,transcriber's ,notes ,text printed in italics has been transcribed between underscores2 underlined text between tildes4 x and x represent a superscript and subscript x respectively4 ,uppercase letters between square brackets 7such as ,a7 refer to footnotes 7to be found directly underneath the paragraph or table71 numbers between square brackets 7such as #a or #a;a refer to references at the end of the chapter7s7 by the same author4 ,more ,transcriber's ,notes may be found at the end of this text4 ,,the ,,rothamsted ,,monographs ,,on ,,agricultural ,,science ,,edited ,,by ,,sir ,e4 ,j4 ,,russell1 ,d4,sc4 7,,lond471 ,f4,r4,s4 ,,the ,,micro-,,organisms ,,of ,,the ,,soil ,,the ,,rothamsted ,,monographs ,,on ,,agricultural ,,science4 ,,edited ,,by ,,sir ,e4 ,,john ,,russell1 ,d4,sc41 ,f4,r4,s4 ,during the past ten years there have been marked developments in knowledge of the relations between the soil and the growing plant4 ,the subject involves physical1 biological1 and chemical considerations1 and its ramifications are now so wide that they cannot be satisfactorily dealt with in detail in any one book4 ,these monographs collectively cover the whole ground4 ,in 8,soil ,conditions and ,plant ,growth0 the general outlines are presented3 in the monographs the various divisions are fully and critically dealt with by the ,heads of the ,departments concerned at ,rothamsted4 ,a homogeneous treatment is thus secured that will1 it is hoped1 much facilitate the use of the series4 ,,soil ,,conditions ,,and ,,plant ,,growth1 ,fourth ,edition4 ,by ,,sir ,e4 ,,john ,,russell1 ,f4,r4,s4 #afs4 net4 ,the following volumes are in preparation3-- ,,manuring ,,of ,,grass-,,lands ,,for ,,hay ,by ,,winifred ,e4 ,,brenchley1 ,d4,sc41 ,f4,z4,s4 ,,the ,,micro-,,organisms ,,of ,,the ,,soil ,by ,sir ,e4 ,,john ,,russell1 ,f4,r4,s41 and ,members of the ,biological ,staff of the ,rothamsted ,experimental ,station4 ,,soil ,,physics ,by ,b4 ,a4 ,,keen1 ,b4,sc4 ,,soil ,,protozoa ,by ,d4 ,w4 ,,cutler1 ,m4,a41 and ,l4 ,m4 ,,crump1 ,m4,sc4 ,,soil ,,bacteria ,by ,h4 ,g4 ,,thornton1 ,m4,a4 ,,soil ,,fungi ,,and ,,alg ,by ,w4 ,b4 ,,brierley1 ,s4 ,t4 ,,jewson1 ,b4,sc41 and ,b4 ,m4 ,,roach 7,bristol71 ,d4,sc4 ,,chemical ,,changes ,,in ,,the ,,soil ,by ,h4 ,j4 ,,page1 ,b4,sc4 ,,longmans1 ,,green ,,and ,,co41 ,,london1 ,,new ,,york1 ,,toronto1 ,,bombay1 ,,calcutta1 ,,and ,,madras4 ,,the ,,micro-,,organisms ,,of ,,the ,,soil ,,by ,,sir ,e4 ,,john ,,russell1 ,f4,r4,s4 ,,and ,,members ,,of ,,the ,,biological ,,staff ,,of ,,the ,,rothamsted ,,experimental ,,station ,,with ,,diagrams ,,longmans1 ,,green ,,and ,,co4 #ci ,,paternoster ,,row1 ,,london1 ,e4,c4 #d ,,new ,,york1 ,,toronto ,,bombay1 ,,calcutta and ,,madras #aibc ,made in ,great ,britain ,,introduction4 ,the purpose of this volume is to give the broad outlines of our present knowledge of the relationships of the population of living organisms in the soil to one another and to the surface vegetation4 ,it is shown that there is a close relationship with vegetation1 the soil population being dependent almost entirely on the growing plant for energy material1 while the plant is equally dependent on the activities of the soil population for removing the residues of previous generations of plants and for the continued production in the soil of simple materials1 such as nitrates1 which are necessary to its growth4 ,it is also shown1 however1 that the soil population takes toll of the plant nutrients and that some of its members may directly injure the growing plant4 ,the soil population is so complex that it manifestly cannot be dealt with as a whole in any detail by any one person1 and at the same time it plays so important a part in the soil economy that it must be seriously studied4 ,team work therefore becomes indispensable1 and fortunately this has been rendered possible at ,rothamsted4 ,each group of organisms is here dealt with by the person primarily responsible for that particular section of the work4 ,the plan of the book has been carefully discussed by all the authors1 and the subject matter has already been presented in a course of lectures given at ,university ,college1 ,london1 under the auspices of the ,botanical ,board of ,studies of the ,london ,university4 ,the interest shown in these lectures leads us to hope that the subject may appeal to a wider public1 and above all to some of the younger investigators in biological science4 ,they will find it bristling with big scientific problems1 and those who pursue it have the satisfaction1 which increases as the years pass by1 of knowing that their work is not only of interest to themselves1 but of great importance in ministering to the intellectual and material needs of the whole community4 ,,contents4 ,,chap4 ,,page ,i4 ,,development ,,of ,,the ,,idea ,,of ,a ,,soil ,,population #a ,sir ,e4 ,,john ,,russell1 ,f4,r4,s41 ,director4 ,,ii4 ,,occurrence ,,of ,,bacteria ,,in ,,soil--,,activities ,,connected ,,with ,,the ,,acquirement ,,of ,,energy #bj ,h4 ,g4 ,,thornton1 ,b4,a41 ,head of the ,department of ,bacteriology4 ,,iii4 ,,conditions ,,affecting ,,bacterial ,,activities ,,in ,,the ,,soil--,,activities ,,connected ,,with ,,the ,,intake ,,of ,,protein ,,building ,,materials #ci ,h4 ,g4 ,,thornton1 ,b4,a41 ,head of the ,department of ,bacteriology4 ,,iv4 ,,protozoa ,,of ,,the ,,soil1 ,i4 #ff ,d4 ,w4 ,,cutler1 ,m4,a41 ,head of the ,department of ,protozoology4 ,v4 ,,protozoa ,,of ,,the ,,soil1 ,,ii4 #gg ,d4 ,w4 ,,cutler1 ,m4,a41 ,head of the ,department of ,protozoology4 ,,vi4 ,,soil ,,alg #ii ,b4 ,,muriel ,,bristol1 ,d4,sc41 ,algologist4 ,,vii4 ,,soil ,,fungi--,,the ,,occurrence ,,of ,,fungi ,,in ,,the ,,soil #aah ,w4 ,b4 ,,brierley1 ,d4,sc41 ,head of the ,department of ,mycology4 ,,viii4 ,,soil ,,fungi--,,the ,,life ,,of ,,fungi ,,in ,,the ,,soil #aca ,w4 ,b4 ,,brierley1 ,d4,sc41 ,head of the ,department of ,mycology4 ,,ix4 ,,the ,,invertebrate ,,fauna ,,of ,,the ,,soil 7,,other ,,than ,,protozoa7 #adg ,a4 ,d4 ,,imms1 ,d4,sc41 ,head of the ,department of ,entomology4 ,x4 ,,the ,,chemical ,,activities ,,of ,,the ,,soil ,,population ,,and ,,their ,,relation ,,to ,,the ,,growing ,,plant #afd ,sir ,e4 ,,john ,,russell1 ,f4,r4,s41 ,director4 ,,index #aha ,,chapter ,i4 ,,the ,,development ,,of ,,the ,,idea ,,of ,a ,,soil ,,population4 ,from the earliest times agriculturists have been familiar with the idea that decomposition of vegetable and animal matter takes place in the soil1 and that the process is intimately connected with soil fertility4 ,by the middle of the nineteenth century three different ways were known in which the decomposition occurred4 ,one had been since early times specially associated with soil fertility1 in that it gave rise to humus1 the black sticky substance in farmyard manure or in soil--which was supposed up to #ahdj to be the special food of plants4 ,no good account of the process or of the conditions in which it occurred is1 however1 given by the older writers4 ,a second resulted in the formation of nitrates4 ,this process became known as nitrification3 it was described by ,georgius ,agricola 7#adid-aeee7 in his book 8,de ,re ,metallica10 and it was of great importance in the seventeenth and eighteenth centuries1 because it was used for the manufacture of gunpowder in the great wars of that period4 ,the conditions for the making of successful nitre beds were so thoroughly investigated that little fresh knowledge was added to that of #aggj;,a until quite recently4 ,this process1 however1 was not usually associated with soil fertility1 although both ,glauber 7#afef7 and ,mayow 7#afgd7 had insisted on the connection4 ,a ,see the remarkable collection of papers entitled 8,instructions sur l'tablissement des nitrires10 publi par les ,rgisseurs-gnraux des ,poudres et ,salptre4 ,paris1 #aggg4 ,a third type of decomposition was brought into prominence by ,liebig in #ahdj4g;,b ,reviewing the decomposition of organic matter in the light of the newer chemistry1 he concluded that the process was a slow chemical oxidation1 to which he gave the name 8,eremacausis40 ,he recognised that humus was formed1 but he regarded it only as an intermediate product1 and emphatically denied its importance in soil fertility4 ,the true fertility agents1 in his view1 were the final products--,,co1 potassium and other alkaline salts1 phosphates1 silicates1 etc4 ,he went on to argue brilliantly that instead of applying farmyard or similar manures to the soil it was altogether quicker and better to apply these mineral compounds obtained from other sources than to wait for the slow process of liberation as the result of decomposition4 ,for some reason1 difficult to understand1 he overlooked nitrification and the part that nitrates might play in soil fertility4 ,lawes and ,gilbert#f were much attracted by this new idea2 they showed that it was incomplete because it took no account of the necessity for supplying nitrogen compounds to the crop4 ,when ammonium salts were added to ,liebig's ash constituents the resulting mixture had almost as good a fertilising effect as farmyard manure4 ,lawes at once saw the enormous practical importance of this discovery1 and set up a factory for the manufacture of artificial fertilisers4 ,he did not1 however1 follow it up more closely on the scientific side4 ,b ,the numbers refer to the short bibliography on p4 #ah4 ,both ,lawes and ,gilbert were in constant touch with the idea of decomposition in the soil1 and they attached so much importance to nitrogen compounds in plant nutrition that it is not easy to understand how they missed the connection with nitrification4 ,but they did so1 and like other ,english and ,german workers of the day1 considered that plant roots assimilated their nitrogen as ammonia4 ,for the first ten years of the history of ,rothamsted only few experiments with nitrates were made1 and not till thirty-five years had elapsed were they systematically studied4 ,it was by ,boussingault#b and in ,france that the connection between nitrification and soil fertility was first recognised4 ,the news came to ,england1 but it was not accepted1 although ,way1 one of the most brilliant agricultural chemists of his time1 showed that nitrates were formed in soils to which nitrogenous fertilisers were added1 and that they were comparable in their fertiliser effects with ammonium salts4#ab 8,the ,french chemists10 he wrote in #ahef1 8are going further1 several of them now advocating the view that it is in the form of nitric acid that plants make use of compounds of nitrogen4 ,with this view ,i do not at present coincide1 and it is sufficient here to admit that nitric acid in the form of nitrates has at least a very high value as manure40 ,indeed1 ,kuhlmann went so far as to argue that the nitrates found in the soil were there reduced to ammonia before assimilation by plants could take place4 ,the water-culture work of the plant physiologists of the 'sixties finally showed the correctness of the ,french view4 ,even when the importance of nitrification was realised its mechanism was not understood3 some thought it was chemical1 some physical4 ,again the explanation came from ,france4 ,pasteur in #ahfb had expressed the view that nitrification would probably be a biological action1 since purely chemical oxidation of organic matter was of very limited occurrence4 8,pntrs de ces ides10 as ,schloesing tells us1 he and ,mntz in a memorable investigation cleared up the whole problem1 and in #ahgg opened the way to a most fruitful field of research4#aj ,the formal description is given in his papers in the 8,comptes ,rendus10 but a more lively account is given in his lectures before the cole d'application des ,manufacteurs de l'tat1 which1 though not printed1 were collected and issued in script by his distinguished son1 and a copy of this work is among the treasures of the ,rothamsted ,library4 ,he had been asked to study the purification of sewage1 and he and ,mntz showed that it was bound up with nitrification4 ,the process was slow in starting1 then it proceeded rapidly4 ,why1 they asked1 was the delay8 ,there should be none if the process were physical or chemical1 and the fact that it occurred strongly suggested biological action4 ,the process was stopped by chloroform vapour1 but could be restarted after the removal of the vapour by the addition of a little fresh soil4 ,the importance of this work in connection with soil fertility was immediately realised by ,warington1 who had recently come to ,rothamsted4#aa ,he quickly confirmed the result1 and made the valuable discovery that two stages were involved--the conversion of ammonia to a nitrite by one organism1 and of the nitrite to nitrate by another4 ,he made long and persistent attempts to isolate the organisms from the soil1 using the best technique of his time1 but though he found many bacteria none of them could nitrify ammonium salts2 yet the soil did it easily4 ,for years he continued his efforts to find the nitrifying organism1 but always failed4 ,his health was not good1 his life at ,rothamsted was not happy owing to disagreements with ,gilbert1 and although his other research work was succeeding1 this investigation on which he had set his heart was not coming out2 bacterial technique was not yet sufficiently far advanced4 ,ten bitter1 disappointing years passed1 and the crown of disappointment came when ,winogradsky1 a young bacteriologist in ,paris1 changed the technique and succeeded at once in isolating both the nitrite and the nitrate-forming organisms4#ac ,the numerous bacteria found by ,warington in the soil suggested the presence of a soil population1 and this idea was greatly strengthened by another line of investigation which was being followed up in ,france4 ,boussingault had shown that soils absorb oxygen and give out carbon dioxide2 ,schloesing extended this discovery1 as also did ,wollny4 ,it was concluded that oxidation was the result of the activities of the soil organisms in decomposing the organic matter of the soil1 and thus preparing the way for the nitrifying organisms4 ,a third important function of soil bacteria was revealed by ,berthelot4#a ,it was known that considerable loss of nitrogen from the soil took place as the result of the conversion of nitrogen compounds into nitrates1 which were subsequently washed out in the drainage water4 ,it followed inevitably that the stock of nitrogen compounds in the soil must long ago have become exhausted had there been no addition of nitrogen compounds to the soil4 ,berthelot argued that there must be fixation of atmospheric nitrogen1 and1 following the prevailing trend of thought in ,france1 he attributed it to bacteria4 ,he confirmed the anticipation by exposing soil to air in such conditions that dust1 rain1 etc41 were excluded1 and he found an increase in the percentage of nitrogen4 ,looking back over the work1 it is difficult to understand the result4 ,the fixation of nitrogen is a process that absorbs energy1 and should have necessitated some source of energy1 which apparently was not supplied4 ,but in spite of this drawback the investigation was immediately fruitful in that it gave the key to another problem which had long puzzled agriculturists4 ,it had long been known that the growth of leguminous crops1 unlike that of others1 enriched the ground1,c and ,lawes and ,gilbert had shown that this was due to an increase of soil nitrogen4 ,but no explanation could be found till ,hellriegel and ,wilfarth solved the problem4#d ,in studying the nitrogen nutrition of gramineous and leguminous crops1 they discovered that the gramineous plants died in absence of nitrate1 and in its presence made growth which increased regularly with nitrate supply2 while leguminous plants sometimes died and sometimes flourished in absence of nitrate1 and behaved equally erratically with increasing nitrate supply4 ,when the plants flourished nodules were invariably present on the roots1 but not otherwise4 ,they concluded1 therefore1 that the nitrogen nutrition of leguminous plants differed from that of the gramine1 and depended on some factor which sometimes came into their experiments and sometimes did not1 and1 in any case1 was associated with the nodule4 ,knowing that the nodules on the roots of leguminous plants contained bacteria-like bodies1 and remembering ,berthelot's results1 they explored the possibility of bacterial fixation4 ,they sterilised the sand and found that peas invariably failed to develop nodules and died1 but after adding a little garden soil nodules were found and vigorous growth was obtained4 ,c 8,of the leguminous plants the bean best reinvigorates the ground 444 because the plant is of loose growth and rots easily1 wherefore the people of ,macedonia and ,thessaly turn over the ground when it is in flower0 7i4e4 dig it into the ground if the soil is poor74 ,theophrastus1 8,enquiry into ,plants10 bk4 viii4 #b1 and bk4 ix4 ,i4 ,this book is of profound interest to agriculturists and botanists4 ,an excellent translation by ,sir ,arthur ,hort is now available4 7,loeb's ,classical ,library47 ,chemical analysis showed considerable fixation of gaseous nitrogen1 which ,hellriegel associated with the nodule organism4 ,this has proved to be correct1 and the fixation of nitrogen by bacteria is now a well-recognised process1 the conditions of which are being thoroughly worked out4 ,two types of organisms are known--those associated with leguminous plants1 and those living in a free and independent state in the soil4 ,of the latter the ,clostridium1 isolated by ,winogradsky1 is anaerobic1 and the ,azotobacter of ,beijerinck is aerobic4 ,the essential conditions are that a source of energy must be supplied--usually given as sugar--that the medium must not be acid1 and that sufficient phosphate must be present4 ,all this brilliant work had been accomplished in the short space of the ten years #ahhj to #ahij4 ,the inspiration had in each instance come from ,france1 and is traceable direct to ,pasteur1 although coming long after his own work on bacteriology4 ,it is impossible for us now to realise the thrill of wonder and astonishment with which students1 teachers1 and writers of those days learned that the nutrition of plants1 and therefore the growth of crops and the feeding of themselves1 was largely the result of the activity of bacteria in the dark recesses of the soil4 ,it is not surprising that the ideas were pushed somewhat too far1 that the soil population was regarded as solely bacterial1 and that important chemical and physical changes were sometimes overlooked4 ,gradually there came the inevitable reaction and a somewhat changed outlook4 ,continued examination showed the presence in soil of almost every kind of bacteria for which search was made4 ,some of them were almost certainly in the resting condition as spores1 and the new generation of workers had an uneasy feeling that the case for the overwhelming importance of bacteria in the economy of the soil was not too well founded4 ,it was shown that the decomposition of nitrogen compounds to form ammonia would take place without micro-organisms if1 as presumably would happen1 the plant enzymes continued to act after they got into the soil4 ,even the oxidation of ammonia to nitrate--the great stronghold of the biological school--was accomplished by chemical agents4 ,the fixation of nitrogen in soil conditions was beyond the power of chemists to achieve1 and here it was universally agreed that bacteria were the active agents4 ,and finally1 chemists were themselves bringing into prominence a set of bodies--the colloids--whose remarkable properties seemed indefinitely expansible1 and were in addition sufficiently incomprehensible to the ordinary student to attain much of the magnificence of the unknown4 ,all the time1 however1 a faithful body of workers was busy exploring the ground already won1 improving the technique1 making counts of the numbers of bacteria in the soil1 and trying to measure the amount of bacterial activity4 ,much of the value of this work was limited by the circumstance that the bacteria were regarded as more or less constant in numbers and activities1 so that a single determination was supposed to characterise the position in a given soil4 ,this was the condition of the subject when it was seriously taken up at ,rothamsted4 ,before turning to agriculture1 the writer had been studying the mechanism of certain slow chemical oxidations1 and one of his first experiments in agriculture was to examine the phenomena of oxidation in soil4 ,the results accorded with the biological explanation of ,schloesing3 when the soil was completely sterilised oxidation almost ceased4 ,but the striking discovery was made1 as the result of an accident to an autoclave1 that partial sterilisation increased the rate of oxidation1 and therefore presumably the bacterial activity4 ,this remarkable phenomenon had1 however1 already been observed1 and it had been shown that both bacterial numbers and soil fertility were increased thereby4 ,a full investigation was started in #aijg by ,dr4 ,hutchinson and the writer4#i ,from the outset the phenomena were recognised as dynamic and not static1 and the rates of change were always determined3 thus the bacterial numbers1 the nitrate and ammonia present were estimated after the several periods4 ,close study of the curves showed that the chemical and bacterial changes were sufficiently alike to justify the view that bacteria were in the main the causes of the production of ammonia and of nitrate2 although non-biological chemical action was not excluded1 there was no evidence that it played any great part4 ,thus the importance of micro-organisms in the soil was demonstrated4 ,the factor causing the increased bacterial numbers after partial sterilisation was studied by finding out what agents would1 and what would not1 allow the numbers to increase1 e4g4 it was found that the bacterial increases became possible when soil had been heated at #ef ,c41 but not at #dj ,c4 ,again1 it was shown that the high numbers in partially sterilised soils rose for a time even higher if a little fresh untreated soil were incorporated into the partially sterilised soil1 but afterwards they fell considerably4 ,putting all the results together1 it appeared that some biological cause was at work depressing the numbers of bacteria in normal soils1 but not--or not so much--in the partially sterilised soils4 ,studied in detail1 the data suggested protozoa as the agent keeping down bacterial numbers1 and they were found in the untreated1 but not in the treated1 soils4 ,the hypothesis was therefore put forward that bacteria are not the only members of the soil population1 but that protozoa are also present keeping them in check1 and therefore adversely affecting the production of plant food4 ,this conclusion aroused considerable controversy4 ,it was maintained that protozoa were not normal inhabitants of the soil1 but only occasional visitants1 and1 in any case1 they were only there as cysts2 the soil conditions1 it was urged1 were not suitable to large organisms like protozoa4 ,the objection was not to be treated lightly1 but1 on the other hand1 the experiments seemed quite sound4 ,as neither ,dr4 ,hutchinson nor the writer were protozoologists1 ,dr4 ,t4 ,goodey and 7after he left7 ,mr4 ,kenneth ,r4 ,lewin were invited to try and find out1 quite independently of the partial sterilisation investigation1 whether protozoa are normal inhabitants of the soil1 and if so1 whether they are in a trophic condition1 and what is their mode of life and their relation to soil bacteria4 ,had it turned out that protozoa had nothing to do with the matter1 search would have been made for some other organism4 ,goodey showed that the ciliates were not particularly important2 ,lewin soon demonstrated the existence of trophic amb and flagellates4 ,unfortunately he was killed in the war before he had got far with the work4 ,after the ,armistice1 ,mr4 ,cutler accepted charge of the work3 he will himself relate in ,chapters ,,iv4 and ,v4 what he has done4 ,at first sight it might be thought comparatively easy to settle a question of this kind by examining soil under a microscope or by sterilising it and introducing successively bacteria and known types of protozoa4 ,unfortunately neither method is simple in practice4 ,it is impossible to look into the soil with a microscope1 and methods of teasing-out small pieces of soil on a slide under the high1 or even the low power1 give no information1 because the particles of soil have the remarkable power of attracting and firmly retaining protozoa1 and no doubt bacteria as well2 indeed1 for protozoa 7which have been the more fully investigated7 there seems to be something not unlike a saturation capacity 7see ,fig4 #i1 p4 #gh74 ,further1 complete sterilisation of soil cannot be effected without at the same time altering its chemical and physical properties1 and changing it as a habitat for micro-organisms4 ,cutler has1 however1 overcome the difficulties and shown that the introduction of protozoa into soils sterilised and then reinfected with bacteria considerably reduces the numbers of these organisms4 ,the method adopted1 therefore1 is to take a census of population and of production4 ,counting methods are elaborated1 and estimates as accurate as possible are made of the numbers of the various organisms in a natural field soil at stated intervals4 ,simultaneously1 wherever possible some measure is taken of the work done4 ,the details of the census are finally arranged in consultation with the ,statistical ,department1 to ensure that the data shall possess adequate statistical value4 ,from the results it is possible to adduce information of great value as to the life of the population1 the influence of external conditions1 etc4 ,the most important investigation of this kind carried out at ,rothamsted was organised by ,mr4 ,cutler4#c ,a team of six workers was assembled1 and for #cfe days without a break they counted every day the ciliates1 the amb1 the flagellates1 and the bacteria in a plot of arable ground1 distinguishing no less than seventeen different kinds of protozoa4 ,the conclusions arrived at were carefully tested by the ,statistical ,department4 ,of the protozoa the flagellates were found to be the most numerous1 the amb came next1 and the ciliates were by far the fewest4 ,the numbers of each organism varied from day to day in a way that showed conclusively the essentially trophic nature of the protozoan population4 ,the numbers of amb--especially ,dimastigamba and of a species called --were sharply related to the numbers of bacteria3 when the ambae were numerous the bacteria were few1 and vice versa4 ,detailed examination showed that the amb were probably the cause of the fluctuations in the bacterial numbers1 but ,mr4 ,cutler has not yet been able to find why the amb fluctuated2 it does not appear that temperature1 moisture content1 air supply or food supply were determining causes4 ,the flagellates and ciliates also showed large fluctuations1 amounting in one case--,oicomonas--to a definite periodicity1 apparently1 however1 not related to bacterial numbers1 or1 so far as can be seen1 to external conditions of moisture1 temperature and food supply1 and showing no agreement with the fluctuations of the amb4 ,however1 one cannot be certain that lack of agreement between curves expressing protozoan numbers and physical factors implies absence of causal relationships3 the observations 7though the best that can yet be made7 are admittedly not complete4 ,if we saw only the end of the bough of a tree1 and could see no connection with a trunk1 we might have much difficulty in finding relationships between its motion and the wind2 whatever the direction of the wind it would move backwards and forwards in much the same way1 and even when the wind was blowing along the plane of its motion it would just as often move against the wind as with it4 ,meanwhile evidence was obtained that the twenty-four hour interval adopted by the protozoological staff was too long for bacteria1 and accordingly the ,bacteriological ,department1 under ,mr4 ,thornton1 refined the method still further4 ,bacterial counts were made every two hours1 day and night1 for several periods of sixty or eighty hours without a break4 ,the shape of the curve suggests that two hours is probably close enough1 and for the present counts at shorter intervals are not contemplated4 ,but there is at least one maximum and one minimum in the day1 although the bacterial day does not apparently correspond with ours1 nor can any relationship be traced with the diurnal temperature curve4 ,the nitrate content of the soil was simultaneously determined by ,mr4 ,page and found to vary from hour to hour1 but the variations did not sharply correspond with the bacterial numbers2 this1 however1 would not necessarily be expected4 ,the production of nitrate involves various stages1 and any lag would throw the nitrate and bacterial curves out of agreement4 ,there is a suggestion of a lag1 but more counts are necessary before it can be regarded as established4 ,examination of these and other nitrate curves obtained at ,rothamsted has brought out another remarkable phenomenon4 ,no crop is growing on these plots1 and no rain fell during the eighty hours1 yet nitrate is disappearing for a considerable part of the time4 ,where is it going to8 ,at present the simplest explanation seems to be that it is taken up by micro-organisms4 ,a similar conclusion had to be drawn from a study of the nitrogen exhaustion of the soil4 ,the whole of the nitrate theoretically obtainable from the organic matter of the soil is not obtained in the course of hours or even days2 in one of our experiments at ,rothamsted nitrification is still going on1 and is far from complete1 even after a lapse of fifty-three years4 ,the explanation at present offered is that part of the nitrate is constantly being absorbed by micro-organisms and regenerated later on4 ,now what organisms could be supposed to absorb nitrates from the soil8 ,certain bacteria and fungi are known to utilise nitrates1 and one naturally thinks of alg as possible agents also4 ,dr4 ,muriel ,bristol was therefore invited to study the alg of the soil4 ,her account is given in ,chapter ,,vi4 ,she has found them not only on the surface1 but scattered throughout the body of the soil1 even in the darkness of #d inches1 #e inches1 or #f inches depth1 where no light can ever penetrate1 and where photosynthesis as we understand it could not possibly take place4 ,some modification in their mode of life is clearly necessary1 and it may well happen that they are living saprophytically4 ,dr4 ,bristol has not yet1 however1 been able to count the alg in the soil with any certainty1 although she has made some estimates of the numbers4 ,the quantitative work on the soil population indicates other possibilities which are being investigated4 ,there is not only a daily fluctuation in the numbers1 but so far as measurements have gone1 a seasonal one also4 ,there seems to be some considerable uplift in numbers of bacteria1 protozoa1 and possibly alg and fungi in the spring-time1 followed by a fall in summer1 a rise in autumn1 and a fall again in winter4 ,at present we are unable to account for the phenomenon1 nor can we be sure that it is general until many more data are accumulated4 ,in the cases of the protozoa and the alg1 there was a definite reason for seeking them in the soil4 ,another section of the population1 the fungi1 was simply found1 and at present we have only limited views as to their function4 ,the older workers considered that they predominated in acid soils1 while bacteria predominated in neutral soils4 ,present-day workers have shown that fungi1 including actinomycetes1 are normal inhabitants of all soils4 ,the attempts at quantitative estimations are seriously complicated by the fact that during the manipulations a single piece of mycelium may break into fragments1 each of which would count as one1 while a single cluster of spores might be counted as thousands4 ,little progress has therefore been made on the quantitative lines which have been so fruitful with protozoa4 ,dr4 ,brierley gives1 in ,chapters ,,vii4 and ,,viii41 a critical account of the work done on fungi4 ,in addition to the organisms already considered there are others of larger size4 ,the nematodes are almost visible to the unaided eye1 most of them are free living and probably help in the disintegration of plant residues1 though a few are parasitic on living plants and do much injury to clover1 oats1 and less frequently to onions1 bulbs1 and potatoes4 ,further1 there are insects1 myriapods and others1 the effects of which in the soil are not fully known4 ,special importance attaches to the earthworms1 not only because they are the largest in size and in aggregate weight of the soil population1 but because of the great part they play in aerating the soil1 gradually turning it over and bringing about an intimate admixture with dead plant residues1 as first demonstrated by ,darwin4 ,earthworms are the great distributors of energy material to the microscopic population4 ,systematic quantitative work on these larger forms is only of recent date1 and ,dr4 ,imms1 in ,chapter ,,ix41 discusses our present knowledge4 ,,table ,i4 ,,soil ,,population1 ,,rothamsted1 #aibb4 7,the figures for alg and fungi are first approximations only1 and have considerably less value than those for bacteria and protozoa47 ---------------------------------------- ------------------------- ,approximate ,weight per ,acre of-- ------------------------------ ,numbers ,living ,dry ,matter ,nitrogen per ,gram ,organ- in ,organ- in ,organ- of ,soil4 isms4 isms4 isms4 ---------------------------------------- ----------------------- ,bacteria-- lb4 lb4 lb4 ,high level #de1jjj1jjj #ej #b #jb ,low level #bb1ejj1jjj #be ,protozoa-- ,ciliates-- ,high level #a1jjj -- -- -- ,low level #ajj -- -- -- ,amb-- ,high level #bhj1jjj #cbj #ab #ab ,low level #aej1jjj #agj ,flagellates-- ,high level #ggj1jjj #aij #g #jg ,low level #cej1jjj #he ,alg 7not blue-green7 #ajj1jjj #abe #f #jf ,blue-green ,not known4 ,say #f ,say #jf ,fungi-- ,high level #a1ejj1jjj #agjj #fj #fj ,low level #gjj1jjj #hjj --------------------- #ic #ic #d parts nitrogen per #a1jjj1jjj of soil4 ---------------------------------------- ------------------------ -------------------------------------- ,,larger ,,organisms4 ------------------------------------ ,numbers per ,acre4,d ------------------ ,unma- ,manured4 nured4 ----------------------------------- ,oligochaeta 7,limicolae7-- ,nematoda1 etc4 #c1fji1jjj #gid1jjj ,myriapoda #a1gha1jjj #hgi1jjj ,insects #g1gbg1jjjb1dge1jjj ,earthworms #a1jaj1jjj #deh1jjj ----------------------------------- -------------------------------------- ---------------------------------------- ------------------- ,,larger ,,organisms4 ---------------------------------------- ------------------ ,approximate ,weight per ,acre of-- --------------------------------------- ,living ,dry ,matter ,nitrogen in ,organisms4 in ,organisms4 ,organisms4 ------------------------------------ ,ma- ,unma- ,ma- ,unma- ,ma- ,unma- nured4nured4nured4nured4nured4nured4 ---------------------------------------- ------------- ,oligochaeta 7,limicolae7-- lb4 lb4 lb4 lb4 lb4 lb4 ,nematoda1 etc4 #i #b #c #a -- -- ,myriapoda #bjc #ii #he #db #d #b ,insects #cd #af #ad #f #a #a ,earthworms #dgb #bag #ajh #ej #aj #e ---------------------------------------- ------------- ,total #baj #ii #ae #i ---------------------------------------- --------------- ,total organic matter 7dry weight7 in this soil #abf1jjj lb4 per acre4 ,total nitrogen #egjj lb4 per acre4 7#a lb4 nitrogen per acre #jd parts per #a1jjj1jjj of soil47 ,d ,to a depth of #i inches4 ,the weight of soil is approximately #a1jjj1jjj kilos4 ,are there any other members of the soil population that are of importance8 ,as already shown1 the method of investigating the soil population in use at ,rothamsted is to find by chemical methods the