilation1 #ai4    ,maximum 
temperature1 #aje4    ,mealy bug1 #afd4 
,melampsora1 #agf4    ,melon1 #bbj4     
,messmates1 #fc4    ,metabolic products1
 #bgd4    ,metabolism1 #bc1 #abg1 #bga4 
,metabolites1 #bgh4    ,metallic        
compounds1 #afb4    ,mice1 #ajh1 #afc4  
,microbes1 #bbg4    ,micro-organisms1   
#ahc4    ,mildew1 #hf1 #afd4            
,millardet1 #afi4    ,mineral salts1    
#aja4    ,miniature trees1 #bej4        
,minimum1 #bhh4    ,minimum temperature1
 #aje4    ,misconceptions1 #ab4         
,mistletoe1 #aac1 #bfe4    ,mites1 #aib1
 #bad1 #bee4    ,mixed species1 #aff4   
,molecular structure of protoplasm1     
#bgc1 #bgd4    ,mongrel forms1 #gd4     
,monilia1 #bag1 #bca4    ,monstrosities1
 #bdf4    ,moraine plants1 #bej4        

,moths1 #aaj1 #ade1 #bjf4    ,moulds1   
#bcj1 #bca1 #bcg1 #bdc4    ,mucor1 #bcj1
 #bca4    ,mulberry1 #bdd4              
,mutilations1 #beb4    ,mycelial        
strands1 #ade4    ,mycelium1 #ahh4      
,mycocecidia1 #bai4    ,mycorrhiza1     
#acg4    ,myrtaceae1 #beh4              
,mytilaspis1 #ahg4     ,natural checks1 
#aei4    ,natural demise1 #ia1 #ic4     
,natural ,grafts1 #bfi4    ,natural     
,selection1 #gb1 #ii1 #afg1 #bhf4       
,natural ,wounds1 #bjd4    ,nature of   
soil1 #eg4    ,necrosis1 #bdj1 #bda1    
#bdc4    ,nectria1 #ade1 #bag1 #bbc1    
#bda1 #bdc1 #bfi4    ,nematodes1 #aaa1  
#acd1 #aci1 #bai1 #bbj4    ,nettle1     
#aaf1 #beb4    ,neurotus1 #bai4    ,new 
formations1 #bee4    ,nitrate1 #bgc4    
,nitrification1 #fb1 #ajb4    ,nitrogen1
 #bgb4    ,nodosities1 #bai4    ,nodules
 on roots1 #fc1 #acg4    ,non-living    
environment1 #ii4    ,notommata1 #adj4  
,nuclear fusion1 #bfg4    ,nuclear      
protoplasm1 #bga1 #bgi1 #bhj1 #bij4     
,nuclear substance1 #ga4                

,nucleo-plasm1 #bhj4    ,nuts1 #bdh4    
,oak1 #aaj1 #ahh1 #bae1 #bah1 #bai1     
#bbc1 #bcc4    ,oak leaf-roller1 #bed4  
,oat1 #agf4    ,occlusion1 #bjj1 #bja1  
#bbb1 #bbc4    ,odours1 #add4           
,oedema1 #bbh4    ,olive1 #bbc4         
,onion1 #bca4    ,oniscus1 #ahb4        
,oospora1 #baf4    ,optimum temperature1
 #aje1 #bhh4    ,orange1 #agc1 #ahg1    
#bce1 #bdg4    ,orange-coloured spots1  
#ahg4    ,orchard trees1 #afc4          
,orchestes1 #bjf4    ,orchids1 #aac1    
#bff4    ,organic acids1 #ej4           
,organisation1 #hi4    ,organised       
structure1 #ac4    ,organisms in soil1  
#fj4    ,orobanche1 #aab4    ,osmosis1  
#bf1 #bi1 #df4    ,osmotic pressures1   
#ah1 #da1 #eb4    ,over-crowding1 #ajd1 
#aaa4    ,over-feeding1 #ajb4           
,over-watering1 #ig4    ,oxalic acid1   
#acd1 #acf4    ,oxidation1 #abd4        
,oxygen1 #ajd1 #bgb4                    
,oxygen-respiration1 #ab1 #fd4          
,pallor1 #agi1 #ahj4    ,palms1 #aib4   
,pangium1 #acd1 #afe4    ,parasites1    

#fa1 #aac1 #aai1 #acj1 #aci1 #agd1 #ahg1
 #bcj1 #bfe1 #bfi1 #bhd4    ,parasitic  
algae1 #ahh1 #bag1 #bai4    ,parasitic  
bacteria1 #afc4    ,parasitic diseases1 
#hh1 #aai1 #aba4    ,parasitic epiphyte1
 #acf4    ,parasitic fungi1 #hg1 #ig4   
,parasitism1 #bfb1 #bfd1 #bfh1 #bga4    
,paris1 #age4    ,paris green1 #afb4    
,parti-coloured leaves1 #aia4           
,parti-coloured spots1 #ahf4    ,pasture
 grasses1 #fi4    ,pathology1 #aba1     
#beg4    ,pathology of cell1 #aai4      
,pathological conditions1 #afh1 #agj1   
#bdf4    ,pea1 #aij1 #aia1 #bjf1 #bjh1  
#bdh1 #bfh4    ,peach1 #agj1 #bec4      
,pear1 #agi1 #ahg1 #ahi1 #aia1 #baf1    
#bah1 #bca1 #bdj1 #bdh1 #bdi1 #bec1     
#beg4    ,pedigree wheats1 #fi4         
,pelargonium1 #aih1 #bec4    ,peloria1  
#beb4    ,penicillium1 #bca4            
,peridermium ,pini1 #bbc1 #bcd4         
,periola1 #bch4    ,permanganate1 #afb4 
,peronospora1 #acf1 #afj1 #age1 #ahg1   
#ahi1 #bjh4    ,petasites1 #ahh4        
,petroleum1 #afb4    ,peziza1 #aae1     

#add1 #aeb4    ,phanerogams1 #ajh1 #aaa4
    ,phellomyces1 #bch4    ,phoma1 #bag1
 #bdc4    ,phosphorus1 #bgb4            
,photo-synthesis1 #aa1 #af4             
,phragmidium1 #ahi4    ,phyllachora1    
#ahi4    ,phyllereum1 #bec4             
,phyllobium1 #bag4    ,phyllosiphon1    
#ahh4    ,phyllosticta1 #ahh1 #bji4     
,phylloxera1 #aaj1 #ade1 #adi1 #aed1    
#aee1 #afc1 #aff1 #agb1 #ahh1 #bai1     
#bbj1 #bfh4    ,physiology1 #a1 #ff1    
#he4    ,physiological diseases1 #aai1  
#aba4    ,phytomyza1 #bjf4              
,phytopathology1 #he4    ,phytophthora1 
#aae1 #acf1 #add1 #aej1 #aea1 #bce1     
#bcf4    ,phytophysa1 #bai4             
,phytoptus1 #ahi1 #bac1 #bad1 #bae1     
#bah1 #bai1 #bec1 #bed4    ,pilea1 #bai4
    ,pilobolus1 #abf1 #adj4    ,pines1  
#ahc1 #bbc1 #bcd1 #bea1 #beb4           
,pine-apple1 #beh4    ,pith flecks1     
#bjd1 #bjg4    ,plant as agent of       
disease1 #ii1 #ajh4    ,plant1          
agricultural chemistry of1 #a4    ,plant
 and its food1 #g4    ,plant and its    

surroundings1 #a4    ,plant1 a machine1 
#a1 #ae4    ,plant1 central object of   
study1 #a4    ,plant1 physiology1 #a4   
,plantago1 #beg4    ,plantain1 #aab1    
#beg4    ,plants1 dying out of1 #ic4    
,plasmodia1 #afc4    ,plasmodiophora1   
#aad1 #abf1 #abg1 #add1 #afc1 #bai1     
#bhd1 #bhe4    ,plasmolysis1 #dg4       
,pleospora1 #bcf4    ,pleotrachelus1    
#abf1 #adj4    ,plum1 #aga1 #ahi1 #aib1 
#bji1 #bad1 #bjf1 #bca1 #bce1 #bdh1     
#bdi1 #bfj4    ,poa1 #beh4              
,pocket-like galls1 #aee1 #bad1 #bah4   
,pocket-plums1 #bad4    ,pockets1 #bec4 
,poison1 #ajb1 #acj1 #acf1 #afc1 #baf4  
,poisonous gases1 #aha1 #bdh4    ,pollen
 grain1 #bhh4    ,pollination1 #bdh1    
#bfb1 #bfe1 #bff1 #bga4    ,polydesmus1 
#bcf4    ,polygonatum1 #age4            
,polygonum1 #beh4    ,polymorphism1     
#agd4    ,polyporei1 #adb4              
,polyporus1 #adc1 #bjf4    ,polystigma1 
#ahi4    ,poplar1 #ahh1 #bjf1 #bae1     
#bah1 #bed4    ,post and epidemics1     
#adb4    ,potassium1 #bgb4    ,potassium