changes going on in the soil2 to find by biological methods what organisms are capable of bringing about these changes2 and then to complete the chain of evidence by tracing the relationships between the numbers or activities of these organisms and the amount of change produced4 ,the list as we know it to-day is given in ,table ,i4 ,the method1 however1 does not indicate whether the account is fairly complete1 or whether there are other organisms to be found4 ,we might1 of course1 trust to empirical hunting for organisms1 or to chance discoveries such as led ,goodey to find the mysterious ,proteomyxan ,rhizopods1 which cannot yet be cultured with certainty1 so that they are rarely found by soil workers4 ,it is possible that there are many such organisms1 and it is even conceivable that these unknown forms far outnumber the known4 ,the defect of the present method is that it always leaves us in doubt as to the completeness of the list1 and so we may have to devise another4 ,reverting to ,table ,i41 it obviously serves no purpose to add the numbers of all the organisms together4 ,we can add up the weights of living organisms1 of their dry matter or nitrogen1 so as to form some idea of the proportion of living to non-living organic matter1 and this helps us to visualise the different groups and place them according to their respective masses4 ,but a much better basis for comparing the activities of the different groups would be afforded by the respective amounts of energy they transform1 if these could be determined4 ,it is proposed to attempt such measurements at ,rothamsted4 ,the results when added would give the sum of the energy changes effected by the soil population as we know it3 the figure could be compared with the total energy change in the soil itself as determined in a calorimeter4 ,if the two figures are of the same order of magnitude1 we shall know that our list is fairly well complete2 if they are widely different1 search must be made for the missing energy transformers4 ,there are1 of course1 serious experimental difficulties to be overcome1 but we believe the energy relationships will afford the best basis for further work on the soil population4 ,finally1 it is necessary to refer to the physical conditions obtaining in the soil4 ,these make it a much better habitat for organisms than one might expect4 ,at first sight one thinks of the soil as a purely mineral mass4 ,this view is entirely incorrect4 ,soil contains a considerable amount of plant residues1 rich in energy1 and of air and water4 ,the usual method of stating the composition of the soil is by weight1 but this is misleading to the biologist because the mineral matter has a density some two and a half times that of water and three times that of the organic matter4 ,for biological purposes composition by volume is much more useful1 and when stated in this way the figures are very different from those ordinarily given4 ,table ,,ii4 gives the results for two ,broadbalk arable plots1 one unmanured and the other dunged2 it includes also a pasture soil4 ,the first requirement of the soil population is a supply of energy1 without which it cannot live at all4 ,all our evidence shows that the magnitude of the population is limited by the quantity of energy available4 ,the percentage by weight of the organic matter is about two to four or five1 and the percentage by volume runs about four to twelve4 ,not all of this1 however1 is of equal value as source of energy4 ,about one-half is fairly easily soluble in alkalis1 and may or may not be of special value1 but about one-quarter is probably too stable to be of use to soil organisms4 ,a second requirement is water with which in this country the soil is usually tolerably well provided4 ,even in prolonged dry weather the soil is moist at a depth of #c inches below the surface4 ,it is not uncommon to find #aj per cent4 or #bj per cent4 by volume of water present1 spread in a thin film over all the particles1 and completely saturating the soil atmosphere4 ,,table ,,ii4 ,,volume ,,of ,,air1 ,,water ,,and ,,organic ,,matter ,,in #ajj ,,volumes ,,of ,,rothamsted ,,soil4 ---------------------------------------- ----- ,in ,pore ,space4 ,values ,common- ,solid ,matter4 ly ,obtained4 ---------------- ------------- ,mineral4,organic4,pore ,space4 ,water4 ,air4 ---------------------------------------- --- 7#a7 #fb #d #cd #bc #aa 7#b7 #ea #aa #ch #cj #h 7#c7 #da #ab #dg #dj #g ---------------------------------------- --- 7#a7 ,arable1 no manure applied to soil4 7#b7 ,arable1 dung applied to soil4 7#c7 ,pasture4 ,the air supply is usually adequate owing to the rapidity with which diffusion takes place4 ,except when the soil is water-logged1 the atmosphere differs but little from that of the one we breathe4 ,there is more ,,co1 but only a little less oxygen4#h ,the mean temperature is higher than one would expect1 being distinctly above that of the air1 while the fluctuations in temperature are less4#e ,the reaction in normal soils is neutral to faintly alkaline2 p,h values of nearly #h are not uncommon4 ,results from certain ,english soils are shown on p4 #ah4 ,the soil reaction is not easily altered4 ,a considerable amount of acid must accumulate before any marked increase in intensity of p,h value occurs2 in other words1 the soil is well buffered4 ,the same can be said of temperature1 of water1 and of energy supply4 ,like the reaction1 they alter but slowly1 so that organisms have considerable time in which to adapt themselves to the change4 ,,hydrogen ,,ion ,,concentration ,,and ,,soil ,,fertility4 p,h ,alkaline #aj ---- ,sterile3 ,alkali soil4 #i ---- #h ---- ,fertile3 ,arable4 ,neutral #g ---- #f ---- #e ---- ,potato ,scab fails4 ,nitrification hindered4 #d ---- ,barley fails4 ,acid #c ---- ,sterile3 ,peat4 ,a ,,selected ,,bibliography4 #a ,berthelot1 ,marcellin1 8,fixation directe de l'azote atmosphrique libre par certains terrains argileux10 ,compt4 ,rend41 #ahhe1 ci41 #gge-hd4 #b ,boussingault1 ,j4 ,b41 and ,lwy1 8,sur la composition de l'air confin dans la terre vgtale10 ,ann4 ,chim4 ,phys41 #ahec1 xxxvii41 #e-ej4 #c ,cutler1 ,d4 ,w41 ,crump1 ,l4 ,m41 and ,sandon1 ,h41 8,a ,quantitative ,investigation of the ,bacterial and ,protozoan ,population of the ,soil1 with an ,account of the ,protozoan ,fauna10 ,phil4 ,trans4 ,roy4 ,soc41 ,series ,b1 #aibb1 ccxi41 #cag-ej4 #d ,hellriegel1 ,h41 and ,wilfarth1 ,h41 8,untersuchungen ber die ,stickstoffnahrung der ,gramineen und ,leguminosen10 ,zeitsch4 des ,vereins f4 d4 ,rbenzucker-,industrie1 #ahhh4 #e ,keen1 ,b4 ,a41 and ,russell1 ,e4 ,j41 8,the ,factors determining ,soil ,temperature10 ,journ4 ,agric4 ,sci41 #aiba1 xi41 #baa-cg4 #f ,lawes1 ,j4 ,b41 and ,gilbert1 ,j4 ,h41 8,on ,agricultural ,chemistry1 ,especially in ,relation to the ,mineral ,theory of ,baron ,liebig10 ,journ4 ,roy4 ,agric4 ,soc41 #ahea1 xii41 #a-dj4 #g ,liebig1 ,justus1 8,chemistry in its ,application to ,agriculture and ,physiology10 #ast and #bnd editions 7#ahdj and #ahda71 #crd and #dth editions 7#ahdc and #ahdg72 8,natural ,laws of ,husbandry10 #ahfc4 #h ,russell1 ,e4 ,j41 and ,appleyard1 ,a41 8,the ,composition of the ,soil ,atmosphere10 ,journ4 ,agric4 ,sci41 #aiae1 vii41 #a-dh2 #aiag1 viii41 #che-dag4 #i ,russell1 ,e4 ,j41 and ,hutchinson1 ,h4 ,b41 8,the ,effect of ,partial ,sterilisation of ,soil on the ,production of ,plant ,food10 ,journ4 ,agric4 ,sci41 #aiji1 iii41 #aaa-ad2 ,part ,,ii41 ,journ4 ,agric4 ,sci41 #aiac1 v41 #aeb-bba4 #aj ,schloesing1 ,th41 and ,mntz1 ,a41 8,sur la ,nitrification par les ferments organiss10 ,compt4 ,rend41 #ahgg1 lxxxiv41 #cja-c2 #ahgg1 lxxxv41 #ajah-bj2 and #ahgh1 lxxxvi41 #hib-e4 8,leons de chimie agricole10 #ahhc4 #aa ,warington1 ,r41 8,on ,nitrification10 ,part ,i41 ,journ4 ,chem4 ,soc41 #ahgh1 xxxiii41 #dd-ea2 ,part ,,ii1 ,journ4 ,chem4 ,soc41 #ahgi1 xxxv41 #dbi-ef2 ,part ,,iii41 ,journ4 ,chem4 ,soc41 #ahhd1 xlv41 #fcg-gb2 ,part ,,iv41 ,journ4 ,chem4 ,soc41 #ahia1 lix41 #dhd-ebi4 #ab ,way1 ,j4 ,t41 8,on the ,composition of the ,waters of ,land ,drainage and of ,rain10 ,journ4 ,roy4 ,agric4 ,soc41 #ahef1 xvii41 #abc-fb4 #ac ,winogradsky1 ,s41 8,recherches sur les organismes de la nitrification10 ,ann4 de l',inst4 ,pasteur1 #ahij1 iv41 #a;e ,mmoire1 #bac-ca2 #b;e ,mmoire1 #beg-ge2 #c;e ,mmoire1 #gfj-ga4 8,recherches sur l'assimilation de l'azote libre de l'atmosphre par les microbes40 ,arch4 des ,sci4 ,biolog4 ,st4 ,petersburg1 #ahie1 iii1 #big-ceb4 ,for further details and fuller bibliography1 see ,e4 ,j4 ,russell1 8,soil ,conditions and ,plant ,growth10 ,longmans1 ,green ,co4 ,,chapter ,,ii4 ,,soil ,,bacteria4 ,a4 ,,occurrence ,,and ,,methods ,,of ,,study4 ,to understand the development of our knowledge of soil bacteria1 it must be remembered that bacteriology is under the disadvantage that it started as an applied science4 ,although bacteria were first seen by ,leeuwenhoeck about the middle of the seventeenth century1 and some of their forms described by microscopists of the eighteenth and early nineteenth centuries1 it was only with the work of ,pasteur on fermentation1 and of ,duvaine1 ,pasteur1 and their contemporaries on disease bacteria1 that bacteriology may be said to have started4 ,from the outset1 therefore1 attention has been directed mainly to the bacteria in their specialised relationship to disease or to fermentation and similar processes4 ,as a result1 little research was done on the pure biology of the bacteria1 so that even now many of the most fundamental and elementary problems concerning them are quite unsolved4 ,in their work on fermentations and disease bacteria1 the earlier workers were assisted by the fact that under both sets of conditions the causative bacteria exist1 as a rule1 either in practically pure culture1 or else in preponderating numbers4 ,the study and elucidation of such a mixed micro-population as exists in the soil1 became possible only when methods had been devised for isolating the different kinds of bacteria1 and thus studying them apart from each other4 ,it was the development of the gelatine plate method of isolating pure cultures by ,koch#cf in #ahha that made the study of the soil bacteria practicable4 ,the plating method opened up two lines of research4 ,in the first place1 it provided a simple means of isolating organisms from the mixed population of the soil1 and thus enabled a qualitative study to be made of each organism in pure culture1 and1 in the second place1 from it was developed a counting technique for estimating differences in bacterial numbers between samples of soil1 from which has sprung much of our knowledge of the quantitative side4 ,the earliest studies of the soil bacteria consisted of such estimations of numbers1 and showed that the soil contained a very numerous population of bacteria4 ,about #bj1jjj1jjj bacteria per gram of soil is now considered a fair average number4 ,the number and variety of bacteria existing in the soil is so enormous that the method of separating out all the different forms1 and of discovering their characters and functions1 has proved impracticable4 ,in practice1 therefore1 the problem has been approached from the biochemical standpoint4 ,that is to say1 the special chemical changes that the bacteria produce in the soil have first been investigated1 and this has been followed by the isolation and study of the various groups of bacteria that bring about the changes under investigation4 ,the method commonly employed in isolating the organisms that produce a given chemical change in the soil is called the 8elective0 method4 ,the soil is inoculated into a culture medium that will especially favour the group of bacteria to be isolated1 to the exclusion of others4 ,for example1 if it is desired to isolate the organisms that attack cellulose1 a medium is made up containing no other organic carbon compounds except cellulose4 ,such a selective medium encourages the growth of the group of organisms to be investigated1 so that after several transfers to fresh medium a culture is obtained containing only two or three different types of organisms4 ,these are separated by plating and pure cultures obtained4 ,another difficulty which has not yet been completely overcome is that of adequately describing an organism when it is isolated4 ,the morphology of bacteria is not the constant thing that is seen in the more stable higher organisms4 ,in many cases the appearance of a single strain is entirely different on different media1 and may be quite altered by such conditions as changes in acidity of the medium or temperature of incubation4 ,even on a single medium remarkable changes in morphology occur1 at any rate1 in some bacteria4 ,this is well seen in a cresol-decomposing organism under investigation at ,rothamsted4 ,in cultures a few days old this organism develops as bent and branching rods2 these rods then break up into chains of cocci and short rods1 which separate1 and in old cultures all the organisms may be in the coccoid form 7,fig4 #a74 ,it is claimed by ,lhnis#dg;b that the possession of a complex life-cycle of changing forms is a universal character in the bacteria4 ,the instability of shape in many bacteria makes it necessary to standardise very carefully the cultural conditions under which they are kept when their appearance is described4 ,illustration3 ,culture #ae hours old4 ,culture #c days old4 ,,fig4 #a4--;,change in appearance1 in culture1 of a cresol decomposing bacterium4 ,the inadequacy of mere morphology as a basis for describing bacteria led to the search for diagnostic characters1 based on the biochemical changes that they produced in their culture media1 and the appearance of their growth in the mass on various media4 ,these characters unfortunately have also proved to be very much influenced by the exact composition of the medium and other conditions of culture4 ,recently an attempt has been made by the ,american ,society of ,bacteriologists to standardise the diagnostic characters used in describing bacteria1 and also the media and cultural conditions under which they are grown for the purpose of description4 ,the need for such precautions1 however1 was not sufficiently realised by the early workers1 many of whose descriptions cannot now be referred to any definite organism4 ,the large number of organisms found in the soil1 and the difficulty and labour of adequately describing them1 is such that even now we have no comprehensive description of the common soil bacteria that appear on gelatine platings4 ,a careful study based on modern methods of characterisation has been made of certain selected groups of bacteria1 and it is hoped that the laborious systematic work of describing the common forms will gradually be completed4 ,several attempts have been made to classify the bacteria that appear commonly on gelatine platings4 ,this work was commenced by ,hiltner and ,stormer in ,germany1 and continued by ,chester1 ,harding1 and ,conn in ,america4 ,conn#aj1ad found that the common organisms fell into the following main groups3-- 7#a7 ,large spore-forming bacteria1 related to ,bacillus subtilis1 which form about #e-aj per cent4 of the numbers4 ,he adduced evidence#ab1ac that these organisms exist in the soil mainly as spores1 so that they may not form an important part of the active soil population4 7#b7 ,short non-sporing organisms1 related to ,pseudomonas fluorescens1 that are rapid gelatine liquefiers4 ,these form another #aj per cent4 of the numbers4 7#c7 ,short rod forms that liquefy gelatine slowly or not at all1 and develop colonies very slowly4 ,these form #dj-ge per cent4 of the numbers1 and may therefore be of considerable importance in the soil4 7#d7 ,a few micrococci also occur4 ,these groups comprise the larger portion of the bacterial flora of the soil1 but1 in addition to these organisms1 that develop on the media commonly used for plating1 there are special and important groups that appear only on special media1 either owing to their being unable to grow on ordinary media or because they get swamped by other forms4 ,examples of such groups are the ammonia and nitrite oxidising bacteria1 the nitrogen fixing groups1 the cellulose decomposing organisms1 and the sulphur bacteria4 ,in order that we may apply the results of the study of a definite organism to other localities1 a knowledge of the geographical distribution of the soil bacteria is clearly needed4 ,we have1 unfortunately1 very little knowledge of the distribution of soil organisms4 ,the common spore-forming groups appear to be universally distributed4 ,thus ,barthel1 in a study of the bacterial flora of soils from ,greenland and the island of ,disko1 obtained soil organisms belonging to the groups of ,bacillus subtilis1 ,b4 amylobacter1 ,b4 fluorescens1 ,b4 caudatus1 and ,b4 ,zopfii1 which are common groups in ,european soil1 indicating that the general constitution of the bacterial flora of the soil in arctic regions is not widely different from that of ,western ,europe4 ,bredemann1 who made an extensive study of the ,bacillus amylobacter group1 obtained soil samples from widely scattered localities1 and found these organisms in soil from ,germany1 ,holstein1 ,norway1 ,italy1 ,morocco1 ,teneriffe1 ,russia1 ,japan1 ,china1 the ,east ,indies1 ,samoa1 ,illinois1 ,arizona1 ,german ,east ,africa1 and the ,cameroons4 ,some soil organisms1 on the other hand1 are apparently absent from certain districts4 ,this may be due to the conditions1 such as climatic environment1 being unfavourable to them4 ,a study has recently been made at ,rothamsted of the distribution over ,great ,britain of a group of bacteria that are capable of decomposing phenol and cresol4 ,one of these organisms1 apparently related to the acid-fast ,b4 phli1 has an interesting distribution4 ,it has been found in #ej per cent4 of the soils samples examined from the drier region1 where the annual rainfall is less than #cj inches1 but in only #bj per cent4 of the samples in the wetter parts of ,britain4 ,another example of limited distribution is found in the case of ,bacillus radicicola1 the organism that produces tubercles on the roots of leguminous plants4 ,the distribution of the varieties of this organism follows that of the host plants with which they are associated1 so that when a new leguminous crop is introduced into a country1 nodules may not appear on the roots unless the soil be specially inoculated with the right variety of organism4 ,in cases where a group of soil organisms is widely distributed over the globe1 it may yet be absent from many soils owing to the soil conditions not suiting it4 ,thus1 phenol decomposing bacteria1 though abundant in the neighbourhood of ,rothamsted1 are yet absent from field plots that have been unmanured for a considerable period4 ,the occurrence of the nitrifying organisms and the nitrogen fixing ,azotobacter is also very dependent on the soil conditions4 ,owing to the method by which our knowledge of soil bacteria has been acquired1 by studying first the chemical changes in the soil and then the bacteria that produce them1 it is natural for us to divide them into physiological groups according to the chemical changes that they bring about4 ,this grouping is the more reasonable since so little is known as to the true relationships of the different groups of bacteria that a classification based on morphology is well-nigh impossible4 ,in considering the activities of bacteria in the soil1 it is convenient to group the changes which they bring about into the two divisions into which they naturally fall in the economy of the organisms4 ,in the first place1 there are the changes that result in a release of energy1 which the bacteria utilise for their vital processes4 ,in the second place1 there are the processes by which the bacteria build up the material of their bodies4 ,these building up processes involve an intake of energy for their accomplishment4 ,it will be convenient to deal first with the release of energy for their own use by bacteria1 and its consequences4 ,b4 ,,activities ,,connected ,,with ,,the ,,acquirement ,,of ,,energy4 ,unlike the green plants1 most bacteria are unable to obtain the energy that is required for their metabolism from sunlight4 ,they must1 therefore1 make use of such chemical changes as will involve the release of energy4 ,as an example of the acquirement of energy in this way may be taken the oxidation of methane by ,b4 methanicus4 ,this organism1 described by ,shngen1 obtains its energy supply by the conversion of methane into ,,co and ,h,o4 ,,ch #b,o ,,co #b;,h,o #bbj ,cal4 ,a further example is the acetic organism that obtains its energy through the oxidation of alcohol to acetic acid4 ,c,h,o ,o ,c,h,o ,h,o #aae ,cal4 ,the decomposition processes brought about by micro-organisms in obtaining energy are usually oxidations1 but this is not necessarily so1 as can be seen in case of the fermentation of sugar into alcohol4,e ,c,h,o #b;,c,h,o #b;,,co #ej ,cal4 ,e ,these examples are from ,orla-,jensen 7,centralblatt f4 ,bakt41 ,,ii41 ,bd4 #bb1 p4 #cje74 ,by far the greater part of the decomposition of organic matter is brought about by bacteria in the process of acquiring energy4 ,in the soil1 nearly the whole of the material utilised by bacteria as a source of energy is derived ultimately from green plants4 ,the energy materials left in the soil by the plant fall into two groups1 the non-nitrogenous compounds1 which are mainly carbohydrates and their derivatives1 and the nitrogenous compounds1 principally derived from proteins4 7#a7 ,decomposition of ,non-nitrogenous ,compounds4 ,the simpler carbohydrates and starches are attacked and decomposed by a large variety of bacteria4 ,the addition of such substances to soil causes a rapid increase in bacterial numbers4 ,in nature the sugars are in all probability among the first plant constituents to be destroyed during the decay processes4 ,a large proportion of plant tissues consist of cellulose and its derivatives4 ,these compounds are consequently of great importance in the soil4 ,unfortunately our knowledge of the processes by which cellulose is broken down in the soil is very inadequate4 ,the early experimental study of cellulose decomposition1 such as that of ,tappeiner#fj and ,hoppe-,seyler1#cc was mostly carried out under conditions of inadequate aeration1 and the products of decomposition were found to include methane and ,,co1 and sometimes fatty acids and hydrogen4 ,the bacteriology of this anaerobic decomposition was studied by ,omelianski1#ed who described two spore-bearing organisms1 one of which attacked cellulose with the production of hydrogen1 and the other with the production of methane4 ,both species also produce fatty acids and ,,co4 ,it is probable that these organisms operate in the soil under conditions of inadequate aeration4 ,in swamp soils1 in which rice is grown1 it has been shown that methane1 hydrogen1 and ,,co are evolved in the lower layers4 ,in these soils1 however1 the methane and hydrogen are oxidised when they reach the surface layers4 ,this oxidation is also effected by micro-organisms4 ,bacteria capable of deriving energy by the oxidation of hydrogen gas have been isolated and studied by ,kaserer1#cg and by ,nabokich and ,lebedeff1#eb while ,shngen#eg has isolated an organism which he named ,bacillus methanicus1 that was capable of oxidising methane4 ,under normal conditions in cultivated soils1 however1 the decomposition of cellulose takes place in the presence of an adequate air supply1 and so follows a different course from that studied by ,omelianski4 ,our knowledge of this aerobic decomposition is very scanty4 ,a number of bacteria1 capable of decomposing cellulose aerobically1 are known4 ,a remarkable organism was investigated by ,hutchinson and ,clayton1#cj who named it ,spirochta cytophaga4 ,this organism1 which they isolated from ,rothamsted soil1 though placed among the ,spirochtoidea1 is of doubtful affinities4 ,during the active condition it exists for the most part as thin flexible rods tapered at the extremities4 ,this form passes into a spherical cyst-like stage1 at first thought to be a distinct organism 7,fig4 #b74 ,spirochta cytophaga is very aerobic1 working actively1 only at the surface of the culture medium4 ,it is very selective in its action4 ,it appears unable to derive energy from any carbohydrate other than cellulose4 ,indeed1 many of the simple carbohydrates1 especially the reducing sugars1 are toxic to the organism in pure culture4 ,an extensive study of aerobic cellulose decomposition by bacteria was made by ,mc,beth and ,scales1#ej who isolated fifteen bacteria having this power4 ,five of these were spore-forming organisms4 ,unlike ,spirochta cytophaga1 they are all able to develop on ordinary media such as beef agar or gelatine1 and are thus not nearly so selective in their food requirements4 ,illustration3 ,,fig4 #b4--,spirochta cytophaga4 ,changes occurring in culture4 7,after ,,hutchinson and ,,clayton47 ,we are at present ignorant as to which organisms are most effective in decomposing cellulose in the soil under field conditions1 or what are the conditions best suited to their activity4 ,it is possible that fungi also help in the decomposition of cellulose to a great extent4 ,this subject of the decomposition of cellulose offers one of the most promising fields of research in soil bacteriology4 ,the difficulty of the subject is further increased by our present ignorance of the chemical aspect of cellulose decomposition4 ,it has been supposed that the early decomposition products are simpler sugars1 but these are not found under conditions in which cellulose is being decomposed by pure cultures of the bacteria mentioned above4 ,hutchinson and ,clayton found that their organism produced volatile acids1 mucilage1 and a carotin-like pigment4 ,the organisms isolated by ,mc,beth and ,scales also produce acids1 and in some cases yellow pigments4 ,it is known1 however1 that the decomposition products of cellulose can be utilised as energy supply for other organisms1 such as nitrogen fixing bacteria4 ,when plant remains decompose in the soil there are ultimately produced brown colloidal bodies collectively known as humus4 ,the processes by which this humus is produced are not yet properly understood4 ,humus is of great importance in the soil1 in rendering the soil suitable for the growth of crops4 ,it affects the physical properties of the soil to a great extent4 ,in the first place1 it improves the texture of the soil1 making heavy clay soils more friable1 and loose sandy soils more coherent4 ,secondly1 it has great water-retaining powers1 so that soils rich in organic matter suffer comparatively little during periods of drought4 ,and lastly1 it exerts a strong buffering effect against soil acids4 ,now1 it is one of the problems of present-day farming that soil is becoming depleted of its humus4 ,this is due to the increasing scarcity of farmyard manure in many districts1 and the consequent use of mineral fertilisers to supply nitrogen1 potash1 and phosphate to the crop4 ,a need has therefore arisen for a substitute for farmyard manure1 by means of which the humus content of soils may be kept up in districts where natural manure is scarce4 ,illustration3 ,,fig4 #c4--;,cellulose decomposed by ,s4 cytophaga in media with increasing amounts of nitrogen4 7,after ,,hutchinson and ,,clayton47 ,x-axis3 ,milligrams of nitrogen supplied as sodium-ammonium phosphate4 ,y-axis3 ,milligrams of cellulose decomposed in #ba days4 ,it is well known that if fresh unrotted manure or straw be added to the soil1 it often produces harmful effects on the succeeding crop4 ,the problem1 therefore1 was to develop a method by which fresh straw1 before application to the soil1 could be made to rot down to a mixture of humus compounds such as occur in well-rotted farmyard manure4 ,the solution of this problem came as a result of an investigation by ,hutchinson and ,richards1#cj;b at ,rothamsted1 into food requirements of the cellulose decomposing bacteria4 ,they realised that since more than #aj per cent4 of the dry weight of bacteria consists of nitrogen1 it would be necessary to supply the cellulose decomposing bacteria with a supply of nitrogen1 in order that they should attain their greatest activity4 ,experiments with cultures of ,spirochta cytophaga showed that the amount of cellulose decomposed depended upon an adequate supply of nitrogen for the organism 7,fig4 #c74 ,similarly1 materials such as straw will scarcely decompose at all if wetted with pure water4 ,an adequate supply of nitrogen compounds is needed to enable decomposition to take place4 ,hutchinson and ,richards tested the effect of ammonium sulphate1 and discovered experimentally the proportion of ammonia to straw that produced the most rapid decomposition4 ,they found that if a straw heap was treated with the correct proportion of ammonia1 it decomposed into a brown substance having the appearance of well-rotted manure4 ,this has resulted in the development of a commercial process for making synthetic farmyard manure from straw4 ,the method of manufacture is as follows3 ,a straw stack is made and thoroughly wetted with water4 ,the correct amount of ammonium sulphate is then sprinkled on the top and wetted1 so that the solution percolates through the straw4 ,the cellulose bacteria attack the straw1 breaking it down and assimilating the ammonia4 ,this ammonia is not wasted1 as it is converted into bacterial protoplasm that eventually decays in the soil4 ,field trials of this synthetic manure show that it produces an effect closely similar to that of natural farmyard manure4 ,while cellulose and related carbohydrates are by far the most important non-nitrogenous compounds left in the soil by plants1 there are other compounds whose destruction by bacteria is of special interest4 ,such1 for example1 is the case of phenol4 ,this compound is produced by bacterial action as a decomposition product of certain amino-acids4 ,it occurs in appreciable amounts in cow urine4 ,it is probable that it forms a common decomposition product in soil and also in farmyard manure4 ,if this phenol were to persist in the soil1 it would eventually reach a concentration harmful to plant growth4 ,it does not1 however1 accumulate in the soil2 indeed1 if pure phenol or cresol be added to ordinary arable soil1 a rapid disappearance occurs4 ,this disappearance is of some practical importance1 since it limits the commercial use of these compounds as soil sterilising agents4 ,the cause of the disappearance has been to some extent elucidated at ,rothamsted1#eh where it was found to be in part a purely chemical reaction with certain soil constituents1 and partly due to the activity of bacteria capable of decomposing it4 ,a large number of soil bacteria have now been isolated that can decompose phenol1 meta-1 para-1 and ortho-cresol1 and are able to use these substances as the sole sources of energy for their life processes4 ,these organisms have a wide distribution1 having been found in soil samples taken from all over ,great ,britain1 from ,norway1 the ,tyrol1 ,gough ,island1 ,tristan da ,cunha and ,south ,georgia4 ,soil bacteria have also been isolated that are able to decompose and derive their energy from naphthalene and from toluene4 ,the ability of the bacteria to break up the naphthalene is very remarkable1 and all the more so since they can hardly have come across this compound in the state of nature4 ,the naphthalene organisms have a distribution as world-wide as the phenol group4 7#b7 ,ammonia ,production4 ,the second main group of products left in the soil by higher plants are the nitrogen-containing compounds1 such as the proteins and amino-acids4 ,plant remains are not the only source of organic nitrogen compounds available to soil bacteria4 ,there are1 in addition1 the dead bodies of other soil organisms1 such as protozoa and alg4 ,the relative importance of these sources of nitrogen is not known1 but almost certainly varies greatly with the state of activity of the various groups of the soil population4 ,bacteria are able to utilise organic nitrogen compounds as energy sources1 as can be exemplified in the oxidation of a simple amino-acid3-- ,h ,o _/_/ ,h--,c--,c #c,o #b;,,co ,h,o ,,nh #aeb ,cal4 ,,nh ,,oh ,it will be seen that1 in the acquirement of energy from such a compound1 ammonia is released as a by-product4 ,it is not certainly known what is the exact course of the reactions brought about by bacteria in soil during the breaking-down of organic nitrogen compounds1 but they result in the splitting off of most of the nitrogen as ammonia4 ,herein lies the great importance of the process1 for the production of ammonia is an essential stage in the formation of nitrate in the soil1 and on the supply of nitrate the growth of most crops largely depends4 ,illustration3 ,,fig4 #d4--,quantities of ammonia produced by pure cultures from #e grams of casein in the presence of varying quantities of dextrose4 7,after ,,doryland47 ,x-axis3 ,percentage of dextrose added4 ,y-axis3 ,milligrams of ,,nh produced4 ,it is very important to note that the production of this ammonia is only a by-product in the economy of the bacteria1 the benefit that they derive from the reactions being due to the release of energy involved in the decomposition4 ,the common ammonia-producing bacteria in the soil have been found equally capable of deriving their energy by the oxidation of sugars and similar non-nitrogenous compounds4 ,fig4 #d shows an experiment by ,doryland1#ag in which cultures of common soil bacteria were grown in peptone solution1 to which increasing quantities of sugar were added4 ,one can see that1 as the amount of sugar is increased1 the production of ammonia is lowered1 since the bacteria are obtaining energy from the sugar instead of from the nitrogen compound1 peptone4 ,consequently1 if soil contains a quantity of easily decomposible carbohydrate material1 bacteria will derive their energy from this source1 and the production of ammonia and nitrate will be lowered4 ,thus the addition of sugar or unrotted straw to the soil often lowers the nitrate production1 and consequently reduces the crop yield4 ,if the soil is sufficiently rich in carbohydrate material1 the bacteria may multiply until the supply of organic nitrogen is used up1 and then will actually assimilate some of the ammonia and nitrate already existing4 ,there is thus a balance of conditions in the soil due to varying proportions of nitrogenous and non-nitrogenous energy material4 ,when nitrogen compounds are the predominant energy source1 the bacteria utilise them1 and ammonia is released4 ,when a non-nitrogenous energy source predominates1 this is utilised and little or no ammonia is released1 and in extreme cases ammonia may be assimilated4 ,although a large number of the common organisms in the soil produce ammonia in culture media containing peptone1 the relative importance of these in the soil has yet to be decided4 ,it was supposed that the spore-forming organisms related to ,bacillus mycoides were of chief importance4 ,this supposition dates from the work of ,marchal1#di who studied the production of ammonia by an organism of this group in culture solution1 and found it to be a very active ammonifier4 ,as already mentioned1 however1 there is some doubt as to whether the large spore-forming organisms are very active under soil conditions4#ab1ac ,the existence of rapid fluctuations in nitrate content1 found to exist in soil1 may in the future indicate which are the most active of the common bacteria in the soil itself by enabling us to observe which types increase during periods of rapid ammonia and nitrate formation4 7#c7 ,nitrate ,production4 ,the ammonia produced in the soil under normal field conditions is rapidly oxidised successively to nitrite and to nitrate1 a process known as nitrification4 ,the process of nitrification is more rapid than that of ammonia production1 with the consequence that no more than traces of ammonia are able to accumulate4 ,the rate at which