 sulphite1 #afb4    ,potato1 #afb1 #aga1
 #aid1 #bji1 #baf1 #bcf1 #bcg1 #beh4    
,potato-disease1 #aad1 #adc1 #adi1 #aej1
 #aff1 #ahi1 #bjg1 #bce4    ,powders1   
antiseptic1 #aei1 #afj1 #afa4           
,predisposition to disease1 #ih1 #ii1   
#aje1 #afh1 #afi1 #bbi1 #bfb1 #bfh1     
#bgg1       #bgh1 #bhb4    ,preventible 
diseases1 #aei4    ,preventitious buds1 
#bei4    ,prolepsis1 #beg1 #bei4        
,proliferations1 #beg1 #beh4            
,properties of soil1 #eg4               
,prophylactic measures1 #afj4           
,proteids1 #acb1 #ach1 #bgb1 #bgg1 #bhf4
    ,proteolytic enzymes1 #acb4         
,protomyces1 #bag4    ,protoplasmic     
molecules1 #bgf1 #bgh1 #bhf4            
,protoplasm1 #cc1 #da1 #bga1 #bgb1 #bgd1
 #bgf4    ,pruning1 #aje1 #adc1 #aid1   
#bbe1 #bej4    ,prussic acid1 #afc1     
#afe1 #agc4    ,psylla1 #bec4           
,puccinia1 #hh1 #aad1 #afi1 #age1 #agf1 
#ahh1 #ahi1 #bdg1 #beb4    ,puckers1    
#bad1 #bce1 #bdf1 #bec4    ,puffing of  
spores1 #adb1 #add4    ,punctures1 #bab4

    ,pure culture1 #aff4                
,purple-black spots1 #aia4    ,pustules1
 #ahh1 #aij1 #bab1 #bag4                
,putrefaction1 #bcd4    ,pyrethrum1     
#afa4    ,pyrus1 #bad4    ,pythium1     
#aad1 #aai1 #acf1 #add1 #afj1 #bcj4     
,quassia1 #afa4    ,quinine1 #agc4      
,rabbits1 #ajh1 #adb1 #afd1 #aid4       
,rain trees1 #bcc4    ,rankness1 #ig1   
#bbg1 #bbh4    ,rats1 #ajh1 #afc4       
,rays of light1 #ah4    ,red light1 #ba4
    ,red spider1 #afa1 #ahg1 #ahh1 #aib4
    ,red spots1 #ahh1 #bec4             
,references in ,bible1 #he4    ,remedial
 measures1 #hi4    ,repellent           
substances1 #acf4    ,reproduction1 #gb1
 #bha4    ,reserves1 #bgd4    ,resin1   
#abe4    ,resin-flux1 #bcd4             
,resinosis1 #bbg1 #bcd4    ,resistance  
to disease1 #aee1 #bfh4    ,resistant   
races1 #agb4    ,respiration1 #ag1 #ca1 
#acj1 #bga1 #bge1 #bgf1 #bhe1 #bhg4     
,reversions1 #gc4    ,rhinanthoideae1   
#bfe4    ,rhinanthus1 #aab4             
,rhizobium1 #bhi4    ,rhizoctonia1 #bch4

    ,rhizomorph1 #ade4    ,rhododendron1
 #bah4    ,rhubarb1 #ahj1 #bcj4         
,rhynchitis1 #bed4    ,rhytisma1 #ahh4  
,ribbon grass1 #ahc4    ,ribes1 #bad4   
,rice1 #agb4    ,rimpau's experiments1  
#fi1 #gc1 #gg4    ,ringing1 #aid1 #bja1 
#bjb1 #baj4    ,ripened wood1 #bdc4     
,robinia1 #bei4    ,rodents1 #aji4      
,roestelia1 #bag4    ,rolled leaves1    
#hf4    ,root1 #i1 #ce1 #if1 #abj1 #bbg1
 #bgj4    ,root-absorption1 #aha4       
,root-diseases1 #aai1 #abj4             
,root-excretions1 #df4    ,root-fusions1
 #bfb4    ,root-galls1 #bba4            
,root-hairs1 #cd1 #ajb1 #afc4           
,root-nodules1 #bab1 #bai4              
,root-parasites1 #aab1 #bfe4            
,root-rot1 #bcj4    ,roses1 #bcb1 #bdc1 
#beg1 #bfh1 #bgh4    ,rosettes1 #bbe4   
,rot1 #ig1 #ahb1 #bbg1 #bbi1 #bca1 #bcf4
    ,rotation of crops1 #fi1 #aff4      
,rotifer1 #adj4    ,rot-organisms1 #bjj4
    ,rotting of wounds1 #hg4    ,rouen  
law1 #he4    ,rushes1 #aad4    ,rust1   
#abb1 #adb1 #aga1 #agb1 #age1 #aia4     

,rye1 #agf1 #bdh4     ,saccharomyces1   
#fj4    ,sachs1 #g1 #cf4    ,salvia1    
#bad4    ,san ,jose scale1 #ahg4        
,sand-blast action1 #ahd4    ,sandy     
soils1 #ahd4    ,saperda1 #bje4         
,saprophytes1 #ace1 #acg1 #age1 #bcd1   
#bdc1 #bdd4    ,scab1 #ahi1 #baf4       
,scale1 #ahg4    ,schinzia1 #aad4       
,schizoneura1 #bbc4    ,scion1 #ahc1    
#bfb1 #bfd1 #bff1 #bhb4                 
,scleroderris1 #bbc4    ,sclerotia1     
#adc4    ,schwarz1 #ci4    ,sclerotinia1
 #adb1 #adc1 #add1 #bca1 #bdh1 #bdi1    
#bhh4    ,scolytidae1 #bje4             
,scorching1 #bdj1 #bda4    ,scurf1 #baf4
    ,sea-kale1 #bfa4    ,secale1 #gf4   
,secretions1 #acj1 #acc1 #agc1 #bgd4    
,sedges1 #ahi4    ,seedless grapes1     
#bdg4    ,selandria1 #bjh4              
,selection1 #fi1 #gd1 #gh1 #afi4        
,selective absorption1 #ec1 #fe4        
,self-fertilisation1 #bha4              
,semi-parasites1 #aab4    ,senecio1     
#ahh4    ,sensitive plant1 #abe4        
,septoria1 #aad1 #ahg4    ,sewage       

waters1 #ei4    ,sexual act1 #gb4       
,shaded foliage1 #aac4    ,shanking1    
#bdf1 #bdi4    ,shoots from old wood1   
#bfj4    ,shot holes1 #bjd1 #bjh1 #bji4 
,silver fir1 #bbd4    ,silver leaf1     
#aib4    ,sirex1 #bjf4    ,skeleton     
leaves1 #bjd1 #bjg4    ,slime flux1     
#bbg1 #bcc4    ,slime fungus1 #bai4     
,slugs1 #aaa1 #afd1 #bjg1 #bfi4         
,smut1 #aag1 #adc1 #afb1 #aij4          
,snails1 #aaa1 #adb1 #bjg4    ,snow1    
#ajf4    ,soap1 as insecticide1 #afa4   
,soil1 #a1 #db1 #ii1 #ajb1 #adb1 #afc4  
,soil-bacteria1 #fj4                    
,soil-filtration1 #ei4                  
,soil-organisms1 #fa1 #adc4    ,solar   
energy1 #ace4    ,somato-plasm1 #bfg4   
,sooty moulds1 #ace1 #aij1 #bcb4        
,sorbus1 #bjg4    ,sorosporium1 #baf4   
,sour-rot1 #bca4    ,sparrows1 #afd4    
,specialised races1 #afh1 #agf4         
,specific predisposition1 #aee4         
,spectrum1 #ai1 #ba1 #bf4               
,spermogonia1 #add1 #bcb4               
,sphaerella1 #ahi4    ,sphaerotheca1    

#ahg4    ,sphaeroblasts1 #bbb1 #bbe4    
,spicaria1 #bcg4    ,spiral grooving1   
#bjd1 #baj4    ,spiral growth1 #beb4    
,spongospora1 #baf4    ,spontaneous     
variations1 #gh1 #bdf1 #bee4    ,spores1
 #add4    ,sports1 #ic1 #bdg4    ,spots 
on leaves1 #abj1 #ahf4    ,spraying1    
#aei1 #afa1 #afb4    ,spreading of      
disease1 #adb4    ,squirrels1 #ajh4     
,stag-head1 #bdj1 #bdd4    ,starch1 #i1 
#af1 #ag1 #bj1 #bc1 #ach1 #agc4         
,statistics of epidemics1 #adg4         
,steeping1 #afa4    ,stem diseases1     
#abj4    ,stereum1 #bjf4    ,sterility  
of soil1 #fa4    ,stimulation1 #aai4    
,stimuli1 #abf1 #abg1 #aci4    ,stock1  
#bfb1 #bfd1 #bff1 #bhb4    ,stomata1    
#bc4    ,stool-shoots1 #bja1 #bbe1 #bfi4
    ,stool stumps1 #aid1 #bja4          
,strangulations1 #bjd1 #bji4            
,strawberry1 #ahi1 #beg4    ,stripping1 
#aid1 #aig4    ,stroma1 #bag4           
,structure1 #bgd4    ,structure of      
protoplasm1 #bga4    ,structure of      
root-hairs1 #dj4    ,struggle for       

existence1 #aje1 #aei1 #afd1 #afe1 #afg1
 #bhf4    ,study of causes1 #he4        
,stumps1 #aid4    ,subsoil1 #eg1 #ajc4  
,substitutive selections1 #bhf4         
,suckers1 #bbe1 #bfj4    ,sugar1 #aa1   
#ag1 #bj1 #agc1 #bhf4    ,sugar cane1   
#agb4    ,sugar cane disease1 #aff4     
,sulphate1 #bgc4    ,sulphur1 #afa1     
#afc1 #bgb4    ,sulphurous acid1 #aha4  
,sun-burn1 #bdj1 #bda4    ,sun-cracks1  
#bdj1 #bdb4    ,sundew1 #bcb4           
,sunflower1 #bef1 #bfd4    ,sun-spots1  
#aib4    ,superstitions1 #he4           
,surface energy1 #bf4    ,surface roots1
 #aab4    ,sweet almond1 #agc4          
,symbiosis1 #fc1 #acj1 #acg1 #bai1 #bfc1
 #bfe1 #bfh1 #bhe4    ,symptoms of      
disease1 #hi1 #abb1 #agi1 #ahf4         
,synchytrium1 #abg1 #ahh1 #bag1 #bdg4   
,synthesis1 #fe4    ,syringa1 #bei4     
,syringing1 #afa1 #afd4     ,tamarisk1  
#bce4    ,tannin1 #ach4    ,taphrina1   
#bah4    ,tar1 #afd4    ,tea1 #bdd4     
,teazel1 #beb4    ,teleutospore1 #ahi1  
#aia4    ,temperature1 #ii1 #aje4       