nitrate is formed in the soil is consequently set by the slower process of ammonia production4 ,the work of ,schloesing and of ,warington showed that the oxidation of ammonia was the work of living organisms4 ,it is1 however1 to ,winogradsky's isolation and study of the causative organisms that we owe our present knowledge of the biology of the process4 ,by a new and ingenious technique1 he isolated from soil two remarkable groups of bacteria that bring about nitrification4 ,the first group oxidises ammonium carbonate to nitrite1 and was divided by ,winogradsky into the two genera1 ,nitrosomonas1 a very short rod-like organism bearing a single flagellum1 and ,nitrosococcus1 a non-motile form found in ,south ,america4 ,the second group oxidises nitrites to nitrates4 ,they are minute pear-shaped rods to which he gave the name ,nitrobacter4 ,winogradsky found that the first1 or nitrite-producing group1 would live in a culture solution containing3-- #bbe grams ammonium sulphate1 #bj sodium chloride1 #aj magnesium carbonate1 to the litre of well water4 ,nitrobacter would grow in a similar medium containing sodium nitrite instead of ammonium sulphate4 ,there being no organic carbon in these media1 the organisms had no source of carbon for their nutrition1 except the ,,co of the air1 or possibly that of bicarbonate in solution4 ,it therefore followed that the organisms must obtain their carbon supply from one of these sources4 ,unlike green plants1 the nitrous and nitric organisms are able to carry on this carbon assimilation in the dark1 and must therefore obtain the energy needed for the process from some chemical reaction4 ,the only sources of energy in ,winogradsky's solutions were the nitrogen compounds1 and it consequently followed that the organisms must derive their energy supply by the oxidation of ammonia and nitrite respectively4 ,the release of energy obtained by these two reactions has been calculated by ,orla-,jensen to be as follows3-- 7,,nh7,,co #c,o #b;,,hno ,,co #c;,h,o #adh ,cals4 ,,kno ,o ,,kno #bb ,cals4 ,the exact process by which ammonium carbonate is converted into nitrite is not at present known4 ,the two groups of organisms are extremely selective in their source of energy4 ,the nitrous organisms can derive their energy only by the oxidation of ammonia to nitrite1 and the nitric organisms only by the oxidation of nitrite to nitrate4 ,in culture media they are1 indeed1 inhibited by soluble organic compounds such as sugars4 ,under natural conditions1 however1 they appear to be less sensitive1 since ammonium carbonate is readily nitrified in substrata rich in organic matter4 ,the rapid nitrification that takes place during the purification of sewage is an example of this4 ,the conditions in culture1 with regard to aeration and the removal of metabolic products from the neighbourhood of the organisms1 are very different from those in the soil1 and perhaps account for the discrepancies found4 ,the oxidation of ammonium carbonate by nitrosomonas results in the formation of nitrous acid4 ,the organisms are very sensitive to acidity1 and can only operate if the nitrous acid produced is neutralised by an available base4 ,in normal soils calcium carbonate supplies this base1 and in acid soils the formation of nitrite is1 as a rule1 increased by the addition of lime1 or of calcium or magnesium carbonate4 ,there is evidence that in the absence of calcium carbonate1 other compounds can be used as a base4 ,it was found by ,hopkins and ,whiting#cb that in culture solution the nitrifying organisms could use insoluble rock phosphate as a base1 producing therefrom the soluble acid phosphate4 ,there is evidence1 however1 that in ordinary soil containing calcium carbonate very little solution of phosphate takes place in this way4 ,the further oxidation of nitrite to nitrate by ,nitrobacter does not produce acid1 and requires no further neutralising base4 ,the nitrate produced in this way is the main source of nitrogen supply to plants under normal conditions4 ,experiments have shown that a number of plants are capable of utilising ammonia as a source of nitrogen1 and ,hesselmann#cd has found forest soils in ,sweden where no nitrification was proceeding1 and where1 therefore1 plants would presumably obtain their nitrogen in this way1 but such cases must be regarded as exceptional4 ,another group of bacteria capable of deriving their energy from an inorganic source exists in the soil4 ,this comprises the sulphur bacteria1 which are able to derive energy by the oxidation of sulphur1 sulphides1 or thiosulphates to sulphuric acid3-- ,s #c,o ,h,o ,h,,so #ada ,cals4 ,one organism studied by ,waksman and ,joffe#fc is able to live in inorganic solution1 deriving its carbon from carbon dioxide4 ,the sulphur bacteria have recently come into prominence in ,america owing to their faculty for producing acid4 ,thus ,thiospirillum will increase the acidity of its medium to a reaction of ,p,h #aj before growth ceases4 ,the potato scab disease in ,america is now treated by composting with sulphur4 ,this treatment depends on the production of sulphuric acid by the sulphur oxidising bacteria1 which renders the soil too acid for the parasite4 ,there is some evidence also that acid thus produced can be used to render insoluble phosphatic manures more available in the soil4 ,analogous to the sulphur organisms are certain bacteria isolated from sheep dig tanks in ,south ,africa by ,green1#bh;b which can derive energy by the oxidation of sodium arsenite to arsenate4 7#d7 ,anaerobic ,respiration4 ,as is seen in the examples mentioned1 energy is commonly obtained by bacteria through an oxidation process in which free oxygen is utilised4 ,in water-logged soil1 however1 or in soil overloaded with organic matter1 anaerobic bacteria may develop1 which obtain their oxygen from oxidised compounds4 ,thus there are soil organisms described by ,beijerinck#b and others which can obtain oxygen by reducing sulphates to sulphides4 ,a more important source of oxygen under these conditions is nitrate1 which can supply oxygen to a larger number of bacteria4 ,the stage to which the reduction can be carried varies according to the organism4 ,a very large number of bacteria are capable of reducing nitrates to nitrites4 ,many can reduce nitrate to ammonia1 and some can produce an evolution of nitrogen gas from nitrate4 ,the effects of nitrate reduction1 therefore1 appear under water-logged conditions in soils4 ,for example1 in swamp soils in which rice is grown1 it has been found by ,nagaoka1#ec in ,japan1 that treatment with nitrate of soda depresses the yield1 probably owing to the formation of poisonous nitrites by reduction4 ,under normal conditions of well aerated soil1 however1 it is unlikely that the reduction of nitrate is of great importance4 ,in such soils the activities through which bacteria acquire their energy are1 as we have seen1 of vital importance to the plant1 resulting in the disintegration of plant tissues1 with the ultimate formation of humus1 and in the production of nitrate4 ,in their activities connected with the building up of their protoplasm1 bacteria may1 on the other hand1 compete with the plant4 ,these activities and their consequences will be reviewed in the following chapter4 ,,chapter ,,iii4 ,,soil ,,bacteria4 ,c4 ,,activities ,,connected ,,with ,,the ,,building-,,up ,,of ,,bacterial ,,protoplasm4 7#a7 ,composition of ,bacteria4 ,the activities of the soil bacteria that we have yet to consider are those connected with the building-up from simpler materials of the protoplasm of the bacterial cell4 ,it is important to bear in mind that this process is one requiring an expenditure of energy on the part of the organism4 ,the sources of energy we have already considered4 ,the bodies of bacteria contain the same elements common to other living matter4 ,analyses of various bacteria have been made by a number of workers4 ,about #he per cent4 of their weight is made up of water4 ,this analysis of ,pfeiffer's ,bacillus by ,cramer#ae shows the typical percentages of carbon1 nitrogen1 hydrogen1 and ash in the dry matter3-- ,composition of ,pfeiffer's ,bacillus 7,cramer74 ,c #ej per cent4 ,n #abc ,h #ff ,ash #ia ,about #fe-gj per cent4 of the dry matter of bacteria consists of protein4 7#b7 ,sources of ,carbon4 ,the biggest constituent of the dry matter of bacteria is therefore carbon4 ,in the soil1 bacteria find an abundance of organic matter from which they may derive their carbon supply4 ,a special case1 however1 is furnished by the nitrifying organisms1 certain sulphur oxidising bacteria1 and others that derive their carbon from the ,,co of the soil atmosphere4 ,the sources from which these special groups obtain the necessary energy to accomplish this1 we have already considered4 7#c7 ,assimilation of ,nitrogen ,compounds4 ,of chief importance in its consequences are the means adopted by bacteria to obtain their nitrogen supply4 ,there is some reason to believe that soil bacteria do not take up protein and peptones as such1 but must first break down these bodies into simpler compounds4 ,when a sufficient amount of easily decomposable organic nitrogen is present in the soil1 the ammonifying bacteria use such compounds as sources of energy1 and in this case have a nitrogen supply exceeding their requirements4 ,but where there is an excess of carbohydrate or other non-nitrogenous source of energy available in the soil1 the case is different4 ,here the organisms have a supply of energy which enables them to multiply rapidly until the organic nitrogen is insufficient for their needs4 ,hence they turn to the ammonia and nitrate present in the soil1 and build up their proteins from this source4 ,doryland#ag has shown that many common soil ammonifiers assimilate ammonia and nitrate when supplied with carbohydrate4 ,there may thus be a temporary loss of nitrate from soil when sugar1 starch1 straw1 or such materials are added to it4 7#d7 ,fixation of ,free ,nitrogen4 ,the bacteria that we have so far considered take up their nitrogen directly from compounds containing this element4 ,there remain1 however1 a comparatively small but very important group of bacteria possessing the power of causing elemental nitrogen to combine1 and of building it up into their proteins4 ,this fixation of nitrogen by micro-organisms is a vital step in the economy of nature4 ,losses of nitrogen from the land are continually occurring through the washing-out of nitrates by rain1 and through the evolution of gaseous nitrogen during the processes of decay4 ,to maintain the supply of combined nitrogen which is essential to living organisms1 there must therefore be a compensating process by which the supply of nitrogen compounds in the soil is kept up4 ,it was discovered in the middle of the nineteenth century that if soil were kept moist and exposed to the air1 there was an increase in the amount of nitrogen compounds present4 ,berthelot1 in #ahic1 studied the nitrogen relationships of soil1 and recognised that this fixation of nitrogen in soil was the work of micro-organisms4 ,winogradsky followed up his work and isolated from soil a large anaerobic spore-forming organism1 capable of fixing nitrogen1 to which he gave the name ,clostridium pasteurianum4 ,in #aija the investigations of ,beyerinck1 in ,holland1 led to the important discovery of a group of large aerobic organisms1 which he named ,azotobacter4 ,these were found to be very active in fixing free nitrogen4 ,more recently1 a number of other nitrogen-fixing bacteria have been described1 and the property has been found to exist to a small extent in several previously well-known organisms4 ,it becomes important to determine which are the groups of bacteria whose nitrogen-fixing powers are of chief importance in the soil4 ,on account of its energetic fixation of nitrogen in culture media1 ,azotobacter has attracted the greatest attention of workers4 ,the evidence seems to be consistent with the view that ,azotobacter is of importance in the soil4 ,thus the distribution of ,azotobacter would appear to be world-wide4 ,it is found all over ,western ,europe and the ,united ,states4 ,lipman and ,burgess#de found it in soils collected from ,italy and ,spain1 ,smyrna1 ,cairo1 the ,fayum1 the ,deccan in ,india1 ,tahiti1 ,hawaii1 ,mexico1 ,guatemala1 and ,canada4 ,c4 ,m4 ,hutchinson#bi found it to be distributed throughout ,india4 ,it was found by ,omelianski#ee to be widely distributed in ,european and ,asiatic ,russia1 and by ,groenewege#bh in ,java4 ,ashby#a at ,rothamsted1 isolated it from soils from the ,transvaal1 ,east ,africa1 and ,egypt4 ,also1 an association has sometimes been found between the ability of a soil to fix nitrogen and the occurrence and vigour of its ,azotobacter flora4 ,thus ,lipman and ,waynick#df found that if soil from ,kansas were removed to ,california1 its power to produce a growth of ,azotobacter1 when inoculated into a suitable medium1 was lost1 and1 at the same time1 its nitrogen-fixing power was greatly reduced4 ,moreover1 it is known that conditions favourable to the fixation of nitrogen by ,azotobacter in cultures on the whole favour nitrogen fixation in soils4 ,the conditions that favour other aerobic nitrogen-fixing bacteria are1 however1 not sufficiently distinct to make such evidence of great value4 ,it is usually found that nitrogen fixation is most active in well-aerated soil4 ,thus ,ashby1#a at ,rothamsted1 found the nitrogen-fixing power of a soil to decrease rapidly with depth4 ,similar results were obtained in ,utah by ,greaves4 ,this suggests1 at first sight1 that anaerobic nitrogen fixers are unimportant under normal soil conditions4 ,it is1 however1 quite possible that they may assume an importance when acting in conjunction with aerobic organisms4 ,thus ,omelianski and ,salunskov#ee found that beneficial association1 or symbiosis1 could occur between ,azotobacter and ,clostridium pasteurianum1 the former absorbing oxygen from the surroundings1 and thus creating a suitable anaerobic environment for the ,clostridium4 ,the question of symbiosis of nitrogen-fixing bacteria with each other and with other organisms offers an inviting field for research4 ,there is evidence that this factor may have considerable importance4 ,beijerinck and ,van ,delden#c early recognised that ,azotobacter in mixed cultures fixed more nitrogen than in pure cultures4 ,granulobacter1 an organism which they found to be commonly associated with ,azotobacter in crude cultures1 appears to increase its nitrogen-fixing powers 7,krzeminiewski74#da ,it was also found by ,hanzawa#ca that a greater fixation of nitrogen was obtained when two strains of ,azotobacter were grown together4 ,a symbiosis between ,azotobacter and green alg has been described1 and will be further discussed by ,dr4 ,bristol4 ,it is likely that this association may be of importance under suitable conditions on the soil surface where the alg are exposed to light4 ,the combination of elemental nitrogen is an endothermic process which requires a very considerable amount of energy for its accomplishment4 ,this fact is well illustrated by the various commercial processes in use for fixation of atmospheric nitrogen4 ,the nitrogen-fixing bacteria obtain this energy from the carbon compounds in the soil4 ,a number of compounds were compared as sources of energy by ,lhnis and ,pillai1#dg who tested their effect on the amounts of nitrogen fixed by ,azotobacter in culture4 ,it was found that mannitol and the simpler sugars give the best results as sources of energy1 but that other organic compounds can also be used4 ,mockeridge#ea has adduced evidence that ethylene glycol1 methyl-1 ethyl-1 and propyl-alcohol1 lactic1 malic1 succinic1 and glycocollic acids could also be utilised4 ,since so large a part of the organic matter added to soil is in the form of celluloses1 it is of great importance to ascertain how far these compounds and their decomposition products can be utilised in nitrogen fixation4 ,stubble1 corn-stalks and roots1 oak leaves1 lupine and lucerne tops1 maple leaves1 and pine needles may all serve as useful sources of energy to nitrogen-fixing organisms in the soil4 ,pure cellulose cannot apparently be used as a source of energy1 but when acted upon by cellulose decomposing organisms1 it becomes available as a source of energy4 ,hutchinson and ,clayton1 at ,rothamsted1 found that a fixation of nitrogen could be brought about by mixed cultures of ,azotobacter1 and of the cellulose attacking ,spirochta cytophaga1 when grown in cultures containing pure cellulose4 ,it is not known how far cellulose decomposition must proceed to produce an effective source of energy1 nor what are the substances thus produced that are utilised4 ,this point will not be decided until something more is known of the course of changes in the breaking-down of cellulose in the soil4 ,the amount of nitrogen fixed per unit of energy material decomposed varies greatly1 according to the organism and the conditions4 ,winogradsky found that his ,clostridium assimilated #b-c mgs4 of nitrogen per gram of sugar consumed4 ,lipman found that ,azotobacter fixed #ae-bj mgs4 of nitrogen per gram of mannite consumed4 ,illustration3 ,,fig4 #e4 ,caption3 ,azotobacter4 ,decrease in efficiency in ,n fixation with age of culture4 7,koch ,seydel47 ,x-axis3 ,days4 ,y-axis3 ,milligrams of ,nitrogen fixed per gram of dextrose consumed4 ,it is found1 however1 that in liquid culture1 the ratio of nitrogen fixed to carbohydrates oxidised varies according to the age of the culture1 falling off rapidly as the age increases#db 7,fig4 #e74 ,this decreasing efficiency in cultures may be due to the accumulation of metabolic products such as would not occur under soil conditions4 ,indeed1 the efficiency of ,azotobacter in a sand culture has been found by ,krainskii#ci to be considerably greater than in solution4 ,it is thus probable that in soil the nitrogen-fixing organisms are less wasteful of energy material than under the usual laboratory conditions4 ,it is to be hoped that future research will indicate what are the conditions that produce the greatest economy of energy material in nitrogen fixation4 ,the fixation of nitrogen in soil is depressed by the presence of considerable amounts of nitrates4 ,this is1 in all probability1 due to the fact that nitrogen-fixing organisms are able to utilise compounds of nitrogen where these are available4 ,the energy needed to build up amino-acids and proteins from nitrate or ammonia is1 of course1 far less than that required to build up these substances from elemental nitrogen4 ,it is1 therefore1 not surprising that where nitrate is available1 ,azotobacter will use it in preference to fixing atmospheric nitrogen4#e ,,table ,,iii4--,,assimilation ,,of ,,nitrates4 ,,by ,,azotobacter ,,in ,,pure ,,culture--7,bonazzi74 ---------------------------------------- ------------ ,nitrate ,organic ,total and ,nitrogen ,fixed ,nitriteand ,ammonia or ,present4 ,present4 ,lost4 ---------------------------------------- ------------ mgs4 mgs4 mgs4 ,culture with nitrate-- ,at beginning #hee #jgf -- ,after growth #jb #hga -#jd ,culture without nitrate-- ,at beginning -- #jgf -- ,after growth -- #dej #c4gd ---------------------------------------- ------------ 7,growth period--#bd days at #be ,c47 ,the chemical process by which nitrogen is fixed is quite unknown1 although a number of speculative suggestions have been made4 ,the appearance of considerable amounts of amino acids in young cultures of ,azotobacter suggests that these may be a step in the process1 but at present the data are too inconclusive to form a basis for theorising4 ,azotobacter is very rich in phosphorus1 an analysis of the surface growth in ,azotobacter cultures1 made by ,stoklasa1 giving about #fj per cent4 of phosphoric acid in the ash4 ,in cultures it has been found that a considerable amount of phosphate is needed to produce full development4 ,as would be expected1 therefore1 nitrogen fixation in soil is often greatly stimulated by the addition of phosphates4 ,christensen has1 indeed1 found soils where lack of phosphate was the limiting factor for ,azotobacter growth4 ,azotobacter is very intolerant of an acid medium1 and is very dependent on the presence of an available base4 ,in cultures this is usually provided in the form of calcium or magnesium carbonate4 ,gainey#ba found that ,azotobacter occurred in soils having an acidity not greater than ,p,h #fj1 and ,christensen1#g1i in ,denmark1 has found a close association between the occurrence of ,azotobacter in soils and the presence of an adequate supply of calcium carbonate4 ,so close was this association that he devised a technique based on this fact for detecting a deficiency of lime in a soil sample4 ,in addition to the groups already discussed1 there is a remarkable and important group of nitrogen-fixing bacteria that inhabit and can carry on their functions within the root tissues of higher plants4 ,it has been known at least from classical times that certain leguminous plants would1 under suitable conditions1 render the soil more productive4 ,on the roots of leguminos small tubercles are commonly found4 ,these were noted and figured by ,malpighi in the seventeenth century1 and for a long time were regarded as root-galls4 ,as was described in ,chapter ,i41 the true nature of these tubercles was finally elucidated by ,hellriegel and ,wilfarth in #ahhf4 ,as the result of a series of pot experiments1 they made the very brilliant deduction that the ability to fix nitrogen1 possessed by the legumes1 was due to bacteria associated with them in the tubercles4 ,these bacteria were finally isolated and studied in pure culture by ,beijerinck4 ,since then a very great deal of literature has accumulated on the subject of the nodule-producing bacteria1 which it is impossible to deal with in a small space4 ,the nodule organism1 ,bacillus radicicola1 when grown on suitable media1 passes through a number of different changes in morphology4 ,the most connected account of these changes is given in a paper by ,bewley and ,hutchinson4#d ,in a vigorous culture the commonest type is a rod-shaped bacillus which may or may not be motile4 ,as these get older they often become branched1 or irregular in shape1 the formation of these branched forms being perhaps due to conditions in the medium4 ,these irregular forms1 known as 8bacteroids10 are a characteristic type in the nodules4 ,their production in culture media has been found to be stimulated by sugars and organic acids such as would occur in their environment within the host plant4 ,in the older rods and bacteroids the staining material becomes condensed into granules1 and finally the rods disintegrate or break up into coccoid forms4 ,by suitable culture conditions1 ,bewley and ,hutchinson obtained cultures consisting almost entirely of this stage4 ,if such a culture be inoculated into a fresh medium rich in sugar1 the swarmer stage appears in great numbers4 ,these swarmers are very minute coccoid rods1 #i #ah in size1 that are actively motile4 ,they apparently develop later into the rod stage4 ,illustration3 ,,fig4 #f4--;,bacillus radicicola4 ,stages in the life cycle4 7,after ,,hutchinson and ,,bewley47 ,motile ,rods ,vacuolated ,stage 8,swarmers0 8,bacteroids0 8,pre-swarmers0 ,very little is known as to the life of the organism in the soil4 ,it is able1 however1 to fix nitrogen in cultures1 and it has been claimed#ce1dh that it can do so in the soil outside the plant1 so that it is possible that we must take it into consideration in this connection4 ,more knowledge is needed as to the optimum conditions for the growth of the organism in the soil4 ,it seems to be more tolerant of acid soil conditions than ,azotobacter4 ,the limiting degree of acidity has been found to vary among different varieties of the organism from ,p,h #cae to ,p,h #di4 ,a long controversy has been held as to whether the nodule organisms found in different host-plants all belong to one species1 or whether there are a number of separate species1 each capable of infecting a small group of host-plants4 ,as the term 8species0 has at present no exact meaning when applied to bacteria1 the discussion in this form is unlikely to reach a conclusion4 ,the evidence seems to show that the nodule organisms form a group that is in a state of divergent specialisation to life in different host-plants1 and that this specialisation has reached different degrees with different hosts4 ,thus the organisms from the nodule of the pea 7,pisum sativum7 will also produce nodules on vicia1 ,lathyrus1 and ,lens1 but seem to have lost the ability normally to infect other legumes4 ,on the other hand1 the bacteria from the nodules of the ,soy ,bean 7,glycine hispida7 have become so specialised that they do not infect any other genus of host-plant1 and soy beans are resistant to infection by other varieties of the nodule organism4 ,burrill and ,hansen1#f after an extensive study1 divided the nodule bacteria into eleven groups1 within each of which the host-plants are interchangeable4 ,the existence of different groups of nodule organisms has been confirmed by the separate evidence of serological tests 7,zipfel1 ,klimmer1 and ,kruger74#dj ,the results of cross-inoculation tests have sometimes been conflicting4 ,it seems1 indeed1 that the host-plant has a variable power of resisting infection1 so that when its resistance is lowered it may be capable of infection by a strange variety of the nodule organism4 ,the question that has thus arisen of the ability of the legume to resist infection is of fundamental importance1 and its elucidation should throw light on the relation of plants to bacterial infection as a whole4 ,the stage of the organism that infects the plant is not at present known4 ,it may be supposed that it is the motile 8swarmer40 ,the entry is normally effected through the root-hairs4 ,the hair is attacked close to the tip1 and an enzyme is apparently produced which causes the tip to bend over in a characteristic manner4 ,the organisms multiply within the root hair and pass down it1 producing a characteristic gelatinous thread filled with bacteria1 in the rod form4 ,this 8infection thread0 passes down into the cells of the root tissue1 where it branches profusely4 ,in young stages of nodule formation the branches can be seen penetrating cells in the pericycle layer4 ,rapid cell division of these root cells is induced4 ,in the course of this cell division abnormal mitotic figures are sometimes found1 such as occur in pathological growths4 ,the cells push outward the root cortical layer1 and so form a nodule4 ,certain of the cells in the centre of the nodule become greatly enlarged1 and in the fully grown nodule are seen to be filled with bacteria4 ,differences have been described in the morphology of the organisms in different parts of the nodule4#fb ,whether the different stages of the organism are equally capable of fixing nitrogen1 or what is the significance of these stages within the nodule1 is not certainly known4 ,it has been held that it is the irregular bacteroid forms that are chiefly concerned with nitrogen fixation4 ,in older nodules the organisms become irregular and stain faintly1 and the bacteroidal tissue breaks down1 the nodule finally decaying4 ,in the fixation of nitrogen that occurs in the nodules1 the bacteria without doubt derive the necessary energy from the carbohydrates of the host-plant4 ,there is evidence that the plant assists the process of fixation by removing soluble metabolic products from the neighbourhood of the bacteria4 ,golding#bb was able to obtain a greatly increased fixation of nitrogen in artificial cultures by arranging a filtering device so as to remove the products of metabolism4 ,the great practical importance of leguminous crops in agriculture has led to numerous attempts being made to increase their growth1 and the fixation of nitrogen in them1 by inoculating the seed or the soil with suitable nodule-bacteria4 ,this inoculation can be effected either with soil in which the host-plant has been successfully grown1 and which should consequently contain the organism in fair numbers1 or else pure cultures of the organisms isolated from nodules may be used4 ,very varying results have been obtained with inoculation trials4 ,in farm practice a leguminous crop has often been introduced into a new area where it has never previously grown4 ,in such soil it is very probable that varieties of the nodule organism capable of infecting the roots may not exist4 ,in such cases inoculation with the right organism or with infected soil often produces good results4 ,the more difficult case1 however1 is that in which the legume crop has been grown for a long time in the locality1 and where the soil is already infected with right organisms4 ,this1 the more fundamental problem1 applies especially to this country4 ,here it would seem that inoculation with a culture of the organism will benefit the plant only 7#a7 if the naturally occurring organisms are present in very small numbers2 or 7#b7 if the organisms in the culture added are more virulent than those already in the soil4 ,the problem of successful inoculation would therefore seem to be bound up with that of grading up the infective virulence of the organism to a higher level4 ,successful nodule development in a legume crop is also dependent to a large degree on the soil conditions4 ,the effects of soil conditions on nodule development have been studied by numerous workers4 ,moisture has been found very greatly to affect the nodule development4 ,certain salts have a very definite effect on nodule formation4#fd ,their effect on the number of nodules developing has been studied1 but the reason for this effect is unusually difficult to decide4 ,the action is usually a complex one4 ,thus phosphates are known to stimulate nodule formation4 ,they probably act in several ways4 ,in the first place1 they may cause the nodule organisms to multiply in the soil2 in the second place1 they produce a greater root development in the plant1 thus increasing the chances of infection2 and in the third place1 ,bewley and ,hutchinson#d have found that phosphates cause the appearance of the motile stage of the organism in cultures4 ,a real understanding of the influence of environment on nodule production will produce great improvements in our methods of legume cropping4 ,d4 ,,the ,,relation ,,of ,,bacterial ,,activities ,,to ,,soil ,,fertility4 ,the various activities of the soil bacteria have a vital importance to the growth of higher plants1 which are dependent for their existence on certain of these processes4 ,in the first place1 as we have seen1 bacteria decompose the tissues of higher plants and produce humus materials1 which are essential to the maintenance of good physical properties in the soil4 ,then the nitrate supply on which most higher plants depend is produced by the decomposition of organic nitrogen compounds by bacteria in their search for energy4 ,the depletion of the total nitrogen content of the soil through rain and through the removal of nitrogen in the crops1 is to some extent compensated by the fixation of atmospheric nitrogen by certain bacteria4 ,on the other hand1 in the assimilation of nitrogen compounds to build up protein1 the bacteria are competing with higher plants for one of their essential food constituents1 and their action may1 under certain conditions1 cause a temporary nitrogen starvation4 ,one must remember1 however1 that large quantities of nitrate are lost from field soils by washing-out through rain action1 especially in winter4 ,the assimilation of nitrate and ammonia by micro-organisms keeps some of this nitrogen in the soil1 and at certain periods may thus be beneficial4 ,there is another important respect in which soil bacteria influence plant growth4 ,their activities result in the release of inorganic salts1 such as potash and phosphates1 in a form available for the use of plants4 ,the release of phosphorus and potassium compounds takes place in two ways4 ,in the first place1 organic matter containing phosphorus and potassium1 in an insoluble form1 is attacked by bacteria1 resulting in these elements being set free as inorganic salts available to the higher plant4 ,secondly1 much of the phosphorus supplied to the soil from rock minerals is present as insoluble phosphates1 such as apatite and iron phosphate4 ,much of the potassium1 too1 is derived from insoluble silicate minerals4 ,in both cases the conversion of the insoluble minerals into soluble phosphates and potassium compounds is brought about to a large extent by solution in water containing carbonic and other acids4 ,these acids are largely produced by micro-organisms1 which1 in addition to carbonic acid1 produce organic acids1 and in specialised cases1 sulphuric and nitrous acids4 ,it has been found1 for example1 that in a compost of soil with sulphur and insoluble phosphate1 sufficient sulphuric acid may be produced by the oxidation of the sulphur by bacteria to convert an appreciable amount of phosphate into a soluble form4 ,when we consider the functions performed by soil bacteria1 therefore1 it is not surprising to find that high bacterial activity in the soil is associated1 as a rule1 with fertility4 ,e4 ,,changes ,,in ,,bacterial ,,numbers ,,and ,,activities1 ,,and ,,their ,,relation ,,to ,,external ,,factors4 ,the object of soil bacteriologists is to discover means of favouring the activity of soil bacteria1 especially those activities that are useful to the higher plant4 ,knowledge is therefore needed of the changes in numbers and activities of the soil bacteria1 and of the influence of soil conditions on them4 ,the necessity of studying these changes has required the development of a quantitative technique by which the numbers of bacteria in the soil and their activities can be estimated4 ,the method commonly used in counting bacteria in soil is a modification of the plating method of ,koch4 ,in counting bacteria two difficulties have to be overcome--their immense numbers and their small size4 ,the numbers of bacteria in soil are so large that the bacterial population of a gram of soil could not1 of course1 be counted directly4 ,the method adopted1 therefore1 is to make a suspension of soil in sterile salt solution1 and to dilute this suspension to a convenient and known extent1 which will depend on the numbers of bacteria expected4 ,in ordinary field soils it is found convenient1 for example1 to dilute the soil suspension so that one cubic centimeter of the diluted suspension will contain #a_/bej1jjjth of a gram of soil4 ,such a volume will commonly contain a number of bacteria sufficiently small to count4 ,the second difficulty is that the organisms are microscopic1 and yet cannot be readily counted under the microscope owing to the presence of soil particles in the suspension4 ,hence recourse is had to plating4 ,one cubic centimeter of diluted suspension is placed in a petri dish and mixed with a suitable nutrient agar medium1 melted1 and cooled to about #dj ,c4 ,the medium sets1 and after a few days' incubation the organisms multiply and produce colonies visible to the naked eye4 ,by counting these colonies we obtain an estimate of the number of bacteria in the one cubic centimeter of suspension1 it being assumed that every organism has developed into one colony1 and by multiplying this number by the degree of dilution we obtain the numbers per gram of soil4 ,in practice a number of parallel platings are made from one cubic centimeter portions of the diluted suspension and the mean number of colonies per plate is taken4 ,by this means the error due to the random distribution of bacteria in the suspension is reduced1 because of the greater number of organisms counted4 ,in drawing conclusions from bacterial count data1 it is necessary to distinguish between the indication which the method gives of the absolute numbers of bacteria in the soil and the accuracy with which it enables the numbers of two soil