,tendencies to ill-health1 #ia4         
,tendrils1 #abe4    ,teratology1 #bdf1  
#bec1 #bed1 #beg4    ,tetraneura1 #bah4 
,tetranychus1 #ahg1 #aib4    ,thawing1  
#ahc4    ,thelephora1 #bjf4             
,therapeutics1 #he1 #hi1 #aei4          
,thermotropism1 #abf4    ,thesium1 #aab4
    ,thick-skinned organs1 #afh1 #aga4  
,thinning1 #if1 #aje4    ,thistle1 #bdg4
    ,thrips1 #hh1 #aia1 #bjh4           
,thyloses1 #abe4    ,tilia1 #bad4       
,timber diseases1 #aai1 #abj4           
,timiriazeff1 #ba4    ,tinea1 #bjf4     
,tissue diseases1 #aai4    ,tobacco1    
#bji4    ,tobacco powder1 #afa4         
,tomato1 #aga1 #bai1 #bcj4    ,top-dry  
trees1 #bdd4    ,topical remedies1 #afa4
    ,tomicus1 #bje4    ,torsions1 #bdf1 
#beb4    ,tortrix1 #bed4    ,toxic      
agents1 #acj4    ,transformation of     
energy1 #be1 #bh4    ,transformation of 
organs1 #bed1 #bee4    ,transmission of 
acquired characters1 #bfd1 #bhc1 #bij4  
,transplanting1 #if4    ,transpiration1 
#aha1 #bbh4    ,trees1 #aji4            

,trichosphaeria1 #ace4    ,triticum1    
#gf4    ,tumescence1 #bbg1 #bbh4        
,tunnels1 #bjf4    ,turgescence1 #dg1   
#bbh1 #bcj4    ,turnip1 #abf1 #afb1     
#bcj4    ,twitch1 #aac4    ,tylenchus1  
#bch1 #bdh4     ,ulcer1 #bca4    ,unger1
 #he4    ,unsuitable soils1 #aja4       
,upheaval of seedlings1 #agi1 #ahc4     
,uredineae1 #aad1 #acd1 #acf1 #ade1     
#afi1 #ahh1 #ahi4    ,uredo1 #hh1 #ahh1 
#aia4    ,uredospores1 #aia4            
,uromyces1 #aaf1 #ahh1 #aia1 #bff4      
,urocystis1 #bbj4    ,ustilagineae1     
#ade1 #aij1 #bag1 #bdh4    ,ustilago1   
#aaf1 #aag1 #age1 #aij1 #bai1 #bee4     
,vaccinium1 #abh1 #bhh4    ,variability1
 #agd4    ,variation1 #fg1 #gb1 #ia1    
#ib1 #afh1 #agd1 #agf1 #bdf1 #bfb1 #bfc1
 #bfd1 #bga1       #bhb1 #bhf1 #bhh1    
#bhi4    ,variegation1 #agi1 #ahb1 #ahc1
 #aib4    ,varieties1 #gh1 #bdg4        
,varieties of soil1 #ef4    ,vaucheria1 
#aci1 #adj4    ,vegetable acids1 #dh4   
,vertebrata1 #ajh4    ,verticillium1    
#ade1 #bcf4    ,viburnum1 #bad4         

,vine1 #aaj1 #adi1 #aef1 #afb1 #afd1    
#afi1 #aga1 #ahi1 #aij1 #aia1 #bbb1     
#bdh1 #bfh4    ,vine disease1 #adc4     
,vivipary1 #beg1 #beh4     ,walnut1     
#aij1 #bji1 #bec4    ,want of air1 #ajj4
    ,washing leaves1 etc41 #afa4        
,wasp-flies1 #afe4    ,wasps1 #ade4     
,water1 #bgb4    ,water and insects1    
#afa4    ,water-culture1 #fe4    ,water 
in soil1 #ajc4    ,waterlogging1 #aha4  
,weaving of fungi1 #aij4    ,webs1 #aij1
 #bed4    ,weeding1 #aje4    ,weeds1    
#fi1 #aaa1 #aac1 #afe1 #bbi1 #bdi4      
,weevils1 #bdh4    ,wet feet1 #aha4     
,wheat1 #afi1 #aga1 #agb1 #agf1 #agi1   
#ahj1 #ahb1 #ahc1 #bcj1 #bdh4    ,wheat 
rust1 #hf1 #abb1 #adf1 #aff1 #afi1 #agf4
    ,white spots1 #ahf1 #ahg4           
,willow1 #bjf1 #bjg1 #bai1 #bbc1 #bcc1  
#bei4    ,willow beetle1 #bjh4          
,wilting1 #agi1 #aha1 #bce1 #bdi4       
,wind1 #ajf1 #adb1 #add1 #aec1 #ahd1    
#bji1 #bbi4    ,wire-worms1 #aji1 #aha4 
,witches' brooms1 #aaf1 #bbb1 #bbd4     
,wood1 #abd4    ,wood-ashes1 #afa4      

,woodbine1 #aab1 #baj4    ,wood-boring1 
#bjd1 #bje4    ,woodlice1 #afd4         
,wood-nodules1 #bbe4    ,wood-wasps1    
#bjf4    ,woolly-aphis1 #bai1 #bbc4     
,worms1 #aji1 #adb1 #add1 #aid1 #bch4   
,wounds1 #ajh1 #aci1 #aid1 #bjd1 #bjg1  
#bac1 #bfj1 #bfc1 #bfi4    ,wound-cork1 
#aie4    ,wound-fever1 #abc4            
,wound-fungi1 #bjc1 #bjd1 #bdj4         
,wound-gum1 #abe4    ,wound-wood1 #abd4 
,wrens1 #afe4    ,wrinkling1 #bec4      
,xenia1 #bfg4    ,xyloma1 #hh4          
,yeasts1 #acd1 #agb1 #bca1 #bcc4        
,yellowing1 #agi1 #aha1 #ahb1 #ahd4     
,yellow leaves1 #hi4    ,yellow spots1  
#ahf1 #ahg1 #ahh1 #bec4     ,zoospores1 
#aea4   ,,glasgow3 ,,printed ,,at ,,the 
,,university ,,press ,,by ,,robert      
,,maclehose ,,and ,,co4     ,,macmillan 
,,and ,,co4',s ,,works ,,on ,,botany4   
,,by ,,the ,,same ,,author4  ,crown     
#hvo4 ,price #fs4   ,timber and ,some of
 its ,diseases4       ,by ,h4 ,,marshall
 ,,ward1 ,d4,sc41 ,f4,r4,s41 ,f4,l4,s41 
,fellow of ,sidney      ,sussex         

,college1 and ,professor of ,botany in  
the ,university of      ,cambridge4     
,illustrated4            ,,manchester   
,,examiner4--,the subject as a whole is 
one which is little understood in       
,england1 and           ,professor      
,marshall ,ward's work cannot fail to be
           useful4 ,the student will be 
much helped by the           numerous   
illustrations4            ,,gardener',s 
,,chronicle4--,this is a book whose     
appearance we hail with great           
satisfaction4 4 4 4 ,we                 
heartily recommend its perusal to those 
concerned4       ,the ,study of the     
,biology of ,ferns by the ,collodion    
,method4 ,for      ,advanced and        
,collegiate ,students4 ,by ,,george ,f4 
,,atkinson1      ,ph4,b41 ,associate    
,professor of ,cryptogamic ,botany in   
,cornell      ,university4 #hvo4 #hs4   
#f;d4 net4       ,on ,british ,wild     
,flowers considered in ,relation to     
,insects4 ,by      ,,lord ,,avebury1    
,f4,r4,s41 ,d4,c4,l41 ,,ll4,d4          

,illustrated4 ,cr4 #hvo4 #ds4      #f;d4
       ,flowers1 ,fruits1 and ,leaves4  
,with illustrations4 ,by ,,lord         
,,avebury1 ,f4,r4,s41 ,d4,c4,l41        
,,ll4,d4 ,cr4 #hvo4 #ds4 #f;d4          
,lessons with ,plants4 ,by ,prof4 ,l4   
,h4 ,,bailey4 ,cr4 #hvo4 #gs4 #f;d4     
,first ,lessons with ,plants4 ,by ,prof4
 ,l4 ,h4 ,,bailey4 ,cr4 #hvo4 #bs4      
#f;d4       ,botany4 ,an ,elementary    
,text ,book for ,schools4 ,by ,prof4 ,l4
 ,h4      ,,bailey4 ,ex4 cr4 #hvo4 #fs4 
,first ,lessons in ,practical ,botany4  
,by ,g4 ,t4 ,,bettany4 ,pott #hvo4      
#as4       ,a ,course of ,practical     
,instruction in ,botany4 ,by ,f4 ,o4    
,,bower1      ,d4,sc41 ,f4,l4,s41       
,regius ,professor of ,botany in the    
,university of      ,glasgow4 ,cr4 #hvo4
 #ajs4 #f;d4       ,practical ,botany   
for ,beginners4 ,by ,f4 ,o4 ,,bower1    
,d4,sc41 ,f4,l4,s4      ,gl4 #hvo4 #cs4 
#f;d4       ,lectures on the ,evolution 
of ,plants4 ,by ,,douglas ,,houghton    
,,campbell1 ,ph4,d41 ,professor of      