samples to be compared4 ,the method cannot be used for the former purpose at present4 ,we do not know how far the figures obtained by this counting method fall short of the actual number of bacteria in the soil4 ,one reason for this is the difficulty of effecting a complete separation of the clumps of bacteria into discrete individuals in the suspension4 ,then again1 there is no known medium upon which all the physiological groups of bacteria will develop and produce colonies4 ,and even on a suitable medium some of the individuals may fail to multiply4 ,in comparing the bacterial numbers in two soil samples1 however1 the case is different4 ,within each bacterial group investigated the plate method should give counts proportional to the bacterial numbers in the soil4 ,thus1 by the method one should be able to tell whether the bacterial numbers are increasing or decreasing over a period of time1 or whether a certain soil treatment produces an increase or a decrease4 ,with this end in view the technique of the method has been improved by recent workers4 ,it was found that1 when carefully standardised1 the process of dilution of the soil could be carried out without significant variation in result 7,table ,,iv471 and that the accuracy of the method is limited mainly by the variation in colony numbers on parallel platings1 due in part to random distribution of bacteria throughout the final suspension1 and partly to the uneven development of colonies on the medium4 ,the question of the medium was therefore taken up with a view to improving the uniformity of results obtained with it4 ,lipman1 ,conn1 and others effected an improvement by using chemical compounds as nutrient ingredients1 thus making their media more closely reproducible4 ,on most agar media1 an important disturbing factor is the growth of spreading colonies1 which prevent the development of some of the other colonies4 ,a medium has been devised at ,rothamsted on which these spreading organisms are largely restricted4#fa ,a statistical examination#ai has shown that on this medium errors due to the uneven development of colonies1 except in special cases1 are prevented1 so that in fact the variation in colony numbers between parallel plates is found to be that produced merely by random distribution of bacteria in the diluted suspension 7see ,table ,,iv474 ,in this case the accuracy of the counts of the bacteria in the diluted suspension depend directly on the number of colonies counted1 and can be known with precision4 ,,table ,,iv4--,,bacterial ,,counts ,,of ,a ,,soil ,,sample4 ,,parallel ,,plate ,,counts ,,from ,,four ,,sets ,,of ,,dilutions ,,made ,,by ,,different ,,workers4 ---------------------------------------- -- ,counts of ,colonies on each ,plate4 -------------------------------------- ,plate4 ,set ,i4 ,set ,,ii4,set ,,iii4 ,set ,,iv4 -------------------------------------- #a #gb #gd #gh #fi #b #fi #gb #gd #fg #c #fc #gj #gj #ff #d #ei #fi #eh #fd #e #ei #ff #eh #fb #f #ec #eh #ef #eh #g #ea #eb #ef #ed -------------------------------------- ,mean #fjhf #fehf #fdbh #fbhf -------------------------------------- ,standard deviation between the four sets #efb4 ,standard deviation between plates within the sets #ggf4 ,the knowledge obtained from counts of soil bacteria is subject to another serious limitation4 ,we do not know which of the bacteria counted are the most effective in bringing about the various changes that take place in the soil4 ,it is not even known which of them are active in the soil and which are in a resting condition4 ,it is thus possible to have two soils containing equal numbers of bacteria but showing widely different biochemical activity1 if one soil contains organisms of a higher efficiency4 ,moreover1 as has been pointed out1 many important groups of soil bacteria do not develop on the plating media1 and so are not counted4 ,these considerations led to the development of supplementary methods by which it was hoped to estimate the actual biochemical activity of the soil microflora4 ,the first of these methods was developed by ,remy1 who attempted to study the biochemical activity of a soil by placing weighed amounts into sterile solutions of suitable and known composition1 keeping them under standard conditions for a definite time and then estimating the amount of the chemical change that was being studied4 ,thus1 to test the activity of the organisms that produce ammonia from organic nitrogen compounds1 he inoculated soil into #a per cent4 peptone solution and measured the amount of ammonia produced in a given time4 ,by similar methods the power of a soil to oxidise ammonia to nitrate1 to reduce nitrate1 or to fix atmospheric nitrogen1 is tested4 ,this method has been extensively used and developed by more recent workers4 ,it suffers1 however1 from the same serious disadvantage that it was designed to avoid1 for we cannot be certain that those bacteria that develop in the nutrient solution are the types that are active in the soil1 and1 moreover1 even where the same types do function in the two conditions1 we do not know that the degree of their activity is the same in soil and in solution cultures4 ,for instance1 ,nitrosomonas appears to show very different degrees of activity in soil and in culture4 ,another method1 therefore1 of studying the activity of soil micro-organisms is the obvious one of estimating the chemical changes that they produce in the soil itself4 ,this method has obvious advantages over the unnatural methods developed from ,remy's1 but it has a number of limitations that make its actual application difficult4 ,in the first place1 we cannot always tell whether changes found to occur in soil are due to the activity of micro-organisms1 or are purely chemical reactions unassisted by biological agencies4 ,then1 if we succeed in showing that the changes are due to micro-organisms1 it is very difficult to determine which organisms are effecting them4 ,this cannot be definitely tested by isolating suspected organisms and testing their activity in sterile soil1 because in sterilising soil its nature and composition is altered4 ,in spite of these difficulties1 however1 the study of the chemical changes that take place in the soil has produced valuable knowledge1 when it has been combined with a study of the changes in the number and variety of the micro-organisms that accompany these reactions4 ,this method of investigation is well illustrated by the work of ,russell and ,hutchinson on the effects of heat and volatile antiseptics on soil1 where a study of the chemical changes such as ammonia production1 that occurred in these treated soils1 combined with a study of the changes in bacterial numbers1 led to the realisation that the soil micro-population was a complex one1 containing active protozoa4 ,a great difficulty in applying quantitative methods to bacteria in the field is the great variation in the density of the bacterial population over a plot of field soil1 which may be so great that a bacterial count from a single sample is quite valueless4 ,for example1 the distribution of bacterial numbers over a plot of arable soil near ,northampton was studied by taking sixteen samples distributed over an area about #ab feet square4 ,the result showed that in some cases the bacterial numbers in samples taken #f inches apart differed by nearly #ajj per cent4 ,fortunately1 under favourable conditions1 a remarkably uniform distribution of bacterial numbers over a plot of soil can be found4 ,on such a plot it is possible to investigate the rapidity with which the numbers of the soil micro-organisms alter in point of time4 ,for example1 on the dunged plot of ,barnfield1 ,rothamsted1 which has been cropped with mangolds for forty-seven successive years1 the area distribution of bacteria has been found to be so uniform that if a number of samples of soil are taken from the plot at the same time1 the difference in bacterial numbers between the samples cannot be detected by means of the counting technique 7see ,table ,v474 ,the work of ,cutler1 ,crump1 and ,sandon#af on this plot showed that the bacterial numbers vary very greatly from one day to the next1 and that these fluctuations took place over the whole plot1 since two series of samples1 taken in two rows #f feet apart1 showed similar fluctuations 7see ,fig4 #g74 ,the discovery of these big daily fluctuations in numbers led to an inquiry as to how quickly bacterial numbers change1 and samples from ,barnfield1 taken at two-hourly intervals1 showed that significant changes in numbers took place even at such short intervals4 ,,table ,v4--,,bacterial ,,counts ,,of ,,four ,,soil ,,samples4 ,,from ,,barnfield1 ,,taken ,,simultaneously4 ---------------------------------------- -------------- ,counts of ,colonies on each ,plate4 ---------------------------------------- ---------- ,plate4 ,sample ,i4 ,sample ,,ii4,sample ,,iii4 ,sample ,,iv4 ---------------------------------------- ---------- #a #ch #de #dc #bg #b #cb #dj #cd #da #c #eb #de #eb #ce #d #cb #ca #ee #cf #e #dj #dc #ch #de ,mean #chh #djh #ddd #cfh ---------------------------------------- ---------- ,standard deviation between the four samples #gbe4 ,standard deviation between parallel plates within the sets #gee4 ,illustration3 ,,fig4 #g4 ,x-axis 7top73 ,days4 ,y-axis 7left73 7,series ,a7 ,bacteria--millions per gramme of soil4 ,y-axis 7right73 7,series ,b7 ,bacteria--millions per gramme4 ,caption3 ,daily changes in bacterial numbers in field soil4 ,counts from two series of soil samples taken #f feet apart4 7,after ,cutler47 ,since the bacteria involved in this fluctuation are of great importance to the crops1 being for the most part ammonia producing types1 further knowledge as to the cause of this fluctuation and of its effect on the ammonia and nitrate in the soil is of fundamental importance4 ,there is evidence1 which will be discussed later1 that the cause is connected with the changing activities of certain soil protozoa1 since the daily changes in the numbers of active amb in the soil have been found to be in the reverse direction to those of the bacterial numbers4 ,it appears1 therefore1 that we are dealing with an equilibrium between the various members of the soil population1 the point of equilibrium changing at frequent intervals4 ,in addition to daily changes1 it is possible to detect changes in the numbers and activity of the soil population related to the season4 ,there is a well-marked increase in the spring and autumn 7see ,figs4 #ae1 #af1 pp4 #hi1 #ij74 ,this is well seen when the fortnightly averages of the daily bacterial and protozoal counts from ,barnfield soil are plotted4 ,these spring and autumn increases comprise both the bacterial and the protozoal population1 and therefore differ from the short time fluctuations in being due1 not to a disturbance of the bacteria-protozoa equilibrium1 but to a general rise in activity of both groups of organisms4 ,when we consider the action of external conditions on the soil bacteria1 the existence of a complex soil population and the interdependence of its members must be borne in mind4 ,changes in external conditions may affect the different components of the population in different ways or to different degrees1 thus upsetting the equilibrium between the various groups4 ,for example1 the addition of a mild aromatic antiseptic to the soil apparently affects the protozoa in such a way as to disturb the bacteria-protozoa equilibrium in favour of the bacteria1 while in some cases the aromatic compound affords a food supply to special bacteria1 causing these to increase1 upsetting the equilibrium between the different bacterial groups4 ,when our knowledge of the effect of external factors on the soil population becomes sufficient1 it will probably be found that in nearly all cases a change in the soil conditions produces some disturbance in the equilibrium between the components of the soil population1 though at present there are only certain examples where this disturbance is a probable explanation of the facts4 ,since bacteria are dependent on adequate supplies of energy and food1 it is to be expected that additions of organic matter or of inorganic food materials will greatly benefit their activities4 ,the effect of added farmyard manure in increasing bacterial activities has been much studied4#bg ,some of the increased bacterial numbers and activities in this case may be due to the addition of bacteria with the manure1 but it is thought that this factor is of less importance than the added energy and food supply which the general soil flora obtain from it4 ,nutritive salts such as phosphates and salts of potassium usually increase the bacterial activities4 ,the effect of alkali salts on soil bacteria has been especially studied in the ,western ,united ,states1 where the existence of alkali in the soil is a serious problem4#bc ,soil bacteria are usually stimulated by small doses of alkali salts that are toxic in higher concentration4 ,as a rule1 chlorides are the most toxic salts1 the electronegative ion playing an important part in the effect of the salt4 ,salts affect bacteria both owing to the changes in osmotic pressure which they produce1 and through their specific action on the bacterial protoplasm4#bf ,when equal weights of various salts are added to soil1 their toxic action on bacteria shows so little association with their respective osmotic pressures that we must conclude that this factor is the less important4 ,there is reason to suppose that the toxic action of salts on bacteria is often connected with an effect of the specific ions on the permeability of the bacterial cell-wall4 ,this conclusion is based on the changes in electrical conductivity of bacterial suspensions in the presence of various salts4#ei ,a definite antagonism between various salts has been found to exist4 ,it is possible that future work in this line may indicate what are the proportions of common electrolytes which will produce a properly 8balanced0 soil solution so that the harmful excess of one salt may be antagonised4 ,certain salts1 such as those of arsenic#bd and manganese1 seem to exercise a stimulating action on bacterial activities2 the causes of this action are not at present understood4 ,the acidity of the soil has an important effect on the bacterial processes4 ,the acidity of soils may increase to such a point that the decomposition of plant tissues by bacteria is hindered1 a peat layer being thus produced4 ,the degree of acidity that is toxic varies very greatly with different soil bacteria1 some of them1 like ,azotobacter and ,nitrosomonas being very intolerant of acidity4 ,the conditions of aeration1 water content1 and temperature are inter-related in field soil4 ,ammonifying organisms are not greatly dependent on aeration1 but this factor is sometimes a limiting one in the case of the very aerobic nitrifying bacteria4 ,hence efficient soil cultivation is beneficial to nitrification4 ,many attempts have been made to correlate the temperature and moisture of field soils with the bacterial numbers and activities4 ,these attempts have given very discordant results4 ,it is generally agreed that a plentiful moisture supply is beneficial4 ,thus ,greaves1 in ,utah1 found the optimum water content for ammonia and nitrate production to be about #fj per cent4 of the water-holding capacity4 ,on the other hand1 ,prescott#ef found that the summer desiccation of soil in ,egypt was followed by increased bacterial activities4 ,fabricius and ,feilitzen1#ah using moor soil1 found a direct relationship between soil temperature and bacterial numbers1 showing that temperature can be a limiting factor under certain conditions4 ,with normal arable soils1 however1 no such direct effect of temperature or moisture can be found#af 7see ,fig4 #h74 ,it has even been found by ,conn#aa that freezing of the soil may cause a marked increase in bacterial numbers4 ,the erratic effects of temperature and moisture on the soil bacteria probably afford instances of a disturbance of the equilibrium between the bacteria and other components of the soil micro-population4 ,thus desiccation and freezing1 though they harmfully affect the bacteria1 may inhibit other micro-organisms to a greater degree1 thus freeing the bacteria from competition4 ,it is in the investigation of this equilibrium1 and of the factors that can control it to our benefit1 that the great advances in soil biology in the future are to be expected4 ,illustration3 ,,fig4 #h4--;,effect of frost on the bacterial numbers in the soil4 7,after ,,conn47 ,x-axis3 ,nov4-,may ,y-axis 7bottom73 ,temperature--,degrees ,c4 ,y-axis 7top73 ,bacteria--,millions per ,gramme of ,soil4 ,,references ,,to ,,chapters ,,ii4 ,,and ,,iii4 #a ,ashby1 ,s4 ,f41 ,journ4 ,agric4 ,sci41 #aijg1 vol4 ii41 p4 #ce4 #b ,beijerinck1 ,m4 ,w41 ,centr4 f4 ,bakt41 #aijj1 ,abt4 ,,ii41 ,bd4 #f1 p4 #a4 #c ,beijerinck1 ,m4 ,w41 and ,van ,delden1 ,a41 ,centr4 f4 ,bakt41 #aijb1 ,abt4 ,,ii41 ,bd4 #i1 p4 #c4 #d ,bewley1 ,w4 ,f41 and ,hutchinson1 ,h4 ,b41 ,journ4 ,agric4 ,sci41 #aibj1 vol4 x41 p4 #add4 #e ,bonazzi1 ,e41 ,journ4 ,bact41 #aiba1 vol4 vi41 p4 #cca4 #f ,burrill1 ,t4 ,j41 and ,hansen1 ,r41 ,illin4 ,exp4 ,sta41 #aiag1 ,bulletin #bjb4 #g ,christensen1 ,h4 ,r41 ,centralblatt4 f4 ,bakt41 #aiae1 ,abt4 ,,ii41 ,bd4 #dc1 p4 #a4 #h ,christensen1 ,h4 ,r41 ,centralblatt4 f4 ,bakt41 #aijg1 ,abt4 ,,ii41 ,bd4 #ag1 pp4 #aji1 #afa4 #i ,christensen1 ,h4 ,r41 and ,larsen1 ,o4 ,h41 ,centralblatt4 f4 ,bakt41 #aiaa1 ,abt4 ,,ii41 ,bd4 #bi1 p4 #cdg4 #aj ,conn1 ,h4 ,j41 ,centralblatt4 f4 ,bakt41 #aiaj1 ,abt4 ,,ii41 ,bd4 #bh1 p4 #dbb4 #aa ,conn1 ,h4 ,j41 ,centralblatt4 f4 ,bakt41 #aiad1 ,abt4 ,,ii41 ,bd4 #db1 p4 #eaj4 #ab ,conn1 ,h4 ,j41 ,journ4 ,bact41 #aiaf1 vol4 i41 p4 #ahg4 #ac ,conn1 ,h4 ,j41 ,journ4 ,bact41 #aiag1 vol4 ii41 p4 #acg4 #ad ,conn1 ,h4 ,j41 ,journ4 ,bact41 #aiag1 vol4 ii41 p4 #ce4 #ae ,cramer1 ,e41 ,arch4 f4 ,hyg41 #ahic1 ,bd4 #af1 p4 #aea4 #af ,cutler1 ,w41 ,crump1 ,l4 ,m41 and ,sandon1 ,h41 ,phil4 ,trans4 ,roy4 ,soc41 #aibc1 ,series ,b1 vol4 ccxi41 p4 #cag4 #ag ,doryland1 ,c4 ,j4 ,t41 ,n4 ,dakota ,agr4 ,exp4 ,sta41 #aiaf1 ,bulletin #aaf4 #ah ,fabricius1 ,o41 and ,feilitzen1 ,h41 ,centr4 f4 ,bakt41 #aije1 ,abt4 ,,ii41 ,bd4 #ad1 p4 #afa4 #ai ,fisher1 ,r4 ,a41 ,thornton1 ,h4 ,g41 and ,mackenzie1 ,w4 ,a41 ,ann4 ,appl4 ,biol41 #aibb1 vol4 ix41 p4 #cbe4 #bj ,fred1 ,e4 ,b41 and ,hart1 ,e4 ,b41 ,wisconsin ,agr4 ,exp4 ,sta4 ,research1 #aiae1 ,bulletin #ce4 #ba ,gainey1 ,p4 ,l41 ,journ4 ,agric4 ,research1 #aiah1 vol4 xiv41 p4 #bfe4 #bb ,golding1 ,j41 ,journ4 ,agric4 ,sci41 #aije1 vol4 i41 p4 #ei4 #bc ,greaves1 ,j4 ,e41 ,soil ,sci41 #aiaf1 vol4 ii41 p4 #ddc4 #bd ,greaves1 ,j4 ,e41 ,journ4 ,agric4 ,res41 #aiaf1 vol4 vi1 p4 #chi4 #be ,greaves1 ,j4 ,e41 ,soil ,sci41 #aibj1 vol4 x41 p4 #gg4 #bf ,greaves1 ,j4 ,e41 and ,lund1 ,y41 ,soil ,sci41 #aiba1 vol4 xii41 p4 #afc4 #bg ,greaves1 ,j4 ,e41 and ,carter1 ,e4 ,g41 ,journ4 ,agric4 ,research1 #aiaf1 vol4 vi41 p4 #hhi4 #bh ,groenewege1 ,j41 ,arch4 ,suikerindust41 #aiac1 ,bd4 #ba1 p4 #gij4 #bh;b ,green1 ,h4 ,h41 ,union of ,s4 ,africa ,dept4 ,agr41 ,rept4 of ,director ,vet4 ,res41 #aiah1 p4 #eib4 #bi ,hutchinson1 ,c4 ,m41 ,rept4 ,agr4 ,res4 ,inst4 and ,col4 of ,pusa1 #aiab1 p4 #he4 #cj ,hutchinson1 ,h4 ,b41 and ,clayton1 ,j41 ,journ4 ,agric4 ,sci41 #aiai1 vol4 ix41 p4 #adc4 #cj;b ,hutchinson1 ,h4 ,b41 and ,richards1 ,h4 ,h41 ,journ4 ,min4 ,agric41 #aiba1 vol4 xxviii41 p4 #cih4 #ca ,hanzawa1 ,j41 ,centr4 f4 ,bakt41 #aiad1 ,abt4 ,,ii41 ,bd4 #da1 p4 #egc4 #cb ,hopkins1 ,c4 ,g41 and ,whiting1 ,a4 ,l41 ,ill4 ,agr4 ,exp4 ,sta41 #aiaf1 ,bulletin #aij1 p4 #cie4 #cc ,hoppe-,seyler1 ,g41 ,ztschr4 ,phys4 ,chem41 #ahhf1 vol4 x1 pp4 #bja1 #dja2 #ahhg1 vol4 xi41 p4 #efa4 #cd ,hesselmann1 ,h41 ,skogsvrdsfr4 ,tidskr41 #aiag1 ,no4 #d1 p4 #cba4 #ce ,joshi1 ,n4 ,v41 ,mem4 ,dept4 ,agr4 in ,india1 ,bact4 ,ser41 #aibj1 vol4 i41 ,no4 #i4 #cf ,koch1 ,r41 ,mitt4 ,kais4 ,gesundh41 #ahha1 vol4 i41 p4 #a4 #cg ,kaserer1 ,h41 ,centr4 f4 ,bakt41 #aijf1 ,abt4 ,,ii41 ,bd4 #af1 p4 #fha4 #ch ,kaserer1 ,h41 ,centr4 f4 ,bakt41 #aije1 ,abt4 ,,ii41 ,bd4 #ae1 p4 #egc4 #ci ,krainskii1 ,a4 ,v41 ,centr4 f4 ,bakt41 #aiaj1 ,abt4 ,,ii41 ,bd4 #bf1 p4 #bca4 #dj ,klimmer1 ,m41 and ,kruger1 ,r41 ,centr4 f4 ,bakt41 #aiad1 ,abt4 ,,ii41 ,bd4 #dj1 p4 #beg4 #da ,krzeminiewski1 ,s41 ,centr4 f4 ,bakt41 #aiji1 ,abt4 ,,ii41 ,bd4 #bc1 p4 #afa4 #db ,koch1 ,a41 and ,seydel1 ,s41 ,centr4 f4 ,bakt41 #aiab1 ,abt4 ,,ii41 ,bd4 #ca1 ,p4 #egj4 #dc ,lipman1 ,c4 ,b41 ,bot4 ,gaz41 #aiji1 vol4 xlviii41 p4 #ajf4 #dd ,lipman1 ,c4 ,b41 and ,burgess1 ,p4 ,s41 ,centr4 f4 ,bakt41 #aiad1 ,abt4 ,,ii41 ,bd4 #da1 p4 #dcj4 #de ,lipman1 ,c4 ,b41 and ,burgess1 ,p4 ,s41 ,centr4 f4 ,bakt41 #aiae1 ,abt4 ,,ii41 ,bd4 #dd1 p4 #dha4 #df ,lipman1 ,c4 ,b41 and ,waynick1 ,d4 ,o41 ,soil ,sci41 #aiaf1 vol4 i41 p4 #e4 #dg ,lhnis1 ,f41 and ,pillai1 ,n4 ,k41 ,centr4 f4 ,bakt41 #aijh1 ,abt4 ,,ii41 ,bd4 #bj1 p4 #gha4 #dg;b ,lhnis1 ,f41 and ,smith1 ,t41 ,journ4 ,agric4 ,res41 #aiad1 vol4 vi41 p4 #fge4 #dh ,mackenna1 ,j41 ,rept4 ,prog4 ,agric41 ,india1 #aiag1 p4 #aja4 #di ,marchal1 ,e41 ,bull4 ,acad4 ,roy4 ,belgique1 #ahic1 vol4 xxv41 p4 #gbg4 #ej ,mc,beth1 ,i4 ,g41 and ,scales1 ,f4 ,m41 ,u4,s4 ,dept4 ,ag41 ,bureau ,plant ,indus41 #aiac1 ,bulletin #bff4 #ea ,mockeridge1 ,j41 ,biochem4 ,journ41 #aiae1 vol4 ix41 p4 #bgb4 #eb ,nabokich1 ,a4 ,j41 and ,lebedeff1 ,a4 ,f41 ,centr4 f4 ,bakt41 #aijf1 ,abt4 ,,ii41 ,bd4 #ag1 p4 #cej4 #ec ,nagaoka1 ,m41 ,bull4 ,coll4 ,agr41 ,tokyo1 #aijj1 vol4 vi41 ,no4 #c4 #ed ,omelianski1 ,w4 ,l41 ,comptes ,rendus ,acad4 ,sci41 #ahie1 vol4 cxxi41 p4 #fec2 #ahig1 vol4 cxxv41 pp4 #ijg1 #aaca2 ,arch4 ,sci4 ,bio41 7,st4 ,petersburg71 #ahii1 vol4 vii41 p4 #daa4 #ee ,omelianski1 ,w4 ,l41 and ,sohmskov1 ,m41 ,arch4 ,sci4 ,biol41 ,publ4 ,inst4 ,imp4 ,med4 ,exp4 7,petrograd71 #aiaf1 vol4 xviii41 pp4 #cbg1 #cch1 #dei2 vol4 xix41 p4 #afb4 #ef ,prescott1 ,j4 ,a41 ,journ4 ,agr4 ,sci41 #aibj1 vol4 x41 p4 #agg4 #eg ,shngen1 ,n4 ,l41 ,centr4 f4 ,bakt41 #aije1 ,abt4 ,,ii41 ,bd4 #ae1 p4 #eac4 #eh ,sen ,gupta1 ,n41 ,journ4 ,agr4 ,sci41 #aiba1 vol4 xi41 p4 #acf4 #ei ,shearer1 ,c41 ,journ4 ,hyg41 #aiai1 vol4 xviii41 p4 #ccg4 #fj ,tappeiner1 ,ber4 ,deut4 ,chem4 ,gesell41 #ahhc1 vol4 xvi41 p4 #agcd2 ,zeitsch4 ,biol41 #ahhd1 vol4 xx41 p4 #eb4 #fa ,thornton1 ,h4 ,g41 ,ann4 ,appl4 ,biol41 #aibb1 vol4 ix41 p4 #bda4 #fb ,wallin1 ,i4 ,e41 ,journ4 ,bact41 #aibb1 vol4 vii41 p4 #dga4 #fc ,waksman1 ,s4 ,a41 and ,joffe1 ,j4 ,s41 ,journ4 ,bact41 #aibb1 vol4 vii41 p4 #bci4 #fd ,wilson1 ,j4 ,k41 ,cornell ,agric4 ,exp4 ,sta41 #aiag1 ,bulletin #chf4 ,,chapter ,,iv4 ,,protozoa ,,of ,,the ,,soil1 ,i4 ,that protozoa could be isolated from the soil was a matter of common knowledge to the biologists of the nineteenth century1 but not until the early part of the present century was it suggested that these organisms might be playing some part in the general economy of the soil micro-population4 ,of recent years a great deal of our knowledge of the cytology of the different groups of protozoa1 especially the ,amb1 has been obtained from the study of representatives normally living in the soil2 but unfortunately little or no knowledge has been gained of the biology of these animals in their natural habitat4 ,the view that the presence of these organisms in excessive numbers may lead to 8soil sickness0 was first put forward by ,russell and ,hutchinson in #aiji1 and elaborated in their further papers dealing with 8,partial ,sterilisation of the ,soil40 ,it is unnecessary to discuss in detail this important branch of agriculture1 but to obtain a clear idea of the development of the study of soil protozoa it is necessary to give as briefly as possible the conclusions deduced by ,russell and ,hutchinson from their extensive experiments on soils treated with steam and various volatile antiseptics#ba1bb3-- 87#a7 ,partial sterilisation of the soil causes first a fall1 then a rise1 in bacterial numbers1 which goes on till the numbers considerably exceed those present in the original soil4 87#b7 ,simultaneously there is a marked increase in the rate of accumulation of ammonia which is formed from organic nitrogen compounds4 87#c7 ,the increase in bacterial numbers is the result of improvement in the soil as a medium for bacterial growth1 and not an improvement in the bacterial flora4 87#d7 ,the improvement in the soil brought about by partial sterilisation is permanent1 the high bacterial numbers being kept up even for #bjj days or more4 ,it is evident from 7#c7 and 7#d7 that the factor limiting bacterial numbers in ordinary soil is not bacterial1 nor is it any product of bacterial activity1 nor does it arise spontaneously in soils4 87#e7 ,but if some of the untreated soil is introduced into partially sterilised soil1 the bacterial numbers1 after the initial rise1 begin to fall4 ,thus the limiting factor can be reintroduced from untreated soils4 87#f7 ,evidence of the limiting factor in untreated soils is obtained by studying the effect of temperature on bacterial numbers4 ,untreated soils were maintained at #aj1 #bj1 #cj ,c4 in a well-moistened aerated condition1 and periodical counts were made of the numbers of bacteria per gram4 ,rise in temperature rarely caused any increase in bacterial numbers4 ,but after the soil was partially sterilised the bacterial numbers showed the normal increase with increasing temperatures4 ,,table ,,vi4 ---------------------------------------- ---------------- ,soil ,treated ,untreated ,soil4 with ,toluene4 ,tempera-------------------------------- ----------- ture of ,after,after,after ,after,after,after ,storage4 ,at #ac #be #gj ,at #ac #be #gj ,c4 ,start4,days4,days4,days4,start4,days4,d ays4,days4 ---------------------------------------- ---------- #e-ab #fe #fc #da #cb #he #gc #aja #acg #bj #fe #da #bb #bc #he #ahg #abh #ahb #cj #fe #bg #ej #af #he #aig #ade #ea #dj #fe #ad #i #cc #he #adh #eb #ajj ---------------------------------------- ---------- 87#g7 ,it is evident1 therefore1 that the limiting factor in the untreated soils is not the lack of anything1 but the presence of something active4 ,the properties of the limiting factor are3-- 87a7 ,it is active and not a lack of something4 87b7 ,it is not bacterial4 87c7 ,it is extinguished by heat or poisons4 87d7 ,it can be re-introduced into soils from which it has been extinguished by the addition of a little untreated soil4 87e7 ,it develops more slowly than bacteria4 87f7 ,it is favoured by conditions favourable to trophic life in the soil1 and finally becomes so active that the bacteria become unduly depressed4 8,it is difficult to see what agent other than a living organism can fulfil these conditions4 ,search was therefore made for a larger organism capable of destroying bacteria1 and considerable numbers of protozoa were found4 ,the ciliates and amb are killed by partial sterilisation4 ,whenever they are killed the detrimental factor is found to be put out of action2 the bacterial numbers rise and maintain a high level4 ,whenever the detrimental factor is not put out of action1 the protozoa are not killed4 ,to these rules we have found no exception40 ,from such premises as the above ,russell and ,hutchinson founded the 8protozoa theory of partial sterilisation10 and at ,rothamsted there was commenced the serious study of these soil organisms4 ,goodey was one of the early workers on this new subject1 and added considerably to our knowledge of the species living in normal soils1 and of the chemical constitution of the cyst wall of ciliates4 ,he also made investigations on the effects of various chemicals on the micro-population of soils1 but was unable to draw very definite conclusions4#aa ,one of the first criticisms raised against the protozoa theory of partial sterilisation was that the protozoa were not normal inhabitants of the soil1 and were present only in small numbers1 all of them in the cystic1 quiescent condition4 ,it was further held that these cysts were carried by the wind from dried-up ponds and streams4 ,it is difficult to trace the origin of this view1 since early observers1 viz41 ,ehrenberg and ,dujardin1 in #ahda1 were of the opinion that the protozoa were living in the trophic active condition in the soil1 and it was not until #ahgh that ,stein showed that free living protozoa can encyst4 ,to ,martin and ,lewin1 however1 must be ascribed the distinction of first proving that the soil possesses an active protozoan population1 for by a series of ingenious experiments these observers isolated several flagellates and amb in a trophic condition from certain of the ,rothamsted soils4#ah ,the more recent work in this country has been in the direction of devising new quantitative methods of research1 since by this means alone is it possible to elucidate many fundamental questions4 ,in ,america and elsewhere experiments have been devised for testing the conclusions of ,russell and ,hutchinson4 ,cunningham and ,lhnis1#b in ,america1 ,truffaut and ,bezssonoff1#bd in ,france1 supply evidence in favour of the theory1 but most of the ,american work is in opposition to it4 ,sherman#bc is perhaps the most prominent in opposing the phagocytic action of protozoa on soil bacteria in spite of the fact that certain of his experimental results apparently show enormous decreases in bacterial numbers in the presence of protozoa4 ,in many of his soil inoculation experiments1 however1 it was not demonstrated that his active cultures remained alive after entering the soil4 ,the experimental difficulties of dealing with soil protozoa are considerable1 and without a thoroughly sound technique investigators may easily go astray4 ,,classification4 ,the animal kingdom is divided into two main groups or sub-kingdoms--the ,protozoa and the ,metozoa4 ,in the latter the characteristic feature is that the body is composed of several units1 called cells1 and consequently such animals are often spoken of as multicellular4 ,the ,protozoa1 on the other hand1 are usually designated as uni-cellular1 since their bodies are regarded as being homologous to a single unit or cell of the metozoan body4 ,for various reasons exception has been taken by ,dobell#i and others to the use of the term uni-cellular1 for1 as ,dobell says1 8,if we regard the whole organism as an individual unit1 then the whole protozoan is strictly comparable with a whole metozoon1 and not with a part of it4 ,but the body of a protozoan1 though it shows great complexity of structure1 is not differentiated internally into cells1 like the body of a metozoon4 ,consequently it differs from the latter not in the number of its cellular constituents1 but in lacking these altogether4 ,we therefore define the sub-kingdom of the protozoa as the group which contains all non-cellular animals40 ,it should be pointed out that this view does not find favour with many zoologists1 but it is useful in bringing into prominence the fact that each protozoan is comparable as regards its functions with the multi-cellular animals4 ,the protozoa are again further divided into four main classes3-- ,i4 ,rhizopoda4 ,,ii4 ,mastigophora4 ,,iii4 ,ciliophora4 ,,iv4 ,sporozoa4 ,of the above classes1 representatives of each of the first three are found living in the soil1 but up to the present there is no evidence that any sporozoon is capable of living an active life in the soil1 though the cysts of such organisms may be present4 ,the class ,,rhizopoda consists of those protozoa whose organs of locomotion and food capture are pseudopodia1 that is1 temporary extensions of the living protoplasm4 ,the body is typically naked1 that is to say1 without any cuticular membrane1 though in some forms1 ex4 ,amb terricola1 the external layer of protoplasm is thickened to form a pellicle4 ,a skeleton or shell may be present4 ,the class is further sub-divided into various sub-classes1 only two of which concern the soil protozoologist1 viz41 the ,amb and the ,mycetozoa1 of which the most important representative is ,plasmodiophora brassic1 which attacks the roots of many cruciferous plants1 causing the disease familiarly known as 8,fingers and ,toes40 ,the ,amb are again divided into two orders3-- 7a7 ,nuda1 without shell or skeleton2 7b7 ,testacea1 with shells often termed ,thecamb4 ,representatives of the 8naked0 amb commonly found in soils are ,ngleria 7,dimastigamba7 gruberi1 ,amba diploidea 7possessing two nuclei7 and ,a4 terricola1 the last two forms possessing a comparatively thick skin or pellicles4 ,trinema enchelys1 ,difflugia constricta and ,chlamydophrys stercorea are examples of soil ,thecamb4 ,the class ,,mastigophora consists of those protozoa whose typical modes of progression are by means of flagella1 whip-like filaments which1 by their continual lashing motion1 cause movement of the animal4 ,the body may be naked or corticate4 ,the only organisms which concern the soil biologist belong to the ,flagellata order4 ,the ,flagellates differ considerably among themselves1 both as regards their mode of feeding1 and the number of flagella1 thus making their classification difficult and outside the scope of this book4 ,suffice it to say that in the soil such organisms occur possessing one1 two1 three or four flagella1 ex4 ,oicomonas termo1 ,heteromita globosus1 ,dallengeria and ,tetramitus spiralis4 ,further1 their mode of feeding may be saprophytic in which nourishment is absorbed by diffusion through the body surface in the form of soluble organic substances1 holozoic where solid food particles are taken in1 or holophytic in which food is synthesised by the energy of sunlight4 ,this last group is commonly spoken of as the ,phyto flagellates1 which are to all intents and purposes unicellular alg1 and as such will be dealt with in ,chapter ,,vi4 ,the class ,,ciliophora consists of those protozoa whose typical organs of locomotion are threads or cilia4 ,these organisms can in one sense be regarded as the highest of the protozoa1 since in no other division does the body attain so great a complexity of structure4 ,moreover1 they are typically characterised by a complicated nuclear apparatus with the vegetative and generative portions separated into distinct bodies1 the macro-nucleus and the micro-nucleus4 ,their mode of nutrition is holozoic1 though recently ,peters has brought forward evidence that certain species can obtain their nourishment saprophytically4 ,the sub-class ,ciliata comprises four orders1 all of which are represented in the soil4 ,i4 ,holotricha4 ,the cilia are equal in length and uniformly distributed over the whole body in the primitive forms1 though restricted to special regions in the specialised forms4 ,typical soil forms are ,colpoda cucullus1 ,colpidium colpoda4 ,,ii4 ,heterotricha4 ,there is a uniform covering of cilia1 and a conspicuous spiral zone of larger cilia forming a vibratile membrane and leading to the mouth4 ,,iii4 ,hypotricha4 ,the body is flattened dorso-ventrally and the cilia are often fused to form larger appendages or cirri confined to the ventral surface4 ,movement is typically a creeping one4 ,typical soil forms are ,pleurotricha1 ,gastrostylis1 ,oxytricha4 ,,iv4 ,peritricha4 ,typically of a sedentary habit and the cilia are reduced to a zone round the adoral region of the body4 ,a typical soil form is ,vorticella microstomum4 ,the above classification is far from complete1 but should be sufficient to give an idea of the general grouping of the organisms4 ,for a more detailed account reference must be made to the numerous text books on protozoa4 ,,life ,,histories4 ,the life history of each species has its own characteristic features as regards nuclear division1 etc41 and in many forms1 notably the amb1 it is impossible to identify them with certainty unless the chief stages of the life history are known4 ,in general1 however1 the soil protozoa pass through very similar phases and develop in a perfectly straightforward way4 ,broadly speaking1 there are two main phases of the life history--a period of activity often mistermed vegetative1 and a period of rest4 ,in the former the animal moves1 feeds and reproduces1 while in the latter there is secreted round the body a thick wall1 capable of resisting adverse external influences4 ,this condition is termed the cystic stage1 and by means of it the animals are distributed from place to place by air1 water1 etc4 ,indeed1 so resistant are the cysts that many of them are capable of withstanding the action of the digestive juices of the intestines of animals1 through which they pass to be deposited by the fces on fresh ground4 ,this cystic stage of the life history is found in practically all free-living protozoa1 though it is not formed in exactly the same manner in every case4 ,in the majority of instances the cyst is the product of a single organism1 round which is formed a delicate gelatinous substance which soon hardens and gradually acquires the peculiar characters of the wall4 ,concerning the chemical nature of this wall there is little known1 but ,goodey1#aa working on the cysts of ,colpoda cucullus1 found it to be formed of a carbohydrate1 different from all carbohydrates previously described1 to which the name 8,cytose0 was given4 ,when in this state the animals are able to remain dormant for considerable periods until favourable conditions once more obtain when the wall is ruptured and the animal again resumes the active phase of its life history4 ,this simple process is characteristic of such species as ,heteromita globosus1 ,cercomonas spp41 and many others4 ,it will be noted that no increase of numbers1 i4e4 reproduction1 occurs4 ,a more complex condition is1 however1 sometimes found1 as1 for example1 in the ciliate ,colpoda steinii1 where actual reproduction into small animals takes place within the cyst4 ,finally there is the less common type of cyst formation1 such as is found in the flagellate ,oicomonas termo described by ,martin4#ai ,this flagellate1 in common with all other forms1 reproduces by dividing into two2 the division of the nucleus initiating the process4 ,at certain undetermined periods of the life history1 however1 conjugation occurs between two similar animals forming a large biflagellate body known as the zygote4 ,after swimming about for varying periods of time1 during which the size increases and a large vacuole appears1 the zygote secretes a thick wall1 loses its flagella1 and becomes a cyst4 ,while in this condition the two gamete nuclei fuse to form one1 and eventually a single ,oicomonas emerges from its cyst4 ,similarly in ,a4 diploidea the cysts are formed after two individuals have come together4 ,in the young cysts two amb are found in close association1 and according to ,hartmann and ,ngler#ab a sexual process occurs inside the cyst involving a 8reductive0 division of the nuclei4 ,this requires confirmation1 but it is certain that only one individual comes out of the cysts1 which originally contained two amb4 ,such cysts have been termed by some writers 8reproductive10 evidently a misleading term1 since no increase in numbers1 but rather a decrease1 results from the process4 ,a better term is1 perhaps1 conjugation cyst4 ,in soil protozoa1 then1 three different modes of cyst formation obtain1 and failure to make the distinction inevitably leads to confusion4 ,before leaving the question of life histories1 reference must be made to a peculiar and characteristic feature of ,ngleria gruberi4 ,this amba under certain circumstances assumes a free-swimming biflagellate stage4 ,after variable periods of time the flagella are lost and the ordinary amboid condition resumed4 ,what are the factors concerned in the production of flagellates is unknown1 but flooding the coverslips with distilled water is an effective method for causing their appearance4 ,,distribution ,,of ,,soil ,,protozoa4 ,for both the bacteria and alg observations have been made regarding their distribution through successive depths of the soil2 little can be said1 however1 about the protozoa in this connection4 ,it is certain that they occur throughout the first six inches of the ,rothamsted soils1 though their relative frequencies in the successive inches has not been determined1 but probably they are most abundant in the #bnd to the #dth inch4 ,in this country experiments have not been made to determine whether sub-soil normally contains protozoa2 but from some ,south ,african soil1 taken under sterile conditions #d ft4 down and examined in this laboratory1 large numbers of protozoa were cultivated4 ,this soil1 however1 could not1 for various reasons1 be regarded as a typical sub-soil4 ,kofoid records the presence of ,ngleria gruberi in clay and rock talus taken from the sides of excavations of over #bj ft4 depth1 but the possibility of external infection does not appear to have been excluded4 ,the presence of protozoa is not peculiar to ,british soil since they have been found by various workers in ,germany1 ,france1 the ,united ,states1 and elsewhere4 ,in view of their probable importance in the soil economy there has been instituted a survey of the protozoan species of soil from all parts of the world4 ,this work is in charge of ,mr4 ,sandon1 to whom ,i am indebted for the following summary of his as yet unpublished research4 8,the majority of soil protozoa 7like the fresh-water forms7 appear to be quite cosmopolitan1 for the species found in such widely separated localities as ,england1 ,spitsbergen1 ,africa1 ,west ,indies1 ,gough ,island 7in the ,south ,atlantic7 and ,nauru 7in the ,pacific7 are1 with few exceptions1 identical4 ,this distribution indicates an ability to withstand an extremely wide range of conditions1 for the same species occurring in ,arctic soils1 which are frozen for the greater part of the year1 are found also in soils exposed to the direct rays of the tropical sun4 ,even sand from the ,egyptian desert contains protozoa1 though it seems probable that in such cases they must be present only in the encysted condition for the greater part of the time4 8,not every sample of soil1 however1 contains all the species capable of living in soil1 but the local conditions determining the presence or absence of any species are at present unknown4 ,in general the numbers1 both of species and of individuals present1 follow the number of bacteria4 ,they are consequently most numerous in rich moist soils4 ,the statement sometimes made that protozoa are most numerous in peaty soils is based solely on the number of ,rhizopod shells found in such localities2 but as most of these shells are empty1 their abundance is probably due simply to the slowness with which they disintegrate in these soils where bacterial activity is low1 they do not indicate a great protozoal activity4 ,active protozoa do occur even in extremely acid soils1 but their numbers in such cases are low4 ,the common soil protozoa1 in fact1 appear to be as tolerant of differences in soil acidity as they are of differences in climate1 for many of the same forms which occur in acid soils are found also in soils containing high percentages of chalk4 ,it is possible that some of the less common species may be confined within closer limits of external conditions but the information available on this point is inadequate4 ,all the species1 however1 which in ,rothamsted soils occur in the highest numbers 7e4g4 ,oicomonas termo1 ,heteromita spp41 ,cercomonas crassicauda1 ,ngleria gruberi1 ,colpoda cucullus1 ,c4 steinii7 occur in practically every soil which is capable of supporting vegetation1 though1 of course1 in very varying numbers40 ,it is evident1 therefore1 that the protozoa must be regarded as constituting part of the normal micro-organic population of soils1 and as such are probably playing an important rle4 ,unfortunately our knowledge of the physiology of these organisms is extremely scant1 and much of future research must be directed towards elucidating their functions and their responses to varying environmental conditions4 ,,chapter ,v4 ,,protozoa ,,of ,,the ,,soil1 ,,ii4 ,in the preceding chapter an outline has been given of the development of the study of soil protozoa1 with especial reference to its qualitative aspects4 ,here it is proposed to deal with the quantitative methods which have been devised for studying these organisms and the results obtained4 ,from the beginning great difficulty has been encountered in finding means for counting protozoa2 and most of the early results have been obtained by the use of one of the following methods3 7#a7 direct counts in a known volume of soil suspension by means of a microscope2 7#b7 dilution method as used for counting bacteria1 and suggested by ,rahn1 who made dilutions of the soil and determined1 by examination at periodic intervals1 the one above which protozoa did not grow2 7#c7 ,agar plating as used by ,killer2 7#d7 counting per standard loop of suspension as devised by ,mller4 ,of these the two last have been little used1 and for various reasons are now discarded by most workers4 ,direct methods have been used extensively in the ,united ,states by ,koch#ac and others1#af who claim to have got satisfactory results2 they are1 however1 highly inaccurate and should be discontinued4 ,the present writer#c has shown that there exists a surface energy relationship between the soil particles and the protozoa1 so that the two are always in intimate contact2 thus rendering it impossible to count under the microscope the number of organisms in a given weight of soil suspension 7,fig4 #i74 ,further1 in a clay soil1 such as is found at ,rothamsted1 the clay particles alone make it very difficult to use such methods4 ,the demonstration of this surface energy relationship affords an effective rejoinder to the criticism made against ,russell and ,hutchinson's hypothesis1 viz41 that soil protozoa must be very few in numbers1 since it was impossible to see them on examining soil under the microscope4 ,illustration3 ,,fig4 #i4--,showing the number of amb and flagellates withdrawn from suspensions of varying strengths by different types of solid matter4 ,a clay3 ,b partially sterilized soil3 ,c ignited soil3 ,d fine sand3 ,e waste sand4 ,since complete withdrawal occurs when the numbers of organisms added are less than the capacity of the solid matter1 the first part of each of the above curves is coincident with the ordinate4 ,the numbers of organisms are given in thousands4 7,from ,journ4 ,agric4 ,soc41 vol4 ix47 ,x-axis3 ,number of ,organisms per c4c4 left in ,solution4 ,y-axis3 ,number of ,organisms per c4c4 taken up by ,solid ,matter4 ,the second or dilution method is the one1 therefore1 that has been most extensively developed4 ,cunningham obtained concordant results in this way1 and his method1 modified by ,l4 ,m4 ,crump1 was as follows3 #aj grams of soil were added to #abe c4c4 of sterile tap-water and shaken for three minutes4 ,this gives a #a in #abe dilution4 ,from it further dilutions were made until a sufficiently high one was obtained4 ,petri dishes1 containing nutrient agar1 were inoculated with #a c4c4 of each of the dilutions and incubated4 ,at intervals covering #bh days the plates were examined and the presence or absence of protozoa on each recorded4 ,in this way the approximate number of organisms per gram of soil could be found4 ,by methods essentially similar to this numerous counts have been made of the bacteria and protozoa in field soil and in partially sterilized soils4 ,they were1 however1 inconclusive2 thus1 on the one hand1 ,goodey and several ,american observers1 found no correlation between the numbers of protozoa and bacteria1 while ,miss ,crump and ,cunningham obtained evidence pointing to the reverse conclusion4 ,such divergence of opinion was probably mainly due to two causes3 firstly1 that the time elapsing between the successive counts was too long1 for it has been shown recently that the number of bacteria and protozoa fluctuate very rapidly2 and secondly1 the method was not completely satisfactory since only the total numbers of protozoa were considered1 no means having been found of differentiating between the cystic and active forms4 ,this was a particularly serious source of error for it is possible for soil to contain large numbers of bacteria and protozoa1 of which a high percentage of the latter are in the form of cysts4 ,a count made on such a soil would give results apparently opposed to the theory that protozoa act as depressors of bacteria4 ,this difficulty has1 however1 been overcome by a further modification of the dilution method1 and it is now possible in any soil sample to count both the numbers of cysts and active forms4 ,also a further advance in technique has made it possible to recognise and enumerate the common species of protozoa1 instead of simply grouping them as ,ciliates1 ,flagellates1 and ,amb1 as was done in the past4#g ,briefly the method consists in dividing the soil sample into equal portions 7usually #aj grams each7 one of which is counted1 thus giving the total numbers of protozoa 7active cystic7 present4 ,the second portion is treated over-night with #b per cent4 hydrochloric acid1 the ,h,cl used being ,b4,p4 pure #cah per cent4 ,previous experiments have shown that such acid kills all the active protozoa1 leaving viable the cysts4 ,the number of cysts is therefore found by counting this treated sample1 and the number obtained subtracted from the total gives the active number4,f ,f ,the proof of the accuracy of this method will be found in the following papers3-- 7#a7 ,cutler1 ,d4 ,w4 7#aibj71 ,journ4 ,agric4 ,sci41 vol4 x41 #acf-adc4 7#b7 ,cutler1 ,d4 ,w41 and ,crump1 ,l4 ,m4 7#aibj71 ,ann4 ,app4 ,biol41 vol4 vii41 #aa-bd4 ,the discovery of this method at once puts into the hands of the investigator a much more efficient instrument for studying the activities of the soil micro-population1 especially since at a slightly later date ,thornton's method for counting bacteria was devised4 ,early in #aibj ,cutler and ,crump#f decided to make a preliminary survey of the protozoon and bacterial populations of one of the ,rothamsted field soils 7,broadbalk dunged plot74 ,the investigation was continued for #bh days1 daily soil samples being taken4 ,the results so obtained showed that an extended investigation of the micro-population of field soil would yield interesting and important results1 especially as it was evident that certain views held by soil biologists required modification4 ,in ,july of the same year1 therefore1 it was decided to start an extended investigation of the soil protozoa and bacteria4 ,the method adopted was to make counts of the numbers of bacteria and of six,g species of protozoa in soil samples taken daily direct from the field 7,barnfield dunged plot7 and by statistical methods to correlate these counts one with another and with the data for external conditions4 ,observations at shorter periods than #bd hours could not be made1 but it was found possible to continue the research for #cfe days4#g ,g ,actual counts were made of six species1 though1 as stated on p4 #aj1 observations were made on seventeen4 ,illustration3 ,,fig4 #aj4--;,daily numbers of active amb 7,dimastigamba and ,species 7 and bacteria in #a gram of field soil1 from ,august #bi to ,october #h1 #aibj4 7,from ,phil4 ,trans4 ,roy4 ,soc41 vol4 ccxi47 ,x-axis3 ,august ,september ,october ,y-axis 7left73 ,amoebae ,active numbers per gramme of soil ,y-axis 7right73 ,bacteria in millions per gramme of soil ,legend3 ,dimastigamoeba ,species ,bacteria ,the number of all the organisms showed large fluctuations of two kinds1 daily and seasonal4 ,the size of the changes that took place within so short a period as #bd hours was1 perhaps1 the most surprising fact that the experiment revealed4 ,thus three consecutive samples gave #ehj1 #adbe and #bfbe millions of bacteria per gram respectively2 and the changes exhibited by any of the species of protozoa were at times even larger4 ,this fact is of extreme importance1 since in the past it has always been assumed that the number of bacteria remained fairly constant from day to day1 and investigators have not hesitated to separate the taking of soil samples by long periods4 ,it is now obvious that such a procedure is of little use for comparative purposes 7,fig4 #aj74 ,it has usually been assumed that the changes in the external conditions markedly affect the density of the soil population4 ,to test this the environmental conditions--temperature1 moisture content and rainfall were examined2 but contrary to all expectation no connection could be traced between any of these and the daily changes in numbers of any of the organisms investigated1 and moreover the species of protozoa appeared in the main to be living independently of one another4 ,it is difficult to believe that external conditions are as inoperative as appears from the above2 and in view of the known complexity of the soil it is possible that further research will show that certain combinations of external conditions are important agents in effecting the changes4 ,illustration3 ,,fig4 #aa4--,numbers of active amb 7,dimastigamba and ,species 7 and bacteria to #a gram of field soil for typical periods in ,february and ,april1 #aiba4 7,from ,phil4 ,trans4 ,roy4 ,soc41 vol4 ccxi47 ,x-axis3 ,feby4 ,feby4 ,april ,y-axis 7left73 ,amoebae ,active numbers per gramme of soil ,y-axis 7right73 ,bacteria millions ,legend3 ,dimastigamoeba ,species ,bacteria ,in the case of the bacteria1 however1 the agent causing the fluctuations is mainly the active amb4 ,this was well shown during the year's count1 for with only #ad per cent4 of exceptions1 #aj per cent4 of which can be explained as due to rapid excystation or encystation1 a definite inverse relationship was established between the active numbers of amb and the number of bacteria 7,figs4 #aa and #ab74 ,thus a rise from one day to the next in the ambic population was correlated with a fall in the numbers of bacteria and vice versa4 ,it must not be supposed that the flagellates are of no account in this process2 some species1 known to eat bacteria1 undoubtedly induce slight depressions1 but1 owing to their small size1 any effect is masked by the greater one of the amb4 ,illustration3 ,,fig4 #ab4--,numbers of active amb 7,dimastigamba and ,species 7 and bacteria in #a gram of field soil for typical periods in ,september1 ,october1 and ,november1 #aibj4 ,x-axis3 ,august ,september ,october ,y-axis 7left73 ,amoebae1 thousands ,y-axis 7right73 ,millions1 ,bacteria ,legend3 ,dimastigamoeba ,species ,bacteria ,these experiments seem to admit of no doubt that in field soil the active protozoa are instrumental in keeping down1 below the level they might otherwise have attained1 the numbers of bacteria2 but a further proof of this contention ought to be obtained by inoculation experiments4 ,it should be possible1 by inoculating sterile soil with bacteria alone and with bacteria plus protozoa1 to demonstrate fluctuations in bacterial numbers in the latter1 while those of the former remained constant4 ,this admittedly crucial test has often been tried1 but owing to difficulties in technique1 etc41 has always failed4 ,recently1 however1 by using new methods confirmatory results have been obtained4#e ,ordinary field soil was sterilised by heat at #ajj ,c4 for #a hour on four successive days2 it was then divided into equal portions1 one of which was inoculated with three known species of bacteria1 and the other inoculated with the same number of bacteria plus the cysts of the common soil amba ,ngleria gruberi4 ,the numbers of bacteria in each soil were counted daily for the first eight days and then daily from the #aeth to the #bast day after the experiment started4 ,the results are given in ,table ,,vii4 and ,fig4 #ac4 ,,table ,,vii4 ----------------------------- ,numbers of ,control ,control ,days after 7,bacteria,bacteria ,inoculation4 alone74 ,amb4 ----------------------------- #j #acj #abb #a #dhf #ced #b #igf #aagb #c #abgj #aghd #d #aedh #aedd #e #aifh #aggj #f #badd #aeah #g #aicd #gef #h #afeb #feh #ae #afib #gbh #af #agdh #cjb #ag #agef #ecb #ah #afhd #hbh #ai #afjd #dch #bj #agab #gjh #ba #agfb #bhb ----------------------------- ,the numbers of bacteria are given in millions per gram of soil4 ,illustration3 ,,fig4 #ac4--,numbers of bacteria counted daily in soils containing ,a4 ,bacteria alone4 ,b4 ,same ,bacteria as in ,a ,amb4 ,c4 ,same ,bacteria as in ,a ,flagellates4 7,from ,ann4 ,appl4 ,biol41 vol4 x47 ,it will be noted that the numbers of bacteria in each soil rose steadily until a maximum was reached #f-h days after inoculation4 ,this is in accordance with expectation1 since the reproductive rate of bacteria is much greater than that of the amb1 which1 until their active forms are numerous1 will not exert any appreciable influence on the bacterial population4 ,further1 since the protozoa were inoculated as cysts an appreciable time would elapse before excystation took place4 ,the last seven days of the experiment are of particular interest4 ,during this period the amb were known to be active in the soil1 and were depressing the bacterial numbers1 for in the control 7protozoa-free7 soil the variation in numbers was within experimental error1 while in the other soil the variations were considerable and well outside experimental error4 ,in fact the variations were comparable with those found from day to day in untreated field soils4 ,finally1 the experiment shows that the bacteria in protozoa-free soil are able to maintain high numbers for a longer period than those living in association with protozoa4 ,,seasonal ,,changes4 ,superimposed on the daily variations in numbers there are seasonal changes1 as is clearly shown when fourteen day averages are made of the numbers for each species4 ,bacteria have long been known to show autumn and spring rises1 but recent research has demonstrated that the protozoan population also rises to a maximum at the end of ,november1 with a less marked spring rise at the end of ,march and beginning of ,april 7,figs4 #ad and #ae74 ,it has sometimes been claimed that the numbers of soil organisms are closely linked with the soil moisture1 but no support for this view was found during the course of the experiment4 ,similarly1 as in the case of the daily variations1 no connection could be traced between the seasonal changes and any of the external conditions considered4 ,it is interesting to note1 however1 that the seasonal variations in the numbers of soil organisms is very similar to those recorded for many aquatic organisms4 ,miss ,delf1#h for instance1 found that in ponds at ,hampstead the alg are most numerous in spring and again in the autumn1 and like changes are recorded in ,british lakes by ,west and ,west#be and in the ,illinois river by ,kofoid4#ad ,illustration3 ,,fig4 #ad4--;,fortnightly averages of total numbers of ,oicomonas1 ,species 1 and ,species 1 and of bacteria1 moisture1 and temperature4 7,from ,phil4 ,trans4 ,roy4 ,soc41 vol4 ccxi47 ,x-axis3 ,fortnight beginning #aibj4 ,july4 ,aug4 ,sept4 ,oct4 ,nov4 ,dec4 ,jan #aiba4 ,feby4 ,mch4 ,april4 ,may4 ,june4 ,y-axis 7bottom left73 ,percentage of moisture ,y-axis 7top left73 ,logarithms of numbers of active protozoa per gramme of soil ,y-axis 7bottom right73 ,temperature ,f ,y-axis 7top right73 ,bacteria in millions per gramme ,legend3 ,oicomonas ,species ,species ,bacteria ,temperature ,moisture ,it is difficult to resist the conclusion that these annual variations are produced by similar causes1 from which it follows that the increase in the numbers of protozoa in the soil is not wholly conditioned by an increased food supply--the bacteria--for the alg are not dependent on such a form of nourishment4 ,this is substantiated by the fact that the numbers of protozoa1 except those of ,oicomonas1 rose during ,march1 whereas the corresponding increase in the bacteria was delayed till the early part of ,april4 ,illustration3 ,,fig4 #ae4--;,fortnightly averages of total numbers of ,heteromita1 ,cercomonas1 and ,dimastigamba and of bacteria1 moisture1 and temperature4 7,from ,phil4 ,trans4 ,roy4 ,soc41 vol4 ccxi47 ,x-axis3 ,fortnight beginning ,july #aibj4 ,aug4 ,sept4 ,oct4 ,nov4 ,dec4 ,jan4 #aiba4 ,feb4 ,mar4 ,april ,may ,june ,y-axis 7bottom left73 ,percentage of moisture4 ,y-axis 7top left73 ,logarithms of numbers of active protozoa per gramme of soil4 ,y-axis 7bottom right73 ,temperature ,f ,y-axis 7top right73 ,bacteria in millions per gramme ,legend3 ,heteromita ,cercomonas ,dimastigamoeba ,bacteria ,temperature ,moisture ,owing to the variations in the numbers of both protozoa and bacteria1 little reliance can be placed on figures obtained from an isolated count1 since on one day the total numbers of flagellates may be nearly #b1jjj1jjj per gram and drop by more than half this figure in #bd days4 ,it is certain1 however1 that the numbers recorded in the past are much too low1 since the total flagellate and amb species were lumped together in two groups4 ,some idea of the size of the soil population can be obtained1 nevertheless1 by using the fourteen-day averages mentioned above4 ,in ,table ,,viii4 are tabulated the average total numbers of flagellates1 and amb for the two periods of the year when the population was at its maximum and minimum respectively4 ,an endeavour has also been made to strike a rough balance sheet as to the amount of protoplasm represented by protozoa and bacteria in a ton of soil4 ,for this purpose it has been assumed that the organisms have a specific gravity of #aj and are spheres of diameters1 #f for the flagellates1 #aj for the amb1 and #a for the bacteria2 and that they are uniformly distributed through the top nine inches of soil4 ,the top nine inches of soil is taken as weighing #ajjj tons4 ,,table ,,viii4 ---------------------------------------- ------------------------- ,maximum ,period4 ,minimum ,period4 _/ _/ 7 77 7 ,no4 ,weight ,weight ,no4 per ,weight ,weight per in ,gram in ,tons ,gram4 in ,gram in ,tons ,gram4 per per per per ,gram4 ,acre4 ,gram4 ,acre4 ---------------------------------------- --------------------- ,flagellates #ggj1jjjjjjjjhg #jjhg #cej1jjjjjjjjci #jjci ,amb #bhj1jjjjjjjadg #jadg #aej1jjjjjjjjgh #jjgh ,bacteria #dj1jjj1jjjjjjjjbj #jjb #bb1ejj1jjjjjjjjab #jjab ---------------------------------------- --------------------- ,it must be remembered that the above figures are minimum ones1 as many species of bacteria and protozoa1 known to occur in the soil1 are not included in the statement owing to their not appearing on the media used for counting purposes4 ,illustration3 ,,fig4 #af4--;,daily variations in the numbers of active individuals of a species of flagellate1 ,oicomonas termo 7,ehrenb47 during ,march1 #aiba4 7,from ,phil4 ,trans4 ,roy4 ,soc41 vol4 ccxi47 ,x-axis3 ,march ,y-axis3 ,active numbers per gramme of soil ,before leaving the discussion of daily variations in numbers of protozoa1 reference must be made to the flagellate species4 ,as already mentioned1 their active numbers fluctuate rapidly1 and for the most part entirely irregularly4 ,one species1 however1 ,oicomonas termo1 is characterised by possessing a periodic change2 high active numbers on one day being succeeded by low1 which are again followed by high on the third day4 ,this rhythm was maintained1 with few exceptions1 for #cfe days 7,fig4 #af71 and has been shown to take place in artificial culture kept under controlled laboratory conditions 7,fig4 #ag74 ,illustration3 ,,fig4 #ag4--;,daily variations in the numbers of active individuals of ,oicomonas termo 7,ehrenb47 in artificial culture media kept at a constant temperature of #bj ,c4 ,a1 in hay infusion2 ,b1 in egg albumen4 ,x-axis3 ,days ,y-axis3 ,thousands ,it was thought that an explanation of this phenomenon might be found in alternate excystation and encystation1 since the latter is a constituent part of the animals' life history 7see p4 #gc74 ,this1 however1 does not hold1 for the cyst curve is not the inverse of that of the active2 and1 moreover1 statistical treatment demonstrated that cyst formation is wholly unperiodic in character4 ,an explanation must therefore be sought in the changes in the organisms during the active period of their life1 and the deduction can be drawn that1 increased active numbers tend to be followed by death1 conjugation1 or both1 while decreases in the active numbers are followed by rises in total numbers1 i4e41 reproduction1 and this rhythmically4 ,this somewhat surprising conclusion appears to hold1 in a lesser degree1 for other soil protozoa1 and is of sufficient importance to warrant further research4 ,the direction in which this is being pursued is by a study of the reproductive rates of pure cultures of certain ciliates and flagellates under varying external conditions4 ,space does not admit of adequate discussion of this problem1 but the results already obtained justify the view that such lines of work will elucidate some of the baffling problems of soil micro-biology4 ,,soil ,,reaction4 ,the development of the artificial fertiliser industry has in many ways revolutionised farm practice1 with the inevitable result that new problems have arisen1 not the least of which are biological in character4 ,if1 as seems to be indubitable1 the micro-organisms of the soil are of importance to soil fertility1 it is necessary for us to know in what way this population is affected by the application of fertilisers1 and a start has been made by investigating the effects of hydrogen ion concentration on soil protozoa4 ,much has already been written concerning this question1 but almost entirely on results obtained in artificial cultures4 ,it is always dangerous to argue from the artificial to the natural environment of organisms and particularly so in respect to the soil4 ,also1 as ,collett has shown1 the toxic effects of acids are probably not entirely a function of the hydrogen ion concentration1 but that the molecules of certain acids are in themselves toxic1 an action which can1 however1 be diminished by the antagonistic powers of many substances such as ,na,cl4 ,in this laboratory ,s4 ,m4 ,nasir1 by unpublished work1 has shown that the limiting value on the acid side for ,colpoda cucullus was ,p,h #cc2 for a flagellate 7,heteromita globosus71 #ce2 and for an amba 7,ngleria gruberi71 #ci4 ,also ,mlle4 ,perey1 investigating the numbers of protozoa in one of the ,rothamsted grass plots of ,p,h #cfe1 found a total of #ac1fjj protozoa1 of which #ij per cent4 were active4 ,the tolerance1 therefore1 of these organisms to varying external conditions is greater than has formerly been supposed1 a conclusion which is becoming more evident from the researches mentioned in ,chapter ,,iv4 on soils from different parts of the world4 ,,protozoa ,,and ,,the ,,nitrogen ,,cycle4 ,in partially-sterilised soil from which protozoa were absent ,russell and ,hutchinson obtained an increased ammonia production1 a result also obtained by ,cunningham4 ,hill1 on the other hand1 concluded that protozoa have no effect on ammonification1 but his technique is open to criticism4 ,lipman1 ,blair1 ,owen and ,mc,lean's work#ag contains many figures obtained by adding dried blood1 tankage1 soluble blood flour1 cottonseed meal1 soy-bean meal1 wheat flour1 corn meal1 etc41 to soil4 ,it is difficult to understand how accurate results could be expected when1 to an already little understood complex substance1 such as soil1 is added a series of substances whose effects are practically unknown4 ,free nitrogen-fixation in soils is an important process1 more especially in soils of a light sandy nature1 from which crops are taken year after year without any application of manure4 ,the effect of protozoa on the organisms causing this process has in the past received little attention4 ,recently1 however1 ,nasir#bj has studied the influence of protozoa on ,azotobacter1 both in artificial culture and in sand4 ,from a total of #cf experiments done in duplicate or triplicate1 #ca showed a decided gain in nitrogen fixation over the control1 while only #e gave negative results4 ,illustration3 ,,fig4 #ah4--,showing the highest fixations of nitrogen above the control recorded for ,azotobacter in the presence of different species of ,protozoa4 7,from ,ann4 ,appl4 ,biol41 vol4 ii47 ,x-axis 7left73 ,artificial ,media ,c ,a ,f ,,af ,,ac ,,acf ,x-axis 7right73 ,sand ,cultures ,c ,a ,,af ,,ac ,legend3 ,c represents ,,ciliates4 ,a -do4- ,,amoebae4 ,f -do4- ,,flagellates4 ,as might be expected1 the fixation figures varied from culture to culture1 the highest recorded being #cfjd per cent4 above the control and this in a sand culture 7,fig4 #ah74 ,reference to the details of the experiments shows that the criticisms made against similar work done in the past do not hold here1 and one must conclude that ,azotobacter is capable of fixing more atmospheric nitrogen in the presence of protozoa than in their absence4 ,at present it is impossible to say how this occurs1 but it is highly improbable that the protozoa are themselves capable of fixing nitrogen4 ,a more likely explanation is that the protozoa1 by consuming the ,azotobacter1 kept down the numbers1 and transfer the nitrogen to their own bodies4 ,this will tend to prevent the bacteria from reaching a maximum density1 and reproduction1 involving high metabolism1 will be maintained for a longer period than would have otherwise occurred4 ,this and other possible explanations1 are being tested4 ,little has been said regarding the application of protozoology to the question of soil partial sterilisation4 ,as already pointed out1 in the past much work has been done1 but the results were conflicting4 ,in view1 however1 of our recently acquired knowledge of the life of protozoa in ordinary field soil1 most of the early experiments require repeating4 ,a beginning has already been made1 but the work is not sufficiently advanced to warrant discussion4 ,what is urgently needed1 however1 is to increase our knowledge of the general physiology of these unicellular animals4 ,until we know what are the inter-relationships between the members of the micro-organic population of normal soil it is almost impossible to hope that means will be devised by which they can be controlled4 ,at present we are almost entirely ignorant of the simplest of physiological reactions1 such as the exact effect of various inorganic salts found in the soil4 ,also some experiments in ,germany and the ,states indicate that amb are selective as regards the bacteria they ingest4 ,if this is substantiated it may prove of importance to economic biology4 ,it has been shown that the flagellates occur in the soil in large numbers1 and many of them feed on bacteria4 ,it is probable1 however1 that certain of them feed saprophytically and must therefore exert some influence on the soil solution1 though what this may be is entirely unknown4 ,finally1 as ,nasir has shown1 the protozoa play a part in the complicated nitrogen cycle1 and work of this type needs extending4 ,such1 then1 are a few of the outstanding problems that confront the soil protozoologist2 but he must always remember that the organisms he studies are but a small fraction of the total1 and that any influence affecting one part of the complex will be reflected in another4 ,as ,prof4 ,arthur ,thomson said in his ,gifford ,lectures1 8,no creature lives or dies to itself1 there is no insulation4 ,long nutritive chains often bind a series of organisms together in the very fundamental relation that one kind eats the others40 ,such nutritive chains obtain in the soil as markedly as in other haunts of living creatures4 ,,selected ,,bibliography4 99 ,papers giving extensive bibliographies4 #a ,cunningham1 ,a41 ,journ4 ,agric4 ,sci41 #aiae1 vol4 xvii41 p4 #di4 #b ,cunningham1 ,a41 and ,lhnis1 ,f41 ,centrlb4 f4 ,bakt4 ,abt4 ,,ii41 #aiad1 vol4 xxxix41 p4 #eif4 #c ,cutler1 ,d4 ,w41 ,journ4 ,agric4 ,sci41 #aiai1 vol4 ix41 p4 #dcj4 #d ,cutler1 ,d4 ,w41 ,journ4 ,agric4 ,sci41 #aibj1 vol4 x41 p4 #acf4 #e ,cutler1 ,d4 ,w41 ,ann4 ,app4 ,biol41 #aibc1 vol4 x41 p4 #acg4 #f ,cutler1 ,d4 ,w41 and ,crump1 ,ann4 ,app4 ,biol41 #aibj1 vol4 vii41 p4 #aa4 #g 99 ,cutler1 ,d4 ,w41 ,crump and ,sandon1 ,phil4 ,trans4 ,roy4 ,soc4 ,b41 #aibb1 vol4 ccxi41 p4 #cag4 #h ,delf1 ,e4 ,m41 ,new ,phytologist1 #aiae1 vol4 xiv41 p4 #fc4 #i ,dobell1 ,c4 ,c41 ,arch4 f4 ,protisenk41 #aiaa1 vol4 xxiii41 p4 #bfi4 #aj 99 ,goodey1 ,t41 ,roy4 ,soc4 ,proc4 ,b41 #aiaf1 vol4 lxxxix41 p4 #bgi4 #aa ,goodey1 ,t41 ,roy4 ,soc4 ,proc4 ,b41 #aiac1 vol4 lxxxvi1 p4 #dbg4 #ab ,hartmann1 ,m41 and ,ngler1 ,k41 ,sitz-,ber4 ,gesellsch4 ,naturf4 ,freunde1 #aijh1 ,berlin1 ,no4 #d4 #ac ,koch1 ,g4 ,p41 ,journ4 ,agric4 ,res41 #aiaf1 vol4 li41 p4 #dgg4 #ad ,kofoid1 ,c4 ,a41 ,bull4 ,illinois ,state ,lab4 ,nat4 ,hist41 #aijc and #aijh4 #ae 99 ,kopeloff1 ,n41 ,lint1 ,h4 ,c41 and ,coleman1 ,d4 ,a41 ,centrlb4 f4 ,bakt4 ,abt4 ,,ii41 #aiaf1 vol4 xlvi41 p4 #bh4 #af ,kopeloff1 ,n41 ,lint1 ,h4 ,c41 and ,coleman1 ,d4 ,a41 ,centrlb4 f4 ,bakt4 ,abt4 ,,ii41 #aiaf1 vol4 xlv41 p4 #bcj4 #ag ,lipman1 ,j4 ,g41 ,blair1 ,a4 ,w41 ,owen1 ,l4 ,l41 and ,mc,lean1 ,h4 ,c41 ,n4,j4 ,agric4 ,exp4 ,sta4 #aiab1 ,bull41 ,no4 #bdh4 #ah ,martin1 ,c4 ,h4 and ,lewin1 ,k4 ,r41 ,journ4 ,agric4 ,soc41 #aiae1 vol4 vii41 p4 #ajf4 #ai ,martin1 ,c4 ,h41 ,roy4 ,soc4 ,proc4 ,b41 #aiab1 vol4 lxxxv41 p4 #cic4 #bj 99 ,nasir1 ,s4 ,m41 ,ann4 ,app4 ,biol41 #aibc1 vol4 x41 p4 #abb4 #ba ,russell1 ,e4 ,j41 ,roy4 ,soc4 ,proc4 ,b41 #aiae1 vol4 lxxxix41 p4 #gf4 #bb 99 ,russell1 ,e4 ,j41 8,soil ,conditions and ,plant ,growth10 #aiba1 #dth ed4 #bc 99 ,sherman1 ,j4 ,m41 ,journ4 ,bact41 #aiaf1 vol4 i41 p4 #ce1 and vol4 ii41 p4 #afe4 #bd ,truffaut1 ,g41 and ,bezssonoff1 ,h41 ,compt4 ,rend4 ,acad4 ,sci41 #aibj1 vol4 clxx41 p4 #abgh4 #be ,west1 ,w41 and ,west1 ,g4 ,s41 ,journ4 ,linn4 ,soc4 ,bot41 #aiab1 vol4 xl41 p4 #cie4 ,,chapter ,,vi4 ,,alg4 ,i4 ,,general ,,and ,,historical ,,introduction4 ,speaking broadly1 the organisms of the soil may be classified into several distinct groups differing conspicuously in their general characters and physiological functions and therefore in their economic significance2 among such groups may be mentioned the bacteria1 protozoa1 alg and fungi4 ,it is found1 however1 that though typical members of these groups are conspicuously different from one another1 yet there exist a number of unicellular forms which have characters in common with more than one of these big groups1 and the lines of demarcation between them become difficult to define4 ,it becomes advisable1 therefore1 to depart a little from the systematist's rigid definitions and to adopt a somewhat more logical grouping of the soil organisms based on their mode of life4 ,to give but a single example3 ,euglena viridis occurs quite commonly in soil4 ,through its single flagellum1 its lack of a definite cellulose wall1 its changeable shape and its ability to multiply by simple fission in the motile state it definitely belongs systematically to the group of protozoa4 ,but its possession of chlorophyll1 in enabling it to synthesise complex organic substances from ,,co and water in a manner entirely typical of plants1 connects it physiologically so closely with the lower green alg that in studying the biology of the soil it seems best to include it and other nearly related forms with the alg4 ,on this physiological basis 8soil-alg0 may be defined as those micro-organisms of the soil which have the power1 under suitable conditions1 to produce chlorophyll4 ,such a definition has the advantage that it is wide enough to include the filamentous protonema of mosses1 which1 though alga-like in form and in physiological action1 is nevertheless separated from the true alg by a wide gulf4 ,a more accurate name for such a group of organisms would be the 8chlorophyll-bearing protophyta0 of the soil2 they may be classified briefly as follows 7,table ,,ix473-- ,,table ,,ix4 ---------------------------------------- ------------------------- ,group4 ,colour4 ,pigments4 ---------------------------------------- ------------------------ ,i4,flagellat4 ,euglenace4 ,green4 ,chlorophyll4 ,cryptomonadine4 ,,ii4,alg-- #a4 ,myxophyce4 ,mostly filamen- ,blue-green ,phycocyanin4 tous1 chiefly to violet ,chlorophyll4 ,oscillatoriace or brown4 ,carotin4 and ,nostocace4 #b4 ,bacillariace4,mostly pennate1 ,golden- ,carotin4 chiefly ,navi- brown4 ,xanthophyll4 culoide4 ,chlorophyll4 #c4 ,chlorophyce4 7i7 ,protococ- ,green4 ,chlorophyll4 cales1 ,ulo- trichales1 ,conjugat1 etc4 7ii7 ,heterokont4,yellow- ,chlorophyll4 green4 ,xanthophyll4 ,,iii4,bryophyta4 ,filamentous moss ,green4 ,chlorophyll4 protonema4 ---------------------------------------- ------------------------ ,the importance of the lower alg from a biological standpoint has long been recognised1 since their extremely primitive organisation1 coupled with their ability to synthesise organic compounds from simple inorganic substances1 singles them out as being not very distantly removed from the group of organisms in which life originated upon the earth4 ,but the possibility of their having a very much wider economic significance was completely overlooked until about a quarter of a century ago1 when ,hensen demonstrated their importance in marine plankton as the producers of the organic substance upon which the whole of the animal life of the ocean is ultimately dependent4 ,in consequence1 it has been generally assumed that the growth of alg1 since they contain chlorophyll1 is entirely dependent on the action of light4 ,hence the recent idea of the existence of alg which actually inhabit the soil has been received with a certain amount of scepticism1 though the results of modern physiological research on a number of the lower alg show that there is very good reason to believe that such a soil flora is entirely possible4 ,in considering the alga-flora of a soil it is necessary to distinguish between two very different sets of conditions under which the organisms may be growing4 ,in the first place1 they may grow on the surface of the soil1 being subjected directly to insolation1 rain1 the deposition of dew1 the drying action of wind1 relatively quick changes of temperature and other effects of climate4 ,certain combinations of these conditions present so favourable an environment for the growth of alg that at times there appears on the surface of the soil a conspicuous green stratum1 sometimes so dark in colour as to appear almost black4 ,strata of this nature are well known1 and in systematic works there are constant references to species growing 8on damp soil02 for instance1 of the #ea well-defined species of ,nostoc recognised by ,forte1 no less than #ca are characterised as terrestrial4 ,such appearances1 however1 seem to have been regarded as sporadic and more or less accidental1 rather than as the unusually luxuriant development of an endemic population1 and have been frequently attributed to an excessively moist condition of the soil due to defective drainage4 ,in the second place1 the alg may be living within the soil itself1 away from the action of sunlight and under somewhat more uniform conditions of moisture and temperature4 ,up to the present time the greater number of the investigations carried out in this subject have been of a systematic nature1 and extremely little direct evidence has been obtained which can throw any light on the subject of the economic significance of the soil alg4 ,the earliest systematic work was carried out by ,esmarch1 in #aiaj-aa1 who investigated by means of cultures the blue-green alg of a number of soils from the ,german ,african ,colonies1 the samples being taken from the surface and also from the lower layers of the soil4 ,he obtained a considerable number of species and observed that in cultivated soils they were not confined to the surface but occurred regularly to a depth of #aj-be cms4 and occasionally as low as #dj-ej cms4 ,he attributed their existence in the lower layers to the presence of resting spores carried down in the processes of cultivation1 since his samples from uncultivated soils were unproductive4 ,later1 ,esmarch extended his investigations to a far larger number of samples1 #cie in all1 of soils of different types from ,schleswig-,holstein4 ,he found that blue-green alg were very widely distributed in soils of certain types1 though they occurred rarely in uncultivated soils of low water-content1 and he described no less than #de species of which #cd belonged to the ,oscillatoriace and ,nostocace4 ,certain of the commoner species were obtained from soils of widely different types1 as shown in ,table ,x41 while other forms occurred only rarely and with a much more limited distribution4 ,,table ,x4--,,frequency ,,of ,,occurrence ,,of ,,certain ,,common ,,species ,,in ,,esmarch',s ,,soil ,,samples4 ---------------------------------------- ------------------------- ,percentage of ,samples containing given ,alga4 --------------------------------------- ,uncultivated ,cultivated ,damp ,sandy ,soil4 ,soils4 ----------------------------------- ,shores,shores of of ,sea- ,marsh- ,species4 ,elbe4,lakes4shore4,sandy4,clay4 land4 ---------------------------------------- -------------------- ,anabna variabilis #df #dc #i #ajc #fj #df ,anabna torulosa #ca #adc #fcf #bgf #cdc #efd ,cylindrospermum muscicola #bc #bhf #j #bd #dhf #ei ,cylindrospermum majus #j #adc #j #ch #dj #ccc ,nostoc ,sp4 ,,iii4 #gg #j #j #ch #cg #dhg ---------------------------------------- -------------------- ,taking the number of samples containing blue-green alg as a rough measure of their relative abundance1 ,esmarch obtained the following interesting figures 7,table ,,xi473-- ,,table ,,xi4 ---------------------------------------- --------------- ,percentage of ,samples ,number of ,containing ,samples ,kind of ,soil4 ,blue-green ,alg4,examined4 ---------------------------------------- --------------- ,cultivated marshland #ie #dj ,cultivated clay soil #idf #cg ,uncultivated moist sandy soils #hhf #ce ,cultivated sandy soil #fdd #de ,woodland #abe #dj ,uncultivated,sandy heathland #i #cd ,moorland #j #ce ---------------------------------------- --------------- ,in noting that the soils fell into two groups1 those relatively rich and those poor in blue-green alg1 ,esmarch concluded that the two chief factors governing the distribution of the ,cyanophyce on the surface of soils are1 7#a7 the moisture content of the soil1 7#b7 the availability of mineral salts1 cultivated soils being especially favoured in both of these respects4 ,he further distinguished between cultivated land of two kinds1 viz4 arable land and grass land1 and found that on all types of soil grassland was richer in species than was arable land4 ,esmarch examined1 in addition1 #abi samples taken from the lower layers of the soil immediately beneath certain of his surface samples1 #ajg at #aj-be cms4 and the rest at #cj-ej cms4 depth4 ,in cultivated soils1 whether grassland or arable land1 he found that blue-green alg occurred almost invariably in the lower layers in those places bearing alg on the surface and that1 with rare exceptions1 the alg found in the lower layers corresponded exactly to those on the surface1 except that with increasing depth there was a progressive reduction in the number of species4 ,in uncultivated1 moist1 sandy soils the agreement was far less complete1 for though alg were rarely absent from the lower layers their vertical distribution was frequently disturbed by the action of wind and rain4 ,other uncultivated soils not subject to periodic disturbance were found to be uniformly lacking in alg in the lower layers1 but as the limited number of samples examined came completely from places where there were no alg on the surface this means very little4 ,by direct microscopic examination of soil ,esmarch claims to have found living filaments of blue-green alg at various depths below the surface4 ,he realised1 however1 that there was no indication of the length of time that such filaments had been buried1 and therefore conducted a series of experiments from which he concluded that the period during which the alg investigated could continue vegetatively in the soil after burial varied with different species from #e-ab weeks1 but that during the later part of the period the alg gradually assumed a yellowish-green colour4 ,it is unfortunate that ,esmarch's investigations were directed only towards the blue-green alg since observations made in this country indicate that such a series of records gives but a very incomplete picture of the soil flora as a whole4 ,petersen1 in his 8,danske ,arofile ,alger0 7#aiae7 added considerably to our knowledge of soil alg1 especially of diatoms4 ,unfortunately he confined his investigations of the green alg to forms growing visibly on the surface of the ground4 ,he observed1 however1 that acid soils possessed a different flora from that commonly found on alkaline or neutral soils1 the former being dominated by ,mesotnium violascens1 ,zygnema ericetorum1 and #b spp4 of ,coccomyxa1 while the latter were characterised by ,mesotnium macrococcum var41 ,hormidium1 #b spp41 and ,vaucheria1 #c spp4 ,of diatoms he obtained no less than #bd species and varieties from arable and garden soils1 and five characteristic of marshy soils1 while from forest soils and dry heathland they appeared to be often absent4 ,he omitted all reference to blue-green alg4 ,meanwhile ,robbins1 examining a number of ,colorado soils that contained unprecedented quantities of nitrate1 obtained from them #ah species of blue-green alg1 #b species of green alg1 and one diatom4 ,moore and ,karrer have demonstrated the existence of a subterranean alga-flora of which ,protoderma viride1 the most constantly occurring species1 was shown to multiply when buried to a depth of one metre4 ,in this country attention was first called to the subject by ,goodey and ,hutchinson of ,rothamsted who1 in examining certain old stored soils for protozoa1 obtained also a number of blue-green forms which were submitted to ,professor ,west for identification4 ,this ability of certain algal spores to retain their vitality for a long resting period was so very striking that an investigation was begun at ,birmingham in #aiae to ascertain whether other forms were equally resistant4 ,the investigation was carried out on a large number of freshly collected samples of arable and garden soils which were first aseptically air-dried for at least a month and then grown in culture4 ,no less than #bj species or varieties of diatoms1 #bd species of blue-green and #bj species of green alg were obtained from these cultures 7,table ,,xii474 ,in the majority of the samples there was found a central group of alg1 including ,hantzschia amphioxys1 ,trochiscia aspera1 ,chlorococcum humicola1 ,bumilleria exilis and rather less frequently ,ulothrix subtilis var4 variabilis1 while moss protonema was universally present4 ,these species were thought to form the basis of an extensive ecological plant formation in which1 by the inclusion of other typically terrestrial but less widely distributed species smaller plant-associations were recognised4 ,in certain of the soils1 associations consisting very largely of diatoms were present1 and it is to be noted that the majority of the forms that have been described are of exceedingly small size4 ,it is doubtless this characteristic which enables them to withstand the conditions of drought to which the organisms of the soil are liable to be subjected1 small organisms having been shown to be better able to resist desiccation than are larger ones4 ,since the soil diatoms belong to the pennate type1 they are further adapted to their mode of life by their power of locomotion1 which enables them in times of drought to retire to the moister layers of the soil4 ,in the soils examined in this work blue-green alg were less universally present than were diatoms or green alg1 and the species found appeared to be more local in occurrence4 ,there seemed to be1 however1 an association between the three species1 ,phormidium tenue1 ,ph4 autumnale1 and ,plectonema ,battersii1 at least two of the three species having been found together in no less than #af of the samples1 while all three occurred in #g of them4 ,,table ,,xii4--,,alg ,,in ,,desiccated ,,english ,,soils4 7,,bristol47 ---------------------------------------- ---------------- ,number of ,species4 ,number of ---------------------------- ,samples ,maximum ,average ,group4 ,productive4per ,sample4per ,sample4,total4 ---------------------------------------- -------------- per cent4 ,diatoms #iee #i #cg #bj ,blue-green alg #ggc #g #be #bd ,green alg #ajj #g #dc #bj ,moss protonema #ajj -- -- -- ---------------------------------------- -------------- ,total -- #bj #aje -- ---------------------------------------- -------------- ,it was generally noticeable that those soils found to be rich in blue-green alg contained only a few species of diatoms1 and vice versa4 ,diatoms appeared most frequently in soils from old gardens1 whereas blue-green alg were more characteristic of arable soils4 ,the green alg and moss protonema1 on the other hand1 were distributed universally4 ,the majority of green alg typically found in soils are unicellular1 but a few filamentous forms occur4 ,with the exception of ,vaucheria spp4 these are characterised1 however1 by an ability to break down in certain circumstances into unicellular or few-celled fragments1 in which condition identification is often very difficult4 ,it was also found by cultural examination of a number of old stored soils from ,rothamsted that germination of the resting forms of a number of alg could take place after an exceedingly long period of quiescence4 ,no less than nine species of blue-green alg1 four species of green alg1 and one species of diatom were obtained from soils that had been stored for periods of about forty years1 the species with the greatest power to retain their vitality being ,nostoc muscorum and ,nodularia ,harveyana4 ,,ii4 ,,the ,,soil ,,as ,a ,,suitable ,,medium ,,for ,,algal ,,growth4 ,were it not for the recent advances that have been made in our knowledge of the mode of nutrition of many of the lower alg1 it would be very difficult to account for the widespread occurrence of alg in the soil1 for it is undoubtedly true of some of the more highly evolved alg that their mode of nutrition is entirely typical of that of green plants in general4 ,the application of bacteriological technique to the alg1 however1 by ,beijerinck1 by ,artari1 and by ,chodat and his pupils1 and the introduction of pure-culture methods have led to a study of the physiology of some of the lower alg1 in the hope of getting to understand some of the fundamental problems underlying the nutrition of organisms containing chlorophyll4 ,it is impossible here to do more than mention the names of a few of the more important of those who have worked along these lines1 such as ,chodat1 ,artari1 ,grintzesco1 ,pringsheim1 ,kufferath1 ,nakano1 ,boresch1 ,magnus and ,schindler1 and to condense into a few sentences some of their more important conclusions4 ,it is now established that although in the light the alg are able to build up their substance from ,,co and water containing dilute mineral salts1 yet in such conditions growth is sometimes very slow1 and with some species at any rate it is greatly accelerated by the addition of a small quantity of certain organic compounds4 ,the ability of the lower alg to use organic food materials varies specifically1 quite closely related forms often reacting very differently to the same substance1 but there have been shown to be a considerable number of forms which can make use of organic compounds to such an extent that they can grow entirely independently of light4 ,in such cases the nutrition of the organism becomes wholly saprophytic1 and the chlorophyll may be completely lost2 it has frequently been observed1 however1 that on suitable nutrient media1 even in complete darkness1 certain alg continue to grow and retain their green colour1 provided that a sufficient supply of a suitable nitrogenous compound is present4 ,chlorella vulgaris1 an alga frequently found in soil1 has been shown to be extremely plastic in its relations to food substances4 ,given only a dilute mineral-salts solution as food source1 it absorbs ,,co from the air1 and grows in sunlight with moderate rapidity4 ,the addition of glucose to the medium in the light greatly increases the rate and amount of growth and the size of the cells1 while in the dark the colonies not only remain green but have been shown to develop more vigorously than in full daylight4 ,the organism is also able to use peptone as a source of nitrogen in place of nitrates4 ,stichococcus bacillaris and ,scenedesmus spp41 also occurring in soils1 have been shown to be almost equally adaptable1 though in these cases the organisms grow more slowly in the dark than on the corresponding medium in the light4 ,liquefaction of gelatine by the secretion of proteolytic enzymes has been shown to be a further property of certain species1 resulting in the formation of amino acids such as glycocoll1 phenylalanine1 dipeptides1 etc4 ,this property is1 however1 possessed by only a limited number of species and in varying degree4 ,up to the present very little work of this kind has been done upon alg actually taken from the soil1 and our knowledge is therefore very scanty4 ,of the species so far examined all show considerable increase in growth on the addition to the medium of glucose and other sugars1 and tend to be partially saprophytic2 a few have been shown to liquefy gelatine to some extent4 ,servettaz1 ,von ,ubisch1 and ,robbins have also demonstrated that the protonema of some mosses can make use of certain organic substances1 especially the sugars1 and grow vigorously in the dark4 ,it has been shown1 however1 that light is essential for the development of the moss plant4 ,it was thought at ,rothamsted that some light might be thrown upon the activities of the soil-alg by making counts of the numbers present in samples of soil taken periodically within a circumscribed area4 ,a dilution method similar to that in use in the protozoological laboratory was adopted and applied to samples of arable soil taken from the surface1 and at depths of #b1 #d1 #f and #ab inches vertically beneath4 ,a considerable number of samples were examined in this way from two plots on ,broadbalk wheat-field1 viz43 the unmanured plot and that receiving a heavy annual dressing of farmyard manure4 ,the numbers in the unmanured soil were observed to fall far short of those in that containing a large amount of organic matter1 while in both plots the numbers varied considerably at different times of the year4 ,the chief species in both plots were identical1 and their vertical distribution was fairly uniform1 but it was observed that the numbers of individuals varied according to the depth of the sample4 ,the #fth and #abth inch samples contained very few individuals of comparatively few species1 but the #dth inch samples yielded numbers that were not significantly less than those in the top inch4 ,the #bnd inch sample was usually much poorer in individuals than either the top or the #dth inch4 ,it is unfortunate that this method of counting is not really satisfactory for the alg1 chiefly because it takes no account of the blue-green forms4 ,the gelatinous envelope which encloses the filaments of these alg prevents their breaking up into measurable units4 ,assuming1 as appears to be the case for the two plots investigated1 that the blue-green alg are at least as numerous as the green forms1 the total numbers should probably be at least twice as great as those calculated4 ,taking #ajj1jjj as a rough estimate of the number of alg per gram of manured soil in a given sample1 and assuming the cells to be spherical and of average diameter #aj1 it has been calculated that the volume of algal protoplasm present was at least #c times that of the bacteria though only one-third of that of the protozoa4 ,this is probably only a minimum figure for this sample4 ,a soil population of this magnitude can not be without effect on the fertility of the soil4 ,when growing on the surface of the ground exposed to sunlight the alg must1 by photosynthesis1 add considerably to the organic matter of the soil1 but when they live within the soil itself their nutrition must be wholly saprophytic1 and they can be adding nothing either to the energy or to the food-content of the soil4 ,how these organisms fit into the general scheme of life in the soil is at present undetermined1 and there is a wide field for research in this direction4 ,,iii4 ,,relation ,,of ,,alg ,,to ,,the ,,nitrogen ,,cycle ,probably the most important limiting factor in ,british agriculture is the supply of nitrogen available for the growing crop1 and it seems likely that the soil-alg are intimately connected with this question in several ways4 ,periodic efforts have been made during the last half century to establish the fact that a number of the lower organisms1 including the green alg1 have the power of fixing atmospheric nitrogen and converting it into compounds which are then available for higher plants4 ,this property has been definitely established for certain bacteria1 and rather doubtfully for some of the fungi1 but until recently no authentic proof had been produced that alg by themselves could fix nitrogen4 ,the subject is too wide to be discussed in much detail here4 ,schramm in ,america1 working with pure cultures of alg1 tried for ten years to establish the fact of nitrogen fixation1 and failed completely2 more recently ,wann has extended ,schramm's work1 and claims to have proved indisputably that1 given media containing nitrates as a source of nitrogen and a small amount of glucose1 the seven species of alg tested by him fixed atmospheric nitrogen to the extent of #d-ed per cent4 of the original nitrogen content of the medium4 ,so important a result needed corroboration1 and ,wann's experiment1 with some slight improvements1 was therefore repeated at ,rothamsted last summer4 ,this work has not yet been published1 but in the whole series of ninety-six cultures1 with four different species1 each growing on six different media1 there is no evidence that nitrogen fixation has taken place2 but there has been a total recovery at the end of the experiment of #ihic per cent4 of the original nitrogen supplied4 ,on the other hand1 a flaw has been detected in ,wann's method of analysing those media containing nitrates1 sufficiently great to account for the differences he obtained between the initial and final nitrogen content of his cultures4 ,hence1 though one hesitates to say that the alg are unable1 given suitable conditions1 to fix atmospheric nitrogen1 one must admit that no one has yet proved that they can do so4 ,it is far more likely1 however1 that the experiments of ,kossowitsch and others throw more light on the relation of soil alg to nitrogen fixation4 ,they affirm that greater fixation of nitrogen is effected by mixtures of bacteria and certain gelatinous alg than by nitrogen-fixing bacteria alone1 and that the addition of alg to cultures of bacteria produces a stimulating effect only slightly less than that of sugar4 ,it is probable1 therefore1 that the alg1 in their gelatinous sheaths1 provide easily available carbohydrates from which the bacteria derive the energy essential to their work1 and that nitrogen fixation in nature is due to the combined working of a number of different organisms rather than to the individual action of single species4 ,russell and ,richards have shown that the rate of loss of nitrogen by leaching from uncropped soils is far less than would be expected from a purely chemical standpoint1 and suggest that certain organisms are present in the soil which1 by absorbing nitrates and ammonium salts as they are formed1 remove them from the soil solution and so help to conserve the nitrogen of the soil4 ,it is probable that the soil alg act in this manner1 though to what extent has not yet been determined4 ,,iv4 ,,relation ,,of ,,alg ,,to ,,soil ,,moisture ,,and ,,to ,,the ,,formation ,,of ,,humus ,,substances4 ,in warmer countries than our own1 especially those with an adequate rainfall1 the significance of soil alg is perhaps more obvious to a casual observer4 ,treub states that after the complete destruction of the island of ,krakatoa by volcanic eruption in #ahhc1 the first colonists to take possession of the island were six species of blue-green alg1 viz41 ,tolypothrix sp41 ,anabna sp41 ,symploca sp41 ,lyngbya #c spp4 ,three years after the eruption these organisms were observed to form an almost continuous gelatinous and hygroscopic layer over the surface of the cinders and stones constituting the soil1 and by their death and decay they rapidly prepared it for the growth of seeds brought to the island by visiting birds4 ,hence the new flora which soon established itself upon the island can be said to have had its origin in the alga-flora which preceded it4 ,fritsch has also emphasised the importance of alg in the colonisation of new ground in ,ceylon4 ,welwitsch ascribes the characteristic colour from which the 8pedras negras0 in ,angola derive their name to the growth of a thick stratum of ,scytonema myochrous1 a blue-green alga1 which gradually becomes black and completely covers the soil4 ,at the close of the rainy season this gelatinous stratum dries up very slowly1 enabling the underlying soil to retain its moisture for a longer period than would otherwise be the case4 ,the gelatinous soil alg are probably very important in this respect1 for their slow rate of loss of water is coupled with a capacity for rapid absorption1 and they are therefore able to take full advantage of the dew that may be deposited upon them and increase the power of the soil to retain moisture4 ,v4 ,,relation ,,of ,,alg ,,to ,,gaseous ,,interchanges ,,in ,,the ,,soil4 ,in the cultivation of rice the alg of the paddy field have been found to be of extreme importance4 ,brizi in ,italy has shown that although rice is grown under swamp conditions yet the roots of the rice plant are typical of those of ordinary terrestrial plants and have none of the structural adaptations to aquatic life so characteristic of ordinary marsh plants4 ,hence the plants are entirely dependent for healthy growth upon an adequate supply of oxygen to their roots from the medium in which they are growing4 ,a serious disease of the rice plant1 characterised by the browning and dying off of the leaves1 which was thought at first to be due to the attacks of fungi1 was found to be the effect of the inadequate aeration of the roots1 while the entry of the fungi was shown to be subsequent to the appearance of the physiological disease4 ,the presence of alg in the swamp water was found to prevent the appearance of this disease1 in that they unite with other organisms to form a more or less continuous stratum over the surface of the ground1 and add to the gases which accumulate there large quantities of oxygen evolved during photosynthesis4 ,the concentration of dissolved oxygen in the water percolating through the soil is thereby raised to a maximum1 and the healthy growth of the crop ensured4 ,this work has been corroborated by ,harrison and ,aiyer in ,india1 and a sufficient supply of alg in the swamp water is now regarded as one of the essentials for the production of a good rice crop4 ,from what has been said1 it appears that1 although our knowledge of the soil alg is extremely limited1 and our conception of the part they play is largely based on speculation1 yet the subject is one of enormous interest and worthy of investigation in many directions4 ,in its present undeveloped state1 it is a little difficult to foresee which lines of study are likely to prove most profitable1 but there is little doubt that eventually the soil alg will be shown to play a significant part in the economy of the soil4 ,,selected ,,bibliography4 99 ,papers giving extensive bibliographies4 ,i4 ,,general4 #a ,bristol1 ,b4 ,m41 8,on the ,retention of ,vitality by ,alg from ,old ,stored ,soils10 ,new ,phyt41 #aiai1 xviii41 ,nos4 #c and #d4 #b ,bristol1 ,b4 ,m41 8,on the ,alga-,flora of some ,desiccated ,english ,soils3 an ,important ,factor in ,soil ,biology10 ,annals of ,botany1 #aibj1 vol4 xxxiv41 ,no4 #acc4 #c ,brizi1 ,u41 8,ricerche sulla ,malattia del ,riso detta #8,brusone1' ,sect4 ,,iv4 ,influenza che le alghe verdi esercitano in risaia10 ,annuario dell ,instituzione ,agraria ,dott4 ,a4 ,ponti1 ,milan1 #aije1 vol4 vi41 pp4 #hd-hi4 #d ,esmarch1 ,f41 8,beitrag zur ,cyanophyceen-,flora unserer ,kolonien10 ,jahrb4 der ,hamburgischen wissensch4 ,anstalten1 #aiaj1 xxviii41 #c4 ,beiheft1 ,s4 #fb-hb4 #e ,esmarch1 ,f41 8,untersuchungen ber die ,verbreitung der ,cyanophyceen auf und in verschiedenen ,boden10 ,hedwigia1 #aiad1 ,band lv41 ,heft #d-e4 #f ,fritsch1 ,f4 ,e41 8,the ,rle of ,algal ,growth in the ,colonisation of ,new ,ground and in the ,determination of ,scenery10 ,geog4 ,journal1 #aijg4 #g ,harrison1 ,w4 ,h41 and ,aiyer1 ,p4 ,a4 ,subramania1 8,the ,gases of ,swamp ,rice ,soils10 ,mem4 ,dept4 ,agr4 in ,india1 ,chem4 ,ser4 7,i47 8,their ,composition and ,relationship to the ,crop10 #aiac1 vol4 iii41 ,no4 #c2 7,,ii47 8,their ,utilisation for the ,aeration of the ,roots of the ,crop10 #aiad1 vol4 iv41 ,no4 #a2 7,,iv47 8,the ,source of the ,gaseous ,soil ,nitrogen10 #aiaf1 vol4 v41 ,no4 #a4 #h;a ,hensen1 ,v41 8,ueber die ,bestimmung des ,planktons oder des im ,meere treibenden ,materials am ,pflanzen und ,thieren40 ,fnfter ,ber4 ,komm4 wiss4 ,unters4 deutschen ,meere1 #ahhg4 #h ,moore1 ,g4 ,t41 and ,karrer1 ,j4 ,l41 8,a ,subterranean ,alga ,flora10 ,ann4 ,miss4 ,bot4 ,gard41 #aiai1 vi41 pp4 #bha-cjg4 #i ,nadson1 ,g41 8,die perforierenden 7kalkbohrende7 ,algen und ihre ,bedeutung in der ,natur10 ,scripta bot4 hort4 ,univ4 ,imp4 ,petrop41 #aija1 ,bd4 #ag4 #aj ,petersen1 ,j4 ,b41 8,danske ,arofile ,alger10 ,d4 ,kgl4 ,danske ,vidensk4 ,selsk4 ,skrifter1 #g ,raekke1 ,naturv4 og mathem41 #aiae1 ,bd4 xii41 #g1 ,copenhagen4 #aa ,robbins1 ,w4 ,w41 8,alg in some ,colorado ,soils10 ,agric4 ,exp4 ,sta41 ,colorado1 #aiab1 ,bulletin #ahd4 #ab ,treub1 8,notice sur la nouvelle ,flora de ,krakatau10 ,ann4 ,jard4 ,bot4 ,buitenzorg1 #ahhh1 vol4 vii41 pp4 #bba-bbc4 ,,ii4 ,,relation ,,of ,,alg ,,to ,,light ,,and ,,carbon4 #ac ,artari1 ,a41 8,zur ,ernhrungsphysiologie der grnen ,algen10 ,ber4 der ,d4 bot4 ,ges41 #aija1 ,bd4 xix41 ,s4 #g4 #ad ,artari1 ,a41 8,zur ,physiologie der ,chlamydomonaden 7,chlam4 ,ehrenbergii720 7,i47 ,jahrb4 f4 ,wiss4 ,bot41 #aiac1 ,bd4 lii41 ,s4 #daj2 7,,ii47 ,ibid41 #aiad1 ,bd4 liii41 ,s4 #ebg4 #ae ,adjarof1 ,m41 8,recherches exprimentales sur la ,physiologie de quelques ,algues vertes10 ,universit de ,genve--,institut ,botanique1 ,prof4 ,r4 ,chodat--#aije1 #f serie1 vii4 fascicule1 ,genve4 #af ,beijerinck1 ,m4 ,w41 8,berichte ber meine ,kulturen niederer ,algen auf ,nhrgelatine10 ,centr4 f4 ,bakt4 u4 ,paras41 #ahic1 ,abt4 ,i41 ,bd4 xiii41 ,s4 #cfh1 ,jena4 #ag ,boresch1 ,k41 8,die ,frbung von ,cyanophyceen und ,chlorophyceen in ihrer ,abhngigkeit vom ,stickstoffgehalt des ,substrates10 ,jahrbcher fr ,wiss4 ,botanik41 #aiac1 lii41 pp4 #ade-he4 #ah ,chodat1 ,r41 8tude critique et exprimentale sur le polymorphisme des ,algues10 ,genve1 #aiji4 #ai ,chodat1 ,r41 8,la crsol-tyrosinase1 ractif des peptides et des polypeptides1 des protides et de la protolyse10 ,archiv4 des ,sciences physiques et naturelles1 #aiab4 #bj ,chodat1 ,r41 8,monographie d',algues en ,culture pure3 ,matriaux pour la ,flore ,cryptogamique ,suisse10 #aiac1 vol4 iv41 fasc4 #b1 ,berne4 #ba ,dangeard1 ,p4 ,a41 8,observations sur une ,algue cultive l'obscurit depuis huit ans10 ,compt4 ,rend4 ,acad4 ,sci4 7,paris71 #aiba1 vol4 clxxii41 ,no4 #e1 pp4 #bed-fj4 #bb tard et ,bouilhac1 8,sur la prsence de la chlorophyll dans un ,nostoc cultiv l'abri de la lumire10 ,compt4 ,rend41 t4 cxxvii1 #ahih4 #bc ,grintzesco1 ,j41 8,recherches exprimentales sur la morphologie et la physiologie exprimentale de ,scenedesmus acutus10 ,meyen4 ,bull4 herb4 ,boiss41 #aijb1 ,bd4 ii41 pp4 #bai-fd and #djf-bi4 #bd ,grintzesco1 ,j41 8,contribution l'tude des ,protococcoides3 ,chlorella vulgaris ,beyerinck10 ,revue gnrale de ,botanique1 #aijc1 xv41 pp4 #e-ai1 #fg-hb4 #be 99 ,kufferath1 ,h41 8,contribution la physiologie d'une protococcace nouvelle1 ,chlorella luteo-viridis ,chod4 n4 sp4 var41 lutescens ,chod4 n4 var410 ,recueil de l'institut bot4 ,lo ,errera1 #aiac1 t4 ix1 p4 #aac4 #bf ,kufferath1 ,h41 8,recherches physiologiques sur les algues vertes cultives en culture pure10 ,bull4 ,soc4 ,roy4 ,bot4 ,belgique1 #aiba1 liv41 pp4 #di-gg4 #bg ,magnus1 ,w41 and ,schindler1 ,b41 8,ueber den ,einflusz der ,nhrsalze auf die ,frbung der ,oscillarien10 ,ber4 der ,d4 ,bot4 ,gesellschaft1 #aiab-ac1 xxx41 p4 #cad4 #bh 99 ,nakano1 ,h41 8,untersuchungen ber die ,entwicklungs- und ,ernhrungsphysiologie einiger ,chlorophyceen10 ,journ4 ,college of ,sci4 ,imp4 ,univ4 ,tokyo1 #aiag1 vol4 xl41 ,art4 #b4 #bi ,pringsheim1 ,e41 8,kulturversuche mit chlorophyll-fhrenden ,mikroorganismen10 ,cohns ,beitrge ,z4 ,biol4 d4 ,pflanzen4 7,i47 ,die ,kultur von ,algen in ,agar1 #aiab1 ,bd4 xi41 ,s4 #bdi2 7,,ii47 ,zur ,physiologie der ,euglena gracilis1 #aiac1 ,bd4 xii41 ,s4 #a42 7,,iii47 ,zur ,physiologie der ,schizophyceen1 #aiac1 ,bd4 xii41 ,s4 #ii4 #cj ,radais1 8,sur la culture pure d'une algue verte2 formation de chlorophylle l'obscurit10 ,comptes ,rendus1 #aijj1 cxxx41 p4 #gic4 #ca ,richter1 ,o41 8,zur ,physiologie der ,diatomeen40 7,i47 ,sitzber4 d4 kais4 ,akad4 d4 ,w4 in ,wien1 math1 naturw4 ,kl41 #aijf1 ,bd4 cxv41 ,abt4 ,i41 ,s4 #bg2 7,,ii47 ,denkschrift d4 math4 naturw4 ,kl4 d4 kais4 ,akad4 d4 ,w4 in ,wien1 #aiji1 ,bd4 lxxxiv41 ,s4 #fff2 7,,iii47 ,sitzber4 d4 ,kais4 ,akad41 etc41 #aiji1 ,bd4 cxviii41 ,abt4 ,i41 ,s4 #accg4 #cb ,richter1 ,o41 8,ernhrung der ,algen10 #aiaa4 #cc ,robbins1 ,w4 ,j41 8,direct ,assimilation of ,organic ,carbon by ,ceratodon purpureus10 ,bot4 ,gaz41 #aiah1 lxv41 pp4 #edc-ea4 #cd ,schindler1 ,b41 8,ueber den ,farbenwechsel der ,oscillarien10 ,zeitsch4 f4 ,bot41 #aiac1 v41 pp4 #dig-ege4 #ce ,ternetz1 ,charlotte1 8,beitrge zur ,morphologie und ,physiologie der ,euglena gracilis10 ,jahrb4 f4 ,wiss4 ,bot41 #aiab1 ,bd4 #ea1 ,s4 #dce4 ,,iii4 ,,relation ,,of ,,alg ,,to ,,nitrogen4 #cf ,berthelot1 8,recherches nouvelles sur les microorganismes fixateurs de l'azote10 ,comptes ,rend41 #ahic1 cxvi41 pp4 #hdb-di4 #cg ,bouilhac1 ,r41 8,sur la fixation de l'azote atmosphrique par l'association des algues et des bactries10 ,comptes ,rend41 #ahif1 cxxiii41 pp4 #hbh-cj4 #ch ,bouilhac and ,giustiniani1 8,sur une culture de sarrasin en prsence d'un mlange d'algues et de bactries10 ,comptes ,rendus1 #aijc1 cxxxvii41 pp4 #abgd-gf4 #ci ,charpentier1 ,p4 ,g41 8,alimentation azote d'une algue3 ,le ,cystococcus humicola10 ,ann4 ,inst4 ,pasteur1 #aijc1 #ag1 pp4 #cba-cd4 #dj ,fischer1 ,hugo1 8ber ,symbiose von ,azotobacter mit ,oscillarien10 ,centr4 f4 ,bakt41 #aijd1 xii4 #da ,frank1 ,b41 8,uber den experimentellen ,nachweis der ,assimilation freien ,stickstoffs durch ,erdbewohnende ,algen10 ,ber4 der ,d4 ,bot4 ,gesellsch41 #ahhi1 vol4 vii41 pp4 #cd-db4 #db ,frank1 ,b41 8,ueber den gegenwrtigen ,stand unserer ,kenntnisse der ,assimilation elementaren ,stickstoffs durch die ,pflanze10 ,ber4 der4 ,d4 ,bot4 ,ges41 #ahhi1 vii41 #bcd-dg4 #dc ,frank1 ,b41 and ,otto1 ,r41 8,untersuchungen ber ,stickstoff ,assimilation in der ,pflanze10 ,ber4 der ,d4 ,bot4 ,ges41 #ahij1 viii41 #cca-cdb4 #dd ,gautier and ,drouin1 8,recherches sur la fixation de l'azote par le sol et les vgtaux10 ,compt4 ,rend41 #ahhh1 cvi41 pp4 #aagd-gf2 ,general ,conclusions1 p4 #abcb4 #de ,kossowitsch1 ,p41 8,untersuchungen ber die ,frage1 ob die ,algen freien ,stickstoff fixiren10 ,bot4 ,zeit41 #ahid1 ,heft #e1 ,s4 #ih-aaf4 #df ,krger1 ,w41 und ,schneidewind1 8,sind niedere chlorophyllgrne ,algen imstande1 den freien ,stickstoff der ,atmosphre zu assimilieren und ,boden an ,stickstoff zu bereichern80 ,landwirtschaftliche ,jahrb41 #aijj1 ,bd4 #bi1 ,s4 #gga-hjd4 #dg ,moore1 ,benjamin1 and ,t4 ,arthur ,webster1 8,studies of the photosynthesis in f4w4a40 7,i47 8,the fixation of both ,c and ,n from atmosphere to form organic tissue by green plant cell02 7,,ii47 8,nutrition and growth produced by high gaseous dilutions of simple organic compounds1 such as formaldehyde and methylic alcohol02 7,,iii47 8,nutrition and growth by means of high dilution of ,,co and oxides of ,n without access to atmosphere10 ,proc4 ,roy4 ,soc41 ,london1 #aibj1 ,b4 xci41 pp4 #bja-ae4 #dg;a ,moore1 ,b41 ,whiteley1 ,webster1 ,t4 ,a41 ,proc4 ,roy4 ,soc41 ,london1 ,b41 #aiba2 xcii41 pp4 #ea-fj4 #dh ,reinke1 ,j41 8,symbiose von ,volvox und ,azotobacter10 ,ber4 der d4 ,bot4 ,ges41 #aijc1 ,bd4 xxi41 ,s4 #dha4 #di ,russell1 ,e4 ,j41 and ,richards1 ,e4 ,h41 8,the washing out of ,nitrates by ,drainage ,water from ,uncropped and ,unmanured ,land10 ,journ4 ,agric4 ,sci41 #aibj1 vol4 x41 ,part ,i4 #ej ,schloesing1 fils1 and ,laurent1 ,e41 8,recherches sur la fixation de l'azote libre par les plantes10 ,ann4 de l',institut ,pasteur1 #ahib1 vi41 pp4 #fe-aae4 #ea ,schramm1 ,j4 ,r41 8,the ,relation of ,certain ,grass ,green ,alg to ,elementary ,nitrogen10 ,ann4 ,mo4 ,bot4 ,gard41 #aiad1 i41 ,no4 #b4 #eb ,wann1 ,f4 ,b41 8,the ,fixation of ,nitrogen by ,green ,plants10 ,amer4 ,journ4 ,bot41 #aiba1 viii41 pp4 #a-bi4 ,,chapter ,,vii4 ,,the ,,occurrence ,,of ,,fungi ,,in ,,the ,,soil4 ,,note4--,i am indebted to my late colleague ,miss ,sibyl ,s4 ,jewson1 ,m4,sc41 for permission to include unpublished data from our investigations on the soil fungi4 ,in #ahhf ,adametz1#a investigating the biochemical changes occurring in soils1 isolated several species of fungi4 ,it was1 however1 only with the work of ,oudemans and ,koning1#ag in #aijb when forty-five species were isolated and described1 the majority as new to science1 that the real study of the fungus flora of the soil commenced4 ,there is now no doubt that fungi form a large and very important section of the permanent soil population1 and certain forms are found only in the soil4 ,indeed1 ,takahashi#bb has reversed the earlier ideas by suggesting that fungus spores in the air are derived from soil forms4 ,the majority of investigations on this subject fall1 perhaps1 into one or more of three classes3 7a7 purely systematic studies such as those of ,oudemans and ,koning1#ag ,dale1#e ,jensen1#i ,waksman1#be;a ,hagem1#h;c ,lendner1#ab and others1 which consist in the isolation and identification of species from various soils3 7b7 physiological researches1 such as those of ,hagem#h;c on the ,mucorine of ,norway1 or the many investigations on the biochemical changes in soils produced by fungi1 such as those of ,muntz and ,coudon1#ae ,mc,lean and ,wilson1#ae ,kopeloff1#aa ,goddard1#g ,mc,beth and ,scales1#ad and others3 7c7 quantitative studies1 such as those of ,remy1#bj ,fischer1#f ,ramann1#ah ,waksman1#be;c and ,takahashi1#bb which involve numerical estimates of the fungus flora in soils4 ,,qualitative ,,study4 ,with very rare exceptions soil fungi cannot be examined in situ1 and the necessary basis of any qualitative research is the isolation of the organisms in pure culture4 ,most soil forms belong to the ,fungi imperfecti1 and often show considerable plasticity on artificial media4 ,this makes it very difficult to determine them by comparison with type herbarium specimens or published morphological diagnoses4 ,in consequence many soil fungi have not infrequently been given new specific names1 as humicola1 terricola1 and so forth1 which is very unsatisfactory1 and means that the determinations have little significance4 ,furthermore1 most artificial media are slight variations on a few common and simple themes1 and are very selective1 permitting the growth of a moiety only of the fungi present4 ,in addition1 many fungi grow so slowly that they are overwhelmed by the more rapidly germinating or spreading forms1 or on the other hand1 they may be eliminated by the metabolic products of different adjacent colonies4 ,the extremely selective nature of the technique commonly used is shown if one tabulates systematically all the fungi which have been recorded or described in soil investigations4 ,of ,phycomycetes there are fifty-six species of eleven genera2 of ,ascomycetes twelve species of eight genera2 and of ,fungi imperfecti1 including ,actinomycetes but not sterile ,mycelia1 #aig species of sixty-two genera4 ,rusts and ,smuts one might not expect1 but that of the multitudes of ,basidiomycetes growing in wood and meadow not one should have been recorded is indeed startling4 ,it was at first thought that many imperfect fungi might be conidial stages of ,basidiomycetes1 but much search among forms isolated at ,rothamsted has1 up to the present1 failed to reveal clamp connections in the hyph4 ,since various species of soil fungi have different optimum temperature1 humidity and other conditions#c one would not expect to find an even geographic distribution4 ,very little is yet known of this aspect1 but ,rhizopus nigricans1 ,mucor racemosus1 ,zygorrhynchus vuilleminii1 ,aspergillus niger1 ,trichoderma koningi1 ,cladosporium herbarum1 and many species of ,aspergillus1 ,penicillium1 ,fusarium1 ,alternaria1 and ,cephalosporium have been commonly found throughout ,north ,america and ,europe wherever soils have been examined4 ,species of ,aspergillus1 however1 would appear to be more common in the soils of south temperate regions and species of ,penicillium1 ,mucor1 ,trichoderma1 and ,fusarium more abundant in northern soils4 ,it is well known that in many plant and animal communities there occurs a definite rhythm1 various species following each other in a regular sequence as dominants in the population4 ,although it is not yet possible to make any definite statement there would seem indications that this may also be true of the soil fungi4 ,much work has been done on the distribution of species at different depths in the soil1 but the results are still confusing4 ,thus1 examining eighteen species1 ,goddard#g found no difference in relative distribution down to #e inches4 ,werkenthin#bf found identical species from #a-d inches1 and then an absence of fungi from #e-g inches1 which latter was the greatest depth he examined4 ,waksman#be found little difference in the first six inches1 but very few species below #h inches except ,zygorrhynchus vuilleminii1 which extended down to #cj inches and was often the only species occurring below #ab inches4 ,taylor#bc has reported species of ,fusarium at practically every depth to #bd inches4 ,rathbun#ai found ,aspergillus niger1 ,rhizopus nigricans1 and species of ,fusarium and ,mucor down to #cd inches1 and ,oospora lactis1 ,trichoderma koningi1 ,zygorrhynchus vuilleminii and species of ,penicillium1 ,spicaria and ,saccharomyces as deep as #dd inches4 ,eleven species were isolated from the alimentary canal of grubs and worms1 and ,rathbun concluded that soil fungi may be spread by these organisms4 ,on an unmanured grass plot at ,rothamsted twenty species were isolated from a depth of #a inch1 nineteen from #f inches1 and eleven from #ab inches1 whereas on the unmanured plot of ,broadbalk wheat field twenty-six species were obtained from #a inch1 seven from #f inches1 and five from #ab inches4 ,there appeared to be no conspicuous differences between the floras of the two plots save that in the ,broadbalk plot there were fewer ,mucorales1 and ,zygorrhynchus mlleri and ,absidia cylindrospora were absent4 ,in the grass plot samples about one-half the forms occurring at the lower levels were isolated also from the upper levels1 but in the ,broadbalk sample the five forms isolated from #ab inches1 and five out of seven of those at #f inches occurred only at those levels1 i4e4 each of the three levels appeared to have a specific flora4 ,the difference in depth distribution in these two cases may be due to the fact that in the ,broadbalk plot the stiff clay subsoil occurs at #e-g inches1 whereas in the grass plot the depth of soil is greater than #ab inches4 ,much further work needs to be done on this aspect before any definite conclusion can be reached4 ,much scattered information is available concerning the effect of soil type1 manuring1 treatment1 cropping1 and so forth upon the fungus content1 but no clear issue as yet emerges from the results4 ,hagem#h found that cultivated soils vary greatly from forest soils in the species of ,mucor present1 and that certain species seem to be associated in similar environments4 ,thus in pinewoods ,mucor ramannianus is usually found1 together with ,m4 strictus1 ,m4 flavus1 and ,m4 sylvaticus1 and with this 8,m4 ,ramannianus ,society10 ,m4 racemosus1 ,m4 hiemalis1 and ,absidia orchidis1 are frequently associated4 ,the differences found by ,hagem between the species of ,mucor from forest and cultivated land could not1 however1 be confirmed by ,werkenthin4#bf ,dale1#e examining sandy1 chalky1 peaty and black earth soils1 found specific differences1 although many of the species were common to all4 ,a soil which had been manured continuously for thirty-eight years with ammonium sulphate alone1 contained twenty-two species1 whereas the same soil with the addition of lime only had thirteen species4 ,both ,goddard#g and ,werkenthin1#bf in their investigations1 found a constant and characteristic fungus flora regardless of soil type1 tillage1 or manuring4 ,waksman's#be studies of forest soils showed few species of ,mucor but many of ,penicillium and ,trichoderma#b2 orchard soil contained no species of ,trichoderma1 very few of ,penicillium1 but a large number of species of ,mucor2 species of ,trichoderma were common in acid soils1 whilst cultivated garden soil contained all forms4 ,the examination of very differently manured plots on the ,broadbalk wheat field at ,rothamsted has not shown any striking differences in the fungus flora1 all the more important groups of species being represented in every plot1 but significant minor differences are present4 ,thus1 plot #ac1 manured with double ammonium salts1 superphosphate and sulphate of potash1 is especially rich in 8species0 of ,trichoderma1 whereas the unmanured plot contains large numbers of species of green ,penicillium1 ,trichoderma1 and a species of ,botrytis 7pyramidalis874 ,the effect of the crop upon the fungus flora is seen in cases where the same crop is grown year after year as in certain flax areas1 where species of ,fusarium accumulate in the soil and tend to produce 8flax sickness40#ac ,,quantitative ,,study4 ,as it is not possible to count the soil fungi in situ1 any estimation of the numbers present in a soil must be arrived at by indirect means4 ,the method adopted is to make as fine a suspension as possible of a known quantity of soil sample in a known amount of water1 dilute this to #a_/ejjj1 #a_/ajjjj1 and so forth by regular gradations1 incubate cubic centimetres of the final dilution on artificial media in petri dishes1 and count the colonies of fungi developing in each plate4 ,using the average figures from a series of duplicate plates1 the number of 8individual0 fungi in a gram of the original soil sample may then be calculated4 ,the very few students who have made quantitative estimations have obtained very unsatisfactory results4 ,in bacterial or protozoal estimations1 the shaking of the soil suspension separates the unicellular individuals1 so that in the final platings each individual from the soil theoretically gives rise to one colony on the medium4 ,in the case of fungi1 the organisms may be in the form of unicellular or multicellular spores or larger or smaller masses of unicellular or multicellular mycelium differing for each particular species or phase of development within the single species4 ,the organisms may be sterile in the soil or form fruiting bodies1 consisting of few or myriads of locally or widely distributed spores4 ,in the process of shaking the soil-suspension fungi of different organisation or of differing developmental stages may be broken up and moieties fragmented in totally different ways or to very different degrees4 ,with protozoa and bacteria the relation of soil individual to plate colony is direct2 with fungi we do not know what is the soil 8individual0 nor whether it is the same for different fungi2 nor can we yet profitably discuss any significant numerical relationship of plate colonies to soil organisms4 ,thus ,conn#d has pointed out that the plate count of a fungus indicates only the ability to produce reproductive bodies and found that the spores of one colony of ,aspergillus1 if distributed evenly through a kilogram of soil1 could produce the average plate counts obtained by ,waksman4 ,abundant vegetative growth may1 in some species1 reduce or inhibit spore formation1 so that of two species the one giving a lower count might really be much the more important and plentiful in the soil4 ,further1 the colonies developing in the final plates represent only a selected few of the fungi present in the soil sample1 the ,basidiomycetes1 and no doubt many other forms1 being absent4 ,in addition1 different media differ among themselves in the average number of colonies developing on the plates1 each medium giving1 as it were1 its own point of view4 ,thus1 in one experiment carried out at ,rothamsted by ,miss ,jewson1 using the same soil suspension1 twenty plates of ,coon's ,agar gave #ceg colonies1 of ,cook's ,agar #bdf1 of ,czapek's ,agar #bae1 and of ,prune ,agar #cff4 ,thus if one only used ,coon's ,agar and ,prune ,agar one would obtain a total of #gbc colonies1 whereas the same suspension on ,cook's ,agar and ,czapek's ,agar would give only #dfa1 and the calculated numbers of fungi per gram of soil would be totally different4 ,further1 if a single medium be taken1 it is found that slight alterations in the degree of acidity may make very considerable differences in the final numbers4 ,thus ,coon's ,agar acidified to a hydrogen ion concentration of #ej gave as the results of four series the following average numbers of colonies per plate1 #ag1 #bcge1 #ah1 #bc4 ,when1 however1 the medium was acidified to a ,,ph of #dj to #dc1 corresponding averages from three series were #ch1 #dfc1 and #ddh2 i4e4 the final estimations of numbers of fungi in the soil was about twice as great4 ,again1 the degree of dilution of soil suspension used in plating may also be a very serious factor4 ,thus1 if a series of dilutions be made of #a_/hj1jjj1 #a_/dj1jjj1 #a_/bj1jjj1 #a_/aj1jjj1 #a_/e1jjj and #a_/b1ejj1 the average plate numbers should be in the proportions of #a1 #b1 #d1 #h1 #af1 and #cb respectively4 ,in an actual experiment1 the following average plate numbers were obtained1 #aed1 #cbh1 #eia1 #ajdj1 #aej1 #bbde1 which show a very decided reduction in the higher numbers4 ,if1 however1 dilutions of a suspension of spores of a single species be made1 this reduction does not occur4 ,these are but three of the very numerous factors involved in the technique of quantitative estimation1 and every single factor may be the source of errors of similar magnitude1 minute fluctuations in the operations leading to the final platings having very considerable effect upon the numbers of colonies that develop4 ,by critically evaluating each particular factor in the method1 and making statistical correction1 it has1 however1 been found possible to obtain series of duplicate plates comparing very favourably and thus to extract certain figures which1 whilst not possessing any final value1 have yet a certain general and comparative worth4 ,thus1 #bjj1 #ahb1 and #afh were obtained as the averages of six plates each1 of a soil suspension divided into three parts1 and the individual plate numbers in all three series were within the range of normal distribution4 ,the meaning of these numerical estimates in relation to fungi per gram of soil sample is1 however1 entirely hypothetical1 and to have value quantitative comparison should only be made between single species or groups of species closely related physiologically1 and where the technique is standardised4 ,illustration3 ,,fig4 #ai4--,monthly ,counts of ,numbers of ,fungi per gramme of ,dry ,soil4 ,broadbalk ,plot #b 7,farmyard ,manure71 ,rothamsted4 ,x-axis3 ,apr4 #aiba ,may ,jun4 ,jul4 ,aug4 ,sep4 ,oct4 ,nov4 ,dec4 ,jan4 #aibb ,feb4 ,mar4 ,apr4 ,may ,jun4 ,jul4 ,aug4 ,sep4 ,oct4 ,y-axis3 #aj4jjj per ,gramme of ,soil ,no comparative estimations have been made of the number of fungi in the soils of different regions4 ,there are1 however1 certain figures which show that decided seasonal differences exist4 ,thus1 correcting and averaging certain of ,waksman's results#be the following numbers of fungi per gram of soil at #d inches deep are obtained2 ,september1 #gfh1jjj2 ,october1 #ebb1jjj2 ,november1 #caj1jjj2 ,january1 #ahb1jjj4 ,at ,rothamsted results have been obtained which would appear to mark a clear seasonal rhythm1 corresponding in the time of its maxima in ,autumn and ,spring with the periodicities known for many other ecological communities 7,fig4 #ai74 ,the numbers of fungi at various depths in the soil show very clearly marked differences4 ,the distribution in the top #d-f inches depending probably upon the depth of soil1 is more or less equal1 but there is a very rapid falling off in numbers1 especially between #e-i inches1 until at #bj-cj inches fungi are either very few in number or absent4 ,thus ,takahashi#bb found #eij1jjj fungi per gram at a depth of #b cms4 and only #afj1jjj at #h cms4 ,,table ,,xiii4--,,influence ,,of ,,soil ,,treatment ,,upon ,,the ,,numbers ,,of ,,fungi ,,as ,,determined ,,by ,,the ,,plate ,,method--7,,after ,,waksman74 ---------------------------------------- ------------ ,numbers of ,fungi ,soil ,fertilisation4 ,reaction4per ,gram of ,soil4 ---------------------------------------- ------------ ,p4,h4 ,minerals only #ef #cg1cjj ,heavily manured #eh #gc1jjj ,sodium nitrate #eh #df1jjj ,ammonium sulphate #dj #aaj1jjj ,minerals and lime #ff #bf1bjj ,ammonium sulphate and lime #fb #ci1ajj ---------------------------------------- ------------ ,the type of soil and its treatment exercise a great influence over the number of fungi present4 ,fischer#f found that farmyard manure increased the number of fungi in uncultivated 8,hochmoor10 cultivated 8,grunlandmoor10 and a clay soil by two1 three1 and five times respectively4 ,waksman's results#be indicate that the more fertile soils contain more fungi1 both in number and species1 than the less fertile ones1 and if one averages his results1 the following figures are obtained3 garden soil1 #ebe1jjj per gram2 orchard soil1 #bej1jjj2 meadow soil1 #gej1jjj2 and forest soil1 #aea1jjj4 ,recently ,waksman#be;e has found that manure and acid fertilisers increase the numbers of fungi in the soil1 whereas the addition of lime decreases them 7,table ,,xiii474 ,jones and ,murdock#aj examined surface and sub-surface samples of forty-six soils representing seventeen soil types in eastern ,ontario4 ,molds were fairly uniform in numbers in all soils except a sandy clay loam and sandy clay shale1 in which they were absent4 ,it has also frequently been pointed out that acid and water-logged soils are richer in fungus content than normal agricultural soils4 ,on the other hand1 ,brown and ,halversen#b found1 examining six plots receiving different treatment and studied through a complete year1 that the numbers of fungi were unaffected by moisture1 temperature1 or soil treatment4 ,against this1 however1 must be set the work of ,coleman#c who studied the activities of fungi in sterile soils and found such factors as temperature1 aeration and food supply to exercise a deciding control4 ,investigations at ,rothamsted show that ,broadbalk plot #ac1 receiving double ammonium salts1 superphosphate and sulphate of potash and yielding #ca bushels per acre1 and plot #b1 receiving farmyard manure and yielding #ceb bushels1 contain approximately equal numbers of fungi4 ,this figure is about half as high again as that for plot #c1 which is unmanured and yields #abf bushels1 plot #aj1 with double ammonium salts alone and yielding #bj bushels1 and plot #aa1 with double ammonium salts and superphosphate and yielding #bbi bushels per acre4 ,a primary factor1 however1 in all considerations such as these is the equality of distribution of fungi laterally in any particular soil4 ,there are probably few soils so homogeneous as the ,broadbalk plots at ,rothamsted1 and on plot #b 7farmyard manure since #aheb7 samples taken from the lower and upper ends and the middle region gave average numbers of colonies per plate of #bd1 #bc1 and #be respectively4 ,on the other hand1 soil samples taken only a few yards apart in the middle region of the plot gave average plate counts of #ccg and #efh4 ,,conclusion4 ,surveying generally the field covered in this chapter1 one can only be impressed with the fragmentary character of our knowledge and with the fact that1 owing to the selective nature of the technique1 the data we possess1 if assumed to be representative1 give an entirely partial and erroneous picture of the soil fungi4 ,from the qualitative aspect1 the chief impediment is the impossibility of obtaining reliable specific determinations of very many of the soil fungi4 ,lists of doubtfully-named forms from particular soils or geographic regions are useless or a positive evil1 and there is imperative need for the systematising of selected genera by physiological criteria1 such as has been partially done for ,penicillium1 ,fusarium1 and ,aspergillus4 ,furthermore1 until a standardised and non-selective technique has been devised1 or a number of standardised selective methods for particular groups1 comparative investigations into specific distribution can give little of value4 ,this latter criticism is also very applicable if regard be paid to the quantitative aspect of soil work1 for progress here largely depends upon the elaboration of a standardised fractionation technique4 ,every single factor in these methods needs exact analysis1 for each gives opportunity for great error1 and each error is magnified many thousand times in the final results4 ,much has been done in this direction at ,rothamsted1 but more remains to do4 ,finally1 working with single species in sterilised soil under standardised conditions1 there is fundamental work to be done on the relation of plate colony to soil 8individual40 #a ,adametz1 ,i41 8,untersuchungen ber die niederen ,pilze der ,ackerkrume10 ,inaug4 ,diss41 ,leipzig1 #ahhf4 #b ,brown1 ,p4 ,e41 and ,halversen1 ,w4 ,v41 8,effect of ,seasonal ,conditions and ,soil ,treatment on ,bacteria and ,molds in ,soil10 ,iowa ,agric4 ,expt4 ,sta4 #aiba1 ,res4 ,bull41 #ef4 #c ,coleman1 ,d4 ,a41 8,environmental ,factors ,influencing the ,activity of ,soil ,fungi10 ,soil ,sci41 #aiaf1 v41 #b4 #d ,conn1 ,h4 ,j41 8,the ,microscopic ,study of ,bacteria and ,fungi in ,soil10 ,n4,y4 ,agric4 ,expt4 ,sta41 #aiah1 ,bull4 #fd4 #e ,dale1 ,e41 7a7 8,on the ,fungi of the ,soil10 ,ann4 ,mycol41 #aiab1 #aj2 7b7 8,on the ,fungi of the ,soil10 ,ann4 ,mycol41 #aiad1 #ab4 #f ,fischer1 ,h41 8,bakteriologisch-chemische ,untersuchungen2 ,bakteriologischen ,teil10 ,landw4 ,jahrb41 #aiji1 #ch4 #g ,goddard1 ,h4 ,m41 8,can ,fungi living in ,agricultural ,soil ,assimilate ,free ,nitrogen80 ,bot4 ,gaz41 #aiac1 #ef4 #h ,hagem1 ,o41 7a7 8,untersuchungen ber ,norwegische ,mucorineen ,i41 ,vidensk4 ,selsk1 ,i410 ,math4 ,naturw4 ,klasse1 #aijg1 #g2 7b7 8,untersuchungen ber ,norwegische ,mucorineen ,,ii41 ,vidensk4 ,selsk4 ,i410 ,math4 ,naturw4 ,klasse1 #aiaj1 #aj4 #i ,jensen1 ,c4 ,n41 8,fungus ,flora of the ,soil10 ,n4,y4 7,cornell7 ,agric4 ,expt4 ,sta41 #aiab1 ,bull4 #cae4 #aj ,jones1 ,d4 ,h41 and ,murdock1 ,f4 ,g41 8,quantitative and ,qualitative ,bacterial ,analysis of ,soil ,samples taken in ,fall of #aiah10 ,soil ,sci41 #aiai1 #h4 #aa ,kopeloff1 ,n41 8,the ,effect of ,soil ,reaction on ,ammonification by ,certain ,soil ,fungi10 ,soil ,sci41 #aiaf1 #a4 #ab ,lendner1 ,a41 8,les ,mucorines de la ,suisse10 #aijh4 #ac ,manns1 ,s4 ,f41 8,fungi of ,flax-sick ,soil and ,flax ,seed10 ,thesis1 ,n4 ,dak4 ,agric4 ,expt4 ,sta41 #aijc4 #ad ,mc,beth1 ,i4 ,g41 and ,scales1 ,f4 ,m41 8,the ,destruction of ,cellulose by ,bacteria and ,filamentous ,fungi10 ,u4,s4 ,dept4 ,agric4 ,bur4 ,plant ,indust41 #aiac1 ,bull4 #bff4 #ae ,mc,lean1 ,h4 ,c41 and ,wilson1 ,g4 ,w41 8,ammonification ,studies with ,soil ,fungi10 ,n4,j4 ,agric4 ,expt4 ,sta41 #aiad1 ,bull4 #bgj4 #af ,muntz1 ,a41 and ,coudon1 ,h41 8,la fermentation ammoniaque de la terre10 ,compt4 ,rend4 ,acad4 ,sci4 7,paris71 #ahic1 #aaf4 #ag ,oudemans1 ,a4 ,c41 and ,koning1 ,c4,j41 8,prodrome d'une flore mycologique1 obtenue par la culture sur gelatin prpare de la terre humeuse du ,spanderswoud1 prs de ,bussum10 ,arch4 ,nerland4 ,sci4 ,exact et ,nat41 #aijb1 s4 ii41 #g4 #ah ,ramann1 ,e41 8,bodenkunde10 ,berlin1 #aije4 #ai ,rathbun1 ,a4 ,e41 8,the ,fungus ,flora of ,pine ,seed ,beds10 ,phytopath41 #aiah1 #h4 #bj ,remy1 ,t41 8,bodenbakteriologischen ,studien10 ,centr4 f4 ,bakt41 #aijb1 ii41 #h4 #ba ,sherbakoff1 ,c4 ,d41 8,fusaria of ,potatoes10 ,n4,y4 7,cornell7 ,agric4 ,expt4 ,sta41 #aiae1 ,mem4 #f4 #bb ,takahashi1 ,t41 8,on the ,fungus ,flora of the ,soil10 ,anns4 ,phytopath4 ,soc41 ,japan1 #aiai1 #a4 #bc ,taylor1 ,m4 ,w41 8,the ,vertical ,distribution of ,fusarium10 ,phytopath41 #aiag1 #g4 #bd ,thom1 ,ch41 8,cultural ,studies of ,species of ,penicillium10 ,u4,s4 ,dept4 ,agric4 ,bur4 ,animal ,indus41 #aiaj1 ,bull4 #aah4 #be ,waksman1 ,s4 ,a41 7a7 8,soil ,fungi and their ,activities10 ,soil ,sci41 #aiaf1 #b2 7b7 8,do ,fungi ,actually ,live in the ,soil and ,produce ,mycelium80 ,science1 #aiaf1 #dd2 7c7 8,is there any ,fungus ,flora of the ,soil80 ,soil ,sci41 #aiag1 #c2 7d7 8,the ,importance of ,mold ,action in the ,soil10 ,soil ,sci41 #aiah1 #f2 7e7 8,the ,growth of ,fungi in the ,soil10 ,soil ,sci41 #aibb1 xiv4 #bf ,werkenthin1 ,f4 ,c41 8,fungus ,flora of ,texas ,soils10 ,phytopath41 #aiaf1 #f4 ,,chapter ,,viii4 ,,the ,,life ,,of ,,fungi ,,in ,,the ,,soil4 ,in the last chapter fungi were considered as so many specific but functionless units in the soil4 ,unless1 however1 they are regarded merely as inert spore contaminations from the air1 a view which is now no longer tenable1 their very presence implies the existence of innumerable vital relationships between the organisms and their environment4 ,from this point of view the studies treated in the previous chapter are but the necessary first steps to an understanding of the relation of soil fungi to living plants and of the part played by them in the soil economy4 ,,relation ,,of ,,soil ,,fungi ,,to ,,living ,,plants4 ,older classifications of fungi frequently divided these organisms into four categories--parasites1 saprophytes1 facultative parasites1 and facultative saprophytes1 but the further mycological studies are carried the more clearly it is seen that these groups are entirely artificial4 ,there are probably few fungi that cannot1 under particular conditions1 invade living tissues1 and it only seems a question of time before at all events the vast majority of fungi will be grown on synthetic media in the laboratory4 ,from our present point of view the importance of this lies in the fact that fungi living saprophytically in the soil may1 given the right conditions or the presence of some particular host plant1 become parasites or symbionts1 and conversely well-known pathogens may live a saprophytic existence4 ,thus ,cucumber ,leaf ,spot is caused by ,colletotrichum oligochtum1 and ,bewley#c has repeatedly isolated this fungus from glasshouse manure and refuse of various kinds4 ,in his early studies1 ,butler#ac isolated many parasitic species of ,pythium from ,indian soils1 and the presence of ,p4 de ,baryanum as a soil saprophyte has been confirmed by ,bussey1 ,peters1 and ,ulrich4#aa ,de ,bruyn#ag has recently found that most species of ,phytophthora1 including ,p4 erythroseptica and ,p4 infestans may live as saprophytes in the soil1 whilst ,pratt#ec has isolated from virgin lands and desert soils various fungi1 which cause disease in potatoes4 ,in #aiab ,jensen#bi gave a list of twenty-three 8facultative parasites0 isolated from soil1 and these are but a moiety of those which could be listed to-day4 ,furthermore1 it was shown by ,frank#bd many decades ago that forest humus is not merely a mass of the remains of animals and plants1 but that a considerable part of its organic substance is made up of fungus hyph1 which ramify and penetrate in all directions4 ,evidence is rapidly accumulating that this is also true of most other soils containing organic matter4 ,it is well known that many of the higher plants live in symbiotic or commensal relationship with these humus fungi1 which are present in the host tissues as mycorrhiza1 and further studies only serve to show the widespread and fundamental nature of this relationship4 ,thus many ,basidiomycetes#ej 7species of ,tricholoma1 ,russula1 ,cortinarius1 ,boletus1 ,elaphomyces1 etc47 possess a mycorrhizal relationship with various broad leaved trees1 such as beech1 hazel1 and birch#eg and with various conifers and certain ,ericales4 ,other ,ericales show this relationship with species of the genus ,phoma1#fb many orchids1 with species of ,rhizoctonia#b 7or ,orcheomyces#aj71 whilst ,gastrodia elata contains ,armillaria mellea4#cf ,certain species of ,pteridophyta and ,bryophyta are also known to certain mycorrhizal fungi4 ,of the numerous fungi taking part in these mycorrhizal relationships1 only a small number have yet been identified1 but there is little doubt that perhaps the majority of these organisms must be regarded as true soil forms4#ad1de ,the mycological flora of the soil thus plays an important part in the life of many higher forms of vegetation1 and this relationship is a very fruitful field for study4 ,,relation ,,of ,,fungi ,,to ,,soil ,,processes4 ,the great cycle of changes occurring in the soil whereby organic matter is gradually transformed and again made available as plant food is entirely dependent upon micro-organisms4 ,until a decade ago it was thought that bacteria were by far the most important group concerned in the bringing about of these changes1 but recent studies have shown that1 in at all events certain arcs of this great organic cycle1 the fungi have1 perhaps1 an equal part to play4 ,the life of fungi in the soil may1 for our purposes1 be considered from three points of view--their part in the decomposition of carbon compounds1 their nitrogen relationships1 and their work in the mineral transformations of the soil4 ,,carbon ,,relationships4 ,of primary importance in the carbon relationships of soil fungi is the part played in the decomposition of the celluloses1 which compose almost all the structural remains of plant tissues4 ,our first real knowledge of this subject was given by ,van ,iterson#bh in #aijd when he showed the wide extent of cellulose destruction by fungi1 and devised methods whereby fifteen cellulose-decomposing forms1 many of which have since proved to be common soil fungi1 were isolated4 ,three years later ,appel#a published his account of the genus ,fusarium1 and showed that many of the species could destroy filter paper4 ,a difficulty was introduced in #aijh by ,schellenberg1#fj who1 working with common soil forms1 found that only hemicelluloses and not pure cellulose were destroyed4 ,this has recently been supported by ,otto1#dh but from the practical point of view the discussion is academic for the amount of pure cellulose in plants is insignificant4 ,in #aiac ,mc,beth and ,scales#dc showed that a considerable number of common soil fungi were most active cellulose destroyers1 pure precipitated cellulose and cotton being readily attacked4 ,this was supported by ,mc,beth in #aiaf1db whilst ,scales#ei has found that most species of ,penicillium and ,aspergillus decompose cellulose1 especially where ammonium sulphate is the source of nitrogen4 ,waksman#fe tested twenty-two soil fungi and found that eleven decomposed cellulose rapidly and four slowly1 whilst ,dascewska1#af ,waksman1#ff1fg and others have concluded that soil fungi play a more important part in the decomposition of cellulose and in 8humification0 than soil bacteria4 ,schmitz#fa