,botany in the ,leland ,stanford        
,junr4 ,university4 ,cr4 #hvo4 #ds4     
#f;d4 net4       ,botany for ,beginners4
 ,by ,,ernest ,,evans1 ,burnley         
,technical      ,school4 ,globe #hvo4   
#bs4 #f;d4       ,the ,teaching         
,botanist4 ,a ,manual of ,information   
upon ,botanical      ,teaching1 with an 
outline for a general course4 ,by       
,,william ,f4      ,,ganong1 ,professor 
of ,botany in ,smith ,college4 ,cr4     
#hvo4 #es4       ,structural ,botany2   
or1 ,organography on the ,basis of      
,morphology4 ,to which is added the     
,principles of ,taxonomy and            
,phytography1 and a ,glossary of        
,botanical ,terms4 ,by ,,asa ,,gray1    
,,ll4,d41 ,fisher ,professor of ,natural
 ,history 7,botany7 in ,harvard         
,university4 #hvo4 #ajs4 #f;d4          
,text-,book of the ,diseases of ,trees4 
,by ,prof4 ,r4 ,,hartig of the          
,university of ,munich4 ,trans4 by      
,prof4 ,,wm4 ,,somerville1 ,f4,r4,s41   
,f4,l4,s41 ,professor of ,agriculture   

and ,forestry1 ,durham ,college      of 
,science1 ,newcastle-on-,tyne4          
,introduction by ,prof4 ,h4             
,,marshall ,,ward1 ,d4,sc41 ,f4,r4,s41  
,f4,l4,s41 ,professor of ,botany at     
the ,royal ,indian ,engineering         
,college1 ,cooper's ,hill4 ,with        
numerous illustrations4 #hvo4 #ajs4 net4
       ,the ,student's ,flora of the    
,british ,isles4 ,by ,sir ,j4 ,d4       
,,hooker1      ,m4,d41 ,d4,c4,l41       
,,ll4,d41 ,f4,r4,s4 ,third edition4     
,globe #hvo4 #ajs4 #f;d4       ,a       
,primer of ,botany4 ,by the same4 ,pott 
#hvo4 #as4       ,timber and ,timber    
,trees1 ,native and ,foreign4 ,by       
,,thomas      ,,laslett4 ,second        
edition4 ,revised by ,h4 ,,marshall     
,,ward1 ,f4,r4,s4      ,cr4 #hvo4 #hs4  
#f;d4       ,the ,yew ,trees of ,great  
,britain and ,ireland4 ,by ,,john       
,,lowe1      ,m4,d41 ,honorary          
,physician to ,his ,royal ,highness the 
,prince of      ,wales2 ,fellow of the  
,linnean ,society2 ,fellow of the       

,botanical      ,society of ,edinburgh4 
,illustrated4 #hvo4 #ajs4 net4          
,the ,nature and ,work of ,plants4 ,an  
,introduction to the ,study of          
,botany4 ,by ,d4 ,t4 ,,macdougal1       
,ph4,d4 ,crown #hvo4 #ds4 #f;d4         
,introduction to ,study of ,seaweeds4   
,by ,g4 ,,murray4 ,cr4 #hvo4 #gs4       
#f;d4       ,british ,forest ,trees and 
their ,sylvicultural ,characteristics   
and ,treatment4 ,by ,j4 ,,nisbet4 ,cr4  
#hvo4 #fs4 net4       ,lessons in       
,elementary ,botany4 ,the ,part on      
,systematic ,botany      based upon     
material left in manuscript by the late 
,professor      ,henslow4 ,by ,,daniel  
,,oliver1 ,f4,r4,s41 ,f4,l4,s41 formerly
 ,keeper of      the ,herbarium and     
,library of the ,royal ,gardens1 ,kew1  
and      ,professor of ,botany in       
,university ,college1 ,london4          
,illustrated4 ,fcap4 #hvo4 #ds4 #f;d4   
,first ,book of ,indian ,botany4 ,by    
,,daniel ,,oliver1 ,f4,r4,s41 ,f4,l4,s4 
,illustrated4 ,ex4 fcap4 #hvo4 #fs4     

#f;d4       ,laboratory ,practice for   
,beginners in ,botany4 ,by ,,william ,a4
      ,,setchell1 ,ph4,d41 ,professor of
 ,botany in the ,university of          
,california4 ,fcap4 #hvo4 #ds4 #f;d4    
net4       ,economic ,plants1           
,dictionary of ,popular ,names of2      
,their      ,history1 ,products1 and    
,uses4 ,by ,j4 ,,smith4 #hvo4 #ads4     
,a ,text-,book of ,botany4 ,by ,dr4 ,e4 
,,strasburger1 ,dr4 ,,fritz ,,noll1     
,dr4 ,h4 ,,schenck1 ,dr4 ,a4 ,f4 ,w4    
,,schimper4 ,translated from the        
,german by ,h4 ,c4 ,,porter1 ,ph4,d41   
,assistant ,instructor of ,botany1      
,university of ,pennsylvania4 ,revised  
and ,edited by ,a4 ,c4      ,,seward4   
,with #eid illustrations1 in part       
coloured4 ,medium #hvo4      #ahs4 net4 
,the ,herb of the ,field4 ,by           
,,charlotte ,m4 ,,yonge4 ,new edition1  
revised4 ,cr4 #hvo4 #es4   ,,macmillan  
,,and ,,co41 ,,ltd41 ,,london4          
,transcriber's ,notes3   ,the word      
,oedema uses an ,,oe ligature in the    

original4  ,the following corrections   
have been made to the text3       ,page 
vi3 be the better for a real            
knowledgeoriginal has      knowlege     
,page #ee3 andoriginal has and and are  
too crudely mechanical       ,page #aag3
 ,prillieuxoriginal has ,prilleux1      
,maladies des      ,plantes ,agricoles  
,page #abh3 the intercellular mycelium  
of ,exoascusoriginal      has ,exoacus  
,page #acd3 subject to attacks of       
,uredineaeoriginal has      ,uredinae   
,page #adb3 carriedoriginal has carrried
 from plant to plant       ,page #agf3  
its aecidiaoriginal has aecida on the   
,barberry       ,page #ahb3 e4g4        
,oniscusoriginal has ,oscinis1 the ,frit
      ,fly1 and ,cecidomyiaoriginal has 
,cecidomya       ,page #ahb3 not        
necessarily less ash                    
constituentsoriginal has                
constitutents       ,page #ahc3 nature  
of a transmissible enzymeoriginal has   
enyzme       ,page #bjc3 ,krankh4 d4    
,pflanzen1 ,b4 ,i4original has #a cap4  

#b       ,page #bjf3 leaves of ,apples  
by ,lyonetiaoriginal has      ,lyonettia
       ,page #bah3 ,epichloeoriginal has
 ,epichloe1 which clothes the           
sheaths       ,page #bai3 beetle which  
attacks ,crucifersoriginal has          
,crucificers       ,page #bba3 on the   
green parts of ,hibiscus1comma missing  
in      original       ,page #bba3      
nodules of the roots of                 
,leguminoseaeoriginal has               
,leguminosae       ,page #bcj3          
,edelfaeuleoriginal has ,edelfauele1 a  
rotten      condition of the grapes     
,page #bce3 giving an almost            
mealyoriginal has meally      appearance
       ,page #bdc3 as its               
myceliumoriginal has myceliun spreads   
,page #beh3 ,prolepsis4original has     
,proplesis--,it frequently       ,page  
#bic3 ,aetiologyoriginal has            
,a,etiology1 #hi1 #ajj4       ,page     
#bic3 ,anthonomusoriginal has           
,anthonomos1 #bdi4       ,page #bid3    
,bird's-eyeoriginal has ,birds'-eye     

,maple1 #bbd4       ,page #bie3         
,cercospora1original has ,cereospora    
#aij4       ,page #bih3 ,eau            
,celesteoriginal has ,celeste1 #afb4    
,page #cjj3 ,heterodoraoriginal has     
,heterodera1 #bai1 #bbj4       ,page    
#cjj3 ,holly1 #bag4period missing in    
original       ,page #cjj3 ,hypomyces1  
#bcg4original has comma       ,page     
#cja3 ,lyonetiaoriginal has ,lyonetra1  
#bjf4       ,page #cjc3                 
,permanganateoriginal has ,permangate1  
#afb4       ,page #cjd3                 
,prophylacticoriginal has ,phophylactic 
measures1      #afj4       ,page #cjd3  
,phytomyza1 #bjf4period missing in      
original       ,page #cjd3              
,phyllereumoriginal has ,phyllereus1    
#bec4       ,page #cjd3                 
,pine-appleoriginal has ,pine apple1    
#beh4       ,page #cje3 ,puccinia1 #hh1 
#aad1 #afi1 #age1 #agf1 #ahh1 #ahi1     
#bdg1      #beboriginal has #beb1 #bdg4 
,page #cjg3 ,somato-plasmoriginal has   
,somatoplasm1 #bfg4       ,page #cjg3   

,spermogoniaoriginal has ,spermagonia1  
#add1 #bcb4       ,page #cjh3           
,tomicusoriginal has ,tornicus1 #bje4   
,the following index entries were out of
 alphabetical order and have been moved 
to the appropriate locations3           
,phylloxera      ,plants1 dying out of  
,poisonous gases      ,preventible      
diseases      ,prophylactic measures    
,spermogonia