has recently shown that cellulose-destroying bacteria play no important part in the decay of wood under natural conditions4 ,in addition to the celluloses1 practically all simple and complex organic carbon compounds are attacked by soil fungi1 and in many cases the decomposition is very rapid4#bf ,many ,actinomycetes1 ,aspergilli and ,penicillia are active starch splitters1 and it is of interest to note that some of the strongest cellulose decomposers 7,melanconium sp41 ,trichoderma sp41 and ,fusaria7 secrete little diastase4#ff ,the ,mucorales apparently do not attack cellulose1 but can only utilise pectin bodies1 monosaccharides1 and partly disaccharides4#bf ,dox and ,neidig#ai have shown that various species of ,aspergillus and ,penicillium are able to attack the soil pentosans4 ,roussy1#eh ,kohshi1#bd ,verkade and ,shngen1#fd and many other workers have found that fats and fatty acids are readily used as food by soil fungi1 and ,koch and ,oelsner#cc have recently shown that tannins are readily assimilated4 ,klcker1#cb ,ritter1#ef and others have shown that the utilisation of many carbon compounds is to a large extent determined by the source of nitrogen and its concentration in the pabulum4 ,there would seem1 therefore1 no doubt that the decomposition of celluloses and other carbon compounds is of primary importance in the life-activities of soil fungi4 ,,nitrogen ,,relationships4 ,in this section we shall consider the problems of nitrogen fixation and nitrification1 of ammonification1 and of the utilisation of nitrogenous compounds by soil fungi4 ,as soil fungi form so large a part of the soil population1 the question of whether they can make use of the free nitrogen of the air is of primary importance4 ,during the last two decades many investigators have attempted to solve the problem1 often studying allied or identical species2 but if one consults some thirty researches published during this period1 opinion is found to be about equally divided4 ,even1 however1 in those studies where nitrogen fixation has been recorded the amounts are very slight1 usually being below #e mgrms4 per #ej c4c4 of solution1 and often being obviously within the limits of experimental error4 ,latham1#cg however1 working on ,aspergillus niger1 recorded variations ranging from a nitrogen loss of #dbe mgrms4 to a nitrogen fixation of #bjea mgrms4 per #ej c4c4 of medium4 ,ternetz#fc found that different strains of ,phoma radicis may fix from #be mgrms4 of nitrogen in the lowest case1 to #aeg mgrms4 in the highest per #ej c4c4 of nutrient solution4 ,duggar and ,davis#bj report that ,phoma bet may fix nitrogen in quantities of #gge mgrms4 per #ej c4c4 of medium4 ,the latter authors1 in a very able critique of the problem1 indicate certain possible sources of error in previous work1 and if one examines the studies in which nitrogen fixation has been recorded in the light of these criticisms1 it is difficult not to think that1 with the exception of the genus ,phoma1 good evidence for nitrogen fixation by fungi is lacking4 ,phoma bet is a common pathogen attacking beets1 whilst ,p4 radicis is a mycorrhizal form inhabiting various ,ericales4 ,apart from these exact quantitative studies1 which have given a negative verdict1 there is a considerable amount of positive but indirect evidence for nitrogen fixation by mycorrhizal fungi1#ee and it is very unfortunate that more of these forms have not been investigated quantitatively4 ,as the evidence stands to-day1 one must conclude that the fungus flora does not play any part in the direct nitrogen enrichment of the soil4 ,equally obscure is the question of nitrification and denitrification by soil fungi1 but this is the result of a lack of study rather than of a plethora of indeterminate researches4 ,direct nitrification or denitrification has not been established1 but the work of ,laurent#ch and a few other workers appears to show that soil fungi can reduce nitrates to nitrites4 ,the second primary nitrogen relationship that we have to consider is the process of ammonification4 ,the ammonifying power of soil fungi was first demonstrated by ,muntz and ,coudon1#df and by ,marchal#dj in #ahic1 the former showing that ,mucor racemosus and ,fusarium ,muntzii gave a larger accumulation of ammonia in soil than any of the bacteria tested2 and the latter that ,aspergillus terricola1 ,cephalothecium roseum and other soil fungi were active ammonifiers1 especially in acid soils4 ,shibata1#fb ,perotti1#di ,hagem1#bf ,kappen1#ca ,lhnis1#ci and others1 have observed that urea1 dicyanamide and cyanamide are decomposed with the liberation of ammonia2 and ,hagem#bf has recorded the same process for peptones1 amino acids1 and other organic nitrogen compounds in plant and animal remains in the soil4 ,the latter author considers soil fungi more important ammonifying agents in the soil than bacteria1 a conclusion in which ,mc,lean and ,wilson1#dd and perhaps most later workers concur4 ,mc,lean and ,wilson#dd found large differences in the ammonifying powers of various soil fungi1 the ,moniliace being the strongest ammonifiers1 the ,aspergillace the weakest4 ,generic and specific differences have been confirmed by ,coleman1#ae ,waksman1#fg and other authors4 ,waksman and ,cook#gj suggested that such variations may be due1 not to innate differences in the metabolic activities of the several organisms1 but to differences in reproductive times1 and that there might be some relationship between sporogeny and the ability to accumulate nitrogen4 ,kopeloff#ce has carried out experiments on the inoculation of sterilised soil with known quantities of spores and found that1 although the amount of ammonia accumulated increased with the number of spores the proportion was not direct but modified by the food supply4 ,after the first five days' growth1 the rate of ammonia production varied markedly in a two-day rhythm which seemed to be due to the metabolism of the fungus rather than to recurrent stages of spore formation and germination in the life history4 ,the amount of ammonia liberated has been shown by recent work#ff to depend upon the available sources of carbon and nitrogen4 ,in the absence of a carbohydrate supply the protein is attacked both for carbon and nitrogen1 and since more of the former is required much ammonia is liberated4 ,in addition1 however1 to the carbon and nitrogen control1 the process of ammonification by soil fungi is intimately related to physical conditions4 ,working with pure cultures1 ,mc,lean and ,wilson1#dd ,coleman1#ae ,kopeloff1#ce ,waksman and ,cook1#gj and other students1 have shown that the amount of ammonia accumulated depends upon such factors as the presence of phosphates1 the period of incubation of the fungi1 aeration1 the moisture in the soil1 the temperature1 the degree of soil acidity1 the type of soil1 and so forth4 ,that fungi take a very important place as ammonifying agents in the soil can no longer be doubted1 but the question yet remains to be considered of the balance of profit or loss resulting from their activities4 ,it has usually been considered that a part of the ammonia freed is used by the fungi themselves1 but that the greater part is liberated1 and so rendered available to nitrifying organisms4 ,both ,neller#dg and ,potter and ,snyder#ea found that typical soil fungi inoculated into sterile soil grew with a vigour approximately equal to the growth induced by an inoculation of the entire soil flora4 ,this is largely to be accounted for by the fact that when soils are sterilised by heat or by certain chemicals1 breaking-down changes occur1 and substances are liberated which are peculiarly favourable to fungus growth4 ,this fact must be borne in mind when interpreting ammonification and other studies where the method is that of inoculation of fungi into sterilised soil4 ,in many cases it tends to nullify any application of the results to normal soils1 whilst in others the conclusions must be accepted with some reserve4 ,in all cases ,potter and ,snyder#ea found that fungi caused a diminution in the amount of nitrates1 that the ammonia was not much changed in amount1 and that there was a decrease in the quantities of soluble non-protein nitrogen4 ,the range of organic and inorganic nitrogenous compounds utilisable by soil fungi is very great4 ,ritter#ef has shown that certain forms can use the nitrogen of 8free0 nitric acid in the medium2 ,ritter1#ef ,hagem1#bf and others1 that soil fungi can use ammonia nitrogen equally with nitrate nitrogen1 and ,ehrenberg#ba concluded that soil fungi play a more important part in the building of albuminoids from ammonia than bacteria do4 ,ehrlich#bb has shown that various heterocyclic nitrogen compounds and alkaloids can serve as sources of nitrogen to soil fungi1 whilst ,ehrlich and ,jacobsen#bc have found that soil fungi can form oxy-acids from amino-acids4 ,hagem1#bf ,povah1#eb ,bokorny1#f1h and others1 state that for many soil forms organic nitrogen sources are better than inorganic sources1 and that peptones1 amino-acids1 urea1 and uric acids1 etc41 are very quickly utilised by species of ,mucor1 yeasts1 and so forth4 ,butkevitch1#ab and ,dox#ah have recently found that it depends on circumstances which compounds of protein molecule can be utilised by particular fungi1 and that soil fungi can utilise both amino and amido complexes for the formation of ammonia4 ,in #aiai ,boas#d showed for ,aspergillus niger that if a number of nitrogenous compounds are available the fungus absorbs the most highly dissociated4 ,in the welter of scattered observations on the utilisation of nitrogenous compounds1 it is difficult to trace any clear issue4 ,that proteins1 amino-acids1 and other complex organic compounds are readily broken down to ammonia by soil fungi is clear1 and1 on the other hand1 it is also clear that soil fungi utilise extensively ammonia and nitrates as sources of nitrogen4 ,on which side the balance lies it is yet impossible to say4 ,,mineral ,,relationships4 ,heinze#bg and ,hagem#bf have stated that soil fungi make the insoluble calcium1 phosphorus1 and magnesium compounds in soil soluble and available for plant food2 and ,butkevitch#ab has used ,aspergillus niger in determining the availability of the mineral constituents1 but practically no work has yet been carried out on these problems4 ,a further matter on which sound evidence is greatly to be desired is the part played by soil fungi in the oxidation processes of iron and sulphur4 ,a point which may be mentioned here1 as it is of some considerable practical importance1 is the large quantity of oxalic1 citric1 and other acids formed by certain common soil fungi4 ,acid formation is partly dependent upon the species of fungus--even more the physiological race within the species--and partly upon the substratum1 particularly the source of carbon4#e1ed ,it is interesting that as a group ,actinomycetes do not form acids from the carbon source but alkaline substances from the nitrogen sources4#fi ,,control ,,of ,,soil ,,fungi4 ,in the preceding sections an attempt has been made to sketch rapidly the chief outlines of the widespread relationships of soil fungi and of the fundamental part that they play in the biochemical changes occurring in the soil4 ,it will be evident1 even from this survey1 that their occurrence is of the utmost agricultural importance1 both when helpful as in mycorrhizal relationships or as agents in making complex organic materials available as plant food1 or when harmful as when causal agents of disease in plants4 ,it is clear that could the soil fungi be controlled to human ends by the encouragement of the useful forms and the elimination of the harmful1 a valuable power would be placed in the hands of the grower of plants4 ,certain aspects of this control1 the cruder and more destructive perhaps1 are already practicable1 whilst the finer and more constructive aspects remain possibilities of to-morrow4 ,theoretically1 the technique of control is selective in that it aims to determine one or more particular fungi1 leaving the remaining flora untouched4 ,its highest expression is seen1 perhaps1 in the utilisation of pure cultures of mycorrhizal fungi for horticultural purposes1 such as orchid cultivation1 but there is no reason why this should not be done for other purposes on a field scale similar to the way in which cultures of special strains of the root nodule organisms of legumes are employed4 ,a second aspect is the direct encouragement of special components of the fungus flora for particular purposes by selective feeding4 ,thus1 in a laboratory experiment1 ,mc,beth and ,scales#dc record an increase of #bjjj times in cellulose-destroying and other soil fungi by this method4 ,it has been pointed out that soil fungus activities such as ammonification1 proteolysis and carbohydrate decomposition are controlled by factorial equilibria1 and for special purposes it would seem feasible to weight the balance so that particular activities may be favoured4 ,a further step in this direction is the controlling of particular physical conditions so that the activities of certain fungi may be restricted4 ,professor ,l4 ,r4 ,jones#cj and his colleagues at ,madison have shown the primary importance of the control of the soil temperature in certain parasitic relationships2 the work of ,gillespie and ,hurst#be and later workers has demonstrated that the parasitism of certain species and strains of ,actinomyces upon the potato is conditioned by definite ranges of soil acidity2 and many other relationships of similar nature are known4 ,data along such lines are rapidly accumulating1 and in certain cases are already susceptible of practical application4 ,in other cases1 particular soil fungi are less open to persuasive influences1 and more drastic treatment needs to be adopted4 ,certain chemicals mixed intimately with the soil increase or diminish the numbers of particular fungi or groups of fungi2 whilst these organisms may be totally eliminated from the soil by wet or dry heat for definite periods or by treatment with potent fungicides such as formaldehyde4 ,although soil sterilisation and crude treatment in other ways has been practised for decades1 the possibility of a more delicate control of soil fungi is only now being realised4 ,its concrete expression will depend upon the progress that is made in exact knowledge of the activities of soil fungi under natural and controlled conditions1 of the balance of factors in the environment which controls any particular function and of the genetic nature of the soil fungi which occur4 ,each of these aspects is a fruitful field of study4 ,,relation ,,to ,,soil ,,fertility4 ,from a general survey of the researches that have been carried out on soil fungi during the past two decades certain issues emerge4 ,it would seem clear that fungi occupy1 perhaps1 a primary place as factors in the decomposition of celluloses1 and thus may be the chief agents in the transformation of plant remains to humus and to soluble compounds which can be used as food by the nitrogen-fixing bacteria4 ,furthermore1 soil fungi are very important ammonifiers1 but whether the balance of ammonia freed is utilised by the fungi themselves1 or whether it is made available to nitrifying bacteria is not yet clear4 ,if the latter is the case1 soil fungi play a valuable indirect rle in the accumulation of available plant food in the soil4 ,on the other hand1 by utilising nitrates as sources of nitrogen1 fungi may play an important part in the depletion of the nitrogenous food in the soil available to crop plants4 ,thirdly1 soil fungi apparently take no part in the direct nitrogen enrichment of the soil4 ,thus1 soil fungi would seem to be the most important factor in the first half of that great cycle whereby organic remains become again available as organic food4 ,the impression left on one's mind by the study of the life of fungi in the soil is of an infinitely complex series of moving equilibria1 the living activities being determined by both biological and physico-chemical conditions4 ,all these factors play an integral part in the life of the soil fungi and must be considered if a true picture is to be drawn4 ,the principal factors may be classified into the following groups3 ,most evident1 perhaps1 are the natures and specificities of the fungi and the relative composition of the fungus flora4 ,equally important1 however1 are the quantity and quality of the foods available and the non-biological environment which results from the complex series of physical and chemical changes occurring in the soil causally independent of the organisms present1 which interacts with the equally vast series of changes resulting from fungus activities4 ,finally1 one must consider the interacting biological environment of surface animals and plants and the microscopic fauna and flora4 ,the complexities are such that only the application of ,baconian principles can unravel them4 ,a beginning has been made in the study of pure cultures of soil fungi on synthetic media1 and much valuable data have accrued1 but it is obviously not possible to apply directly to soil the results obtained in such work4 ,they remain possibilities2 in certain cases probabilities1 but nothing more4 ,a further step1 one already taken and of great promise1 is the investigation of the changes occurring in sterilised soils inoculated with known quantities of one or more pure cultures of particular soil fungi4 ,such intensive study of single factors in a standardised natural or artificial soil1 to which has been added a pedigreed fungus1 is1 perhaps1 the most fruitful avenue of progress4 ,in all such work1 however1 one must bear acutely in mind the fact that a sterilised soil and1 still more1 an artificial soil1 is a very different complex from a normal soil1 and that results obtained from the inoculation of such soils are not applicable directly in the elucidation of ordinary soil processes4 ,at present there is no method known of completely sterilising a soil which does not destroy the original physico-chemical balance4 ,it is evident that the complexities are such that chemist1 physicist1 and biologist must all co-operate if the significance of the processes is to be understood1 and a solid foundation laid for future progress and for practical application4 #a ,appel1 ,o41 8,untersuchungen ber die ,gattung ,fusarium10 ,mitt4 ,biol4 ,reichanst4 ,land- u4 ,forstw41 #aijg1 #d4 #b ,bernard1 ,n41 8,l'volution dans la symbiose4 ,les ,orchides et leurs ,champignons commensaux10 ,ann4 ,sci4 ,nat4 7,bot471 ,ser4 #i1 #aiji1 #i4 #c ,bewley1 ,w4 ,f41 8,anthracnose of the cucumber under glass10 ,journ4 ,min4 ,agric41 #aibb1 xxix4 #d ,boas1 ,f41 8,die ,bildung lslicher ,strke im elektiven ,stickstoff-,stoffwechsel10 ,ber4 deut4 bot4 ,ges41 #aiai1 #cg4 #e ,boas1 ,f41 und ,leberle1 ,h41 8,untersuchungen ber ,surenbildung bei ,pilzen und ,hefen ,,ii410 ,biochem4 ,ztschr41 #aiah1 #ib4 #f ,bokorny1 ,t41 8,benzene derivatives as sources of nourishment10 ,zentr4 ,physiol41 #aiag1 #cb4 #g ,bokorny1 ,t41 8,sugar fermentation and assimilation10 ,allg4 ,brau4 ,hopfen ,zeit41 #aiag1 #eg4 #h ,bokorny1 ,t41 8,verhaltung einiger organischer ,verbindungen in der lebenden ,zelle10 ,pflgers ,archiv41 #aiag1 #afh4 #i ,brown1 ,p4 ,e41 8,mould action in soils10 ,science1 #aiag1 #df4 #aj ,burgeff1 ,h41 8,die ,wurzelpilze der ,orchideen10 ,jena4 #aiji4 #aa ,bussey1 ,w41 ,peters1 ,l41 and ,ulrich1 ,p41 8,ueber das ,vorkommen von ,wurzelbranderregern im ,boden10 ,arb4 ,kais4 ,biol4 ,anst4 ,land- u4 ,forstw41 #aiaa1 #h4 #ab ,butkevitch1 ,v4 ,s41 8,ammonia as a product of protein transformations caused by mould fungi1 and the conditions of its formation10 ,recueil d'articles dedi au ,prof4 ,c4 ,timiriazeff1 #aiaf4 #ac ,butler1 ,e4 ,j41 8,an account of the genus ,pythium and some ,chytridiace10 ,mem4 ,dept4 ,agr4 ,india1 #aijg1 ,bot4 ,ser4 #e1 #a4 #ad ,christoph1 ,h41 8,untersuchungen ber die mykotrophen ,verhltnisse der ,ericales und die ,keimung von ,pirolaceen10 ,beihefte ,bot4 ,centr41 #aiba1 #bh4 #ae ,coleman1 ,d4 ,a41 8,environmental factors influencing the activity of soil fungi10 ,soil ,sci41 #aiaf1 #b4 #af ,dascewska1 ,w41 8tude sur la dsagrgation de la cellulose dans la terre de bruyre et la tourbe10 ,univ4 ,genve1 ,inst4 ,bot41 #aiac1 ,s4 #h4 #ag ,de ,bruyn1 ,h4 ,l4 ,g41 8,the saprophytic life of ,phytophthora in the soil10 ,meded4 v4 d4 ,landbouwhoogeschool ,wageningen1 #aibb1 xxiv4 #ah ,dox1 ,a4 ,w41 8,amino acids and micro-organisms10 ,proc4 ,iowa ,acad4 ,sci41 #aiag1 #bd4 #ai ,dox1 ,a4 ,w41 and ,neidig1 ,r4 ,e41 8,pentosans in lower fungi10 ,journ4 ,biol4 ,chem41 #aiaa1 #i4 #bj ,duggar1 ,b4 ,m41 and ,davis1 ,a4 ,r41 8,studies in the physiology of the fungi4 7,i47 ,nitrogen fixation10 ,ann4 ,mo4 ,bot4 ,gard41 #aiaf1 #c4 #ba ,ehrenberg1 ,p41 8,die ,bewegung des ,ammoniakstickstoffs in der ,natur10 ,mitt4 ,landw4 ,inst41 ,breslau1 #aijg1 #d4 #bb ,ehrlich1 ,f41 8,yeasts1 moulds1 and heterocyclic nitrogen compounds and alkaloids10 ,biochem4 ,ztschr41 #aiag1 #gi4 #bc ,ehrlich1 ,f41 and ,jacobsen1 ,k4 ,a41 8ber die ,umwandlung von ,aminosuren in ,oxysuren durch ,schimmelpilze10 ,ber4 ,deut4 ,chem4 ,gesell41 #aiaa1 #dd4 #bd ,frank1 ,b41 8,ueber die auf ,wurzelsymbiose beruhende ,ernhrung gewisser ,bume durch unterirdische ,pilze10 ,ber4 d4 ,deut4 ,bot4 ,gesell41 #ahhe1 #c4 #be ,gillespie1 ,l4 ,j41 and ,hurst1 ,l4 ,a41 8,hydrogen-ion concentration--soil type--common potato scab10 ,soil ,sci41 #aiah1 #f4 #bf ,hagem1 ,o41 8,untersuchungen ber ,norwegische ,mucorineen10 ,vidensk4 ,selsk4 ,i41 ,math4 ,naturw4 ,klasse1 #aiaj1 #g4 #bg ,heinze1 ,b4 ,h41 8,sind ,pilze imstande den elementaren ,stickstoff der ,luft zu verarbeiten und den ,boden an ,gesamtstickstoff anzureichen10 ,ann4 ,mycol41 #aijf1 #d4 #bh ,van ,iterson1 ,c41 8,die ,zersetzung von ,cellulose durch ,arobe ,mikroorganismen10 ,centr4 f4 ,bakt41 #aijd1 ii1 #aa4 #bi ,jensen1 ,c4 ,n41 8,fungous flora of the soil10 ,agric4 ,expt4 ,sta4 ,cornell1 ,bull4 #aiab1 #cae4 #cj ,jones1 ,l4 ,r41 8,experimental work on the relation of soil temperature to disease in plants10 ,trans4 ,wisc4 ,acad4 ,sci41 #aibb1 #bj4 #ca ,kappen1 ,h41 8,ueber die ,zersetzung des ,cyanamids durch ,pilze10 ,centr4 f4 ,bakt41 #aiaj1 ii1 #bf4 #cb ,klcker1 ,a41 8,contribution la connaissance de la facult assimilatrice de douze espces de levure vis--vis de quatre ,sucres10 ,compt4 ,rend4 ,trav4 ,lab41 ,carlsberg1 #aiai1 #ad4 #cc ,koch1 ,a41 und ,oelsner1 ,a41 8,einfluss von ,fichtenharz und ,tannin auf den ,stickstoffhaushalt des ,bodens und seiner physikalischen ,eigenschaften10 ,centr4 f4 ,bakt41 #aiaf1 ii1 #de4 #cd ,kohshi1 ,o41 8,ueber die fettzehrenden ,wirkungen der ,schimmelpilze nebst dem ,verhalten des ,organfettes gegen ,fulnis10 ,biochem4 ,ztschr41 #aiaa1 #ca4 #ce ,kopeloff1 ,n41 8,the inoculation and incubation of soil fungi10 ,soil ,sci41 #aiaf1 #a4 #cf ,kusano1 ,s41 8,gastrodia elata and its symbiotic association with ,armillaria mellea10 ,journ4 ,coll4 ,agric41 ,imp4 ,univ41 ,tokyo1 #aiaa1 iv4 #cg ,latham1 ,m4 ,e41 8,nitrogen assimilation of ,sterigmatocystis niger and the effect of chemical stimulation10 ,torrey ,bot4 ,club1 ,bull4 #aiji1 #cf4 #ch ,laurent1 8,les reduction des nitrates en nitrites par les graines et les tubercles10 ,bull4 ,acad4 ,roy4 ,sci4 ,belg41 #ahij1 #bj4 #ci ,lhnis1 ,f41 8,ammonification of cyanamid10 ,ztschr4 f4 ,grungsphysiol41 #aiad1 v4 #dj ,marchal1 ,e41 8,sur la production de l'ammoniaque dans le sol par les microbes10 ,bull4 ,acad4 ,roy4 ,sci4 ,belg41 #ahic1 #be4 #da ,maz1 ,p41 ,vila et ,lemoigne1 8,transformation de la cyanamide en ure par les microbes du sol10 ,compt4 ,rend4 ,acad4 ,sci41 ,paris1 #aiai1 #afi4 #db ,mc,beth1 ,i4 ,g41 8,studies on the decomposition of cellulose in soils10 ,soil ,sci41 #aiaf1 ,i4 #dc ,mc,beth1 ,i4 ,g41 and ,scales1 ,f4 ,m41 8,the destruction of cellulose by bacteria and filamentous fungi10 ,u4,s4 ,dept4 ,agric1 ,bur4 ,pl4 ,ind41 #aiac1 ,bull4 #bff4 #dd ,mc,lean1 ,h4 ,c1 and ,wilson1 ,g4 ,w41 8,ammonification studies with soil fungi10 ,new ,jersey ,agric4 ,expt4 ,sta41 #aiad1 ,bull4 #bgj4 #de ,melin1 ,e41 8,ueber die mykorrhizenpilze von ,pinus silvestris 7,l47 und ,picea abies 7,l471 ,karst40 ,svensk4 ,botan4 ,tidskr41 #aiba1 xv4 #df ,muntz1 ,a41 and ,coudon1 ,h41 8,la fermentation ammoniaque de la terre10 ,compt4 ,rend4 ,acad4 ,sci41 ,paris1 #ahic1 #aaf4 #dg ,neller1 ,j4 ,r41 8,studies on the ,correlation between the production of carbon dioxide and the accumulation of ammonia by soil organisms10 ,soil ,sci41 #aiah1 #e4 #dh ,otto1 ,h1 8,untersuchungen ber die ,auflsung von ,zellulosen und ,zellwnden durch ,pilze10 ,dissert41 ,berlin1 #aiaf4 #di ,perotti1 ,b41 8,uber das physiologische ,verhalten des ,dicyanamides mit ,rcksicht auf seinen ,wert als ,dngemittel10 ,centr4 f4 ,bakt41 #aijg1 ii1 #ah4 #ej ,peyronel1 ,b41 8,nuovi casa di rapporti micorizici tra ,basidiomiceti e ,fanerogame arboree10 ,bull4 ,soc4 ,bot4 ,ital41 #aibb4 #ea ,potter1 ,r4 ,s41 and ,snyder1 ,r4 ,s41 8,the production of carbon dioxide by moulds inoculated into sterile soil10 ,soil ,sci41 #aiah1 #e4 #eb ,povah1 ,a4 ,h4 ,w41 8,a critical study of certain species of ,mucor10 ,bull4 ,torrey ,bot4 ,club1 #aiag1 #dd4 #ec ,pratt1 ,o4 ,a41 8,soil fungi in relation to diseases of the ,irish potato in ,southern ,idaho10 ,journ4 ,agric4 ,res41 #aiah1 #ac4 #ed ,raistrick1 ,h41 and ,clark1 ,a4 ,b41 8,on the mechanism of oxalic acid formation by ,aspergillus niger10 ,biochem4 ,journ41 #aiai1 #ac4 #ee ,rayner1 ,m4 ,c41 8,nitrogen fixation in ,ericaceae10 ,bot4 ,gaz41 #aibb1 #gc4 #ef ,ritter1 ,g4 ,e41 8,contributions to the physiology of mould fungi10 ,voronege1 #aiaf4 #eg ,rosseels1 ,e41 8,l'influence des microorganismes sur la croissance des vgtaux suprieurs10 ,bull4 ,soc4 ,centrale ,forest4 ,belg41 #aiaf1 #bc4 #eh ,roussy1 ,a41 8,sur la vie des champignons en milieux ,gras10 ,compt4 ,rend4 ,acad4 ,sci41 ,paris1 #aiji1 #adi4 #ei ,scales1 ,f4 ,m41 8,the ,enzymes of ,aspergillus terricola10 ,journ4 ,biol4 ,chem41 #aiad1 #ai4 #fj ,schellenberg1 ,h4 ,c41 8,untersuchungen ber das ,verhalten einiger ,pilze gegen ,hemizellulosen10 ,flora1 #aijh1 #ih4 #fa ,schmitz1 ,h41 8,the relation of bacteria to cellulose fermentation induced by fungi with special reference to the decay of wood10 ,ann4 ,mo4 ,bot4 ,gard41 #aiai1 vi4 #fb ,shibata1 ,k41 8,uber das ,vorkommen vom ,amide spaltenden ,enzymen bei ,pilzen10 ,beitr4 ,chem4 ,physiol4 u4 ,path41 #aijd1 #e4 #fc ,ternetz1 ,c41 8ber die ,assimilation des atmosphrischen ,stickstoffs durch ,pilze10 ,jahrb4 f4 wiss4 ,bot41 #aijg1 #dd4 #fd ,verkade1 ,p4 ,e41 and ,shngen1 ,n4 ,l41 8,attackability of cis- and trans-isomeric unsaturated acids by moulds10 ,centr4 f4 ,bakt41 #aibj1 ii1 #ej4 #fe ,waksman1 ,s4 ,a41 8,soil fungi and their activities10 ,soil ,sci41 #aiaf1 #b4 #ff ,waksman1 ,s4 ,a41 8,the influence of available carbohydrate upon ammonia accumulation by micro-organisms10 ,journ4 ,amer4 ,chem4 ,soc41 #aiag1 #ci4 #fg ,waksman1 ,s4 ,a41 8,proteolytic enzymes of soil fungi and ,actinomycetes10 ,journ4 ,bact41 #aiah1 #c4 #fh ,waksman1 ,s4 ,a41 8,on the metabolism of ,actinomycetes10 ,proc4 ,soc4 ,amer4 ,bact4 ,abstract ,bact41 #aiai1 #c4 #fi ,waksman1 ,s4 ,a41 8,the influence of soil reaction upon the growth of ,actinomycetes causing potato scab10 ,soil ,sci41 #aibb1 xiv4 #gj ,waksman1 ,s4 ,a41 and ,cook1 ,r4 ,c41 8,incubation studies with soil fungi10 ,soil ,sci41 #aiaf1 #a4 ,,chapter ,,ix4 ,,the ,,invertebrate ,,fauna ,,of ,,the ,,soil 7,,other ,,than ,,protozoa74 ,the micro-organisms of the soil have been fully discussed in the preceding chapters of this volume4 ,there now remains to be considered the fauna of invertebrate animals1 other than protozoa1 which inhabit that same medium4 ,in the first place1 it is necessary to define what groups of invertebrate animals are to be regarded as coming under the category of soil organisms4 ,the latter expression has rather a wide application and1 for the present purpose1 is held to mean any organism of its kind which1 in some stage or stages of its life-cycle1 lives on or below the surface of the soil4 ,it will be obvious that1 with so comprehensive a definition1 the intimacy of the association of these animals with the soil will vary within very wide limits4 ,some animals pass their whole life-cycle in the soil2 others are only present during a limited phase1 and not necessarily in a trophic condition1 but since their occurrence is constant1 they cannot be entirely omitted from consideration4 ,unlike the groups of organisms which have been dealt with in the foregoing pages1 the invertebrates of the soil do not admit1 as a rule1 of investigation in culture media4 ,it is1 in consequence1 much more difficult to achieve in the laboratory the same control over their environmental conditions4 ,this fact in itself largely explains why the interpretations of field observations in animal ecology have not usually been subjected to the test of laboratory experimentation4 ,the study of animal ecology1 in so far as the denizens of the soil are concerned1 is of very recent birth4 ,it has not1 as yet1 passed the preliminary stage of cataloguing empirical data1 and much spade work will be necessary before the various factors controlling the phenomena actually observed are understood4 ,owing to the paucity of information available1 this chapter is essentially based upon observations conducted at ,rothamsted4 ,its object is not so much to attempt to evaluate the invertebrate fauna of the soil1 as to suggest a line of ecological work demanding investigation on land of many different types4 ,,method ,,of ,,investigating ,,the ,,soil ,,fauna4 ,the method adopted at ,rothamsted consists in taking weekly soil samples from a given area for a period of twelve months4 ,each sample is a cube of soil1 with a side dimension of nine inches1 and a total content of #gbi cubic inches4 ,the samples are taken by means of an apparatus consisting of four iron plates1 which are driven into the ground down to the required depth so as to form a kind of box1 which encloses a cube of soil 7vide ,morris1 #aibb ,a74 ,the latter is then removed in layers1 each layer being transferred to a separate bag for the purpose4 ,when the complete sample has been extracted1 there are five bags containing layers of soil taken from the surface to a depth of #a1 from #a to #c1 from #c to #e1 from #e to #g1 and #g to #i respectively4 ,below a depth of #i no samples have been taken4 ,the sample obtained in this manner may be gradually worked into small fragments by hand1 and examined whenever necessary under a binocular microscope for the smaller organisms present4 ,this procedure1 however1 is very tedious and has been replaced by the use of an apparatus consisting of a series of three sieves1 with meshes of decreasing size 7vide ,morris1 #aibb74 ,the soil is washed through these sieves by means of a stream of water1 and the meshes of the final strainer are small enough to retain all except the most minute organisms present1 while at the same time they allow the finest soil particles to be carried away4 ,when desirable1 the effluent can be passed through a bag or sieve of bolting silk1 in order to collect such organisms that may have passed through the third sieve4 ,in addition to the actual taking and examination of the samples1 a botanical survey of the area under investigation is made2 chemical and mechanical analyses of the soil are also required4 ,it is further necessary to take soil temperature readings1 to determine the moisture content of the samples taken1 and the amount of organic matter which they contain4 ,,groups ,,of ,,invertebrata ,,represented ,,in ,,the ,,soil4 ,the various groups of invertebrates represented in the soil may be briefly referred to in zoological order4 ,nematoda4--,the ,nematoda or thread-worms are chiefly animal parasites1 nevertheless they usually lead an independent existence in the soil in certain stages of their development4 ,the numerous small species belonging to the family ,anguillidid1 or eel-worms1 form a definite constituent of the soil fauna2 they are generally free-living and non-parasitic4 ,certain members of this family1 however1 are enemies of cultivated plants4 ,annelida4--,terrestrial ,annelida are almost entirely confined to the order ,oligochta1 the majority of which are earthworms 7,terricol71 whose whole life-cycle is passed within the confines of the soil4 ,the small white worms of the family ,enchytrid belong to the aquatic section 7,limicol7 of the order1 but they have various representatives which are abundant in damp soil containing organic matter4 ,mollusca4--,the terrestrial ,mollusca are included in the sub-order ,pulmonata of the ,gastropoda4 ,these organisms1 which include the snails 7,helicid7 and slugs 7,limacid71 regularly deposit their eggs in moist earth4 ,slugs adopt the soil as a frequent habitat1 only leaving it for feeding purposes in the presence of sufficient moisture4 ,they are frequent consumers of vegetation1 with the exception of ,testacella1 which is carnivorous4 ,crustacea4--,the few species of ,crustacea inhabiting the soil belong to the order ,isopoda1 family ,oniscid1 which are popularly referred to as 8woodlice10 8slaters10 etc4 ,myriapoda4--,the ,diplopoda or millipedes include enemies of various crops and are common denizens of the soil4 ,the ,chilopoda or centipedes are usually less abundant and are carnivorous4 ,the minute ,symphyla are often evident but are of minor importance4 ,insecta4--,insects form the dominant element in the invertebrate fauna4 ,phytophagous species devour the subterranean parts of plants1 and notable examples are afforded by the larv of ,melolontha1 ,agriotes and ,tipula4 ,saprophagous forms are abundantly represented by the ,collembola1 and by numerous larval ,diptera and ,coleoptera4 ,predaceous species preying upon other members of the soil fauna are exemplified by the ,carabid and many larval ,diptera4 ,parasitic species pass their larval stages on or within the bodies of other organisms4 ,the groups of ,hymenoptera1 and the dipterous family ,tachinid1 which exhibit this habit1 constitute1 along with predaceous forms1 one of the most important natural agencies controlling the multiplication of insect life4 ,there are also insects 7ants1 and other of the aculeate ,hymenoptera7 which utilize the soil as a suitable medium wherein to construct their habitations or brood chambers1 without necessarily deriving their food from the soil4 ,lastly1 there are many insects1 notably ,lepidoptera1 which only resort to the soil for the purpose of undergoing pupation4 ,the insect fauna is1 therefore1 a closely inter-connected biological complex2 for a discussion and an enumeration of its representatives reference may be made to papers by ,cameron 7#aiac1 #aiag71 and ,morris 7#aiba1 #aibb a74 ,arachnida4--,the two principal classes represented in the soil are the ,areinida1 or spiders1 and the ,acarina1 or mites1 and ticks4 ,the ,areinida1 which are well-known to be carnivorous1 are an unimportant constituent of the fauna4 ,acarina1 on the other hand1 are abundant1 and exhibit a wide range of feeding habits2 most of the soil forms are probably carnivorous1 and either free-living or parasitic4 ,,number ,,of ,,organisms ,,present ,,and ,,their ,,distribution ,,in ,,depth4 ,in computing the number of invertebrates normally present in a given type of soil1 the method adopted consists of making individual counts of all such organisms as occur in each sample of a series taken over a period of twelve months4 ,this method considerably reduces errors due to season and to the possible deviation of one or more samples from the average4 ,if the total number of these organisms is known for the samples taken1 it becomes a simple procedure to arrive at their approximate numbers per acre4 ,,table ,,xiv4 7,based on ,morris1 #aibb ,a47 ---------------------------------------- ------------------ ,unmanured ,plot4,manured ,plot4 ---------------------------------------- ------------------ ,insects #b1dgd1gjj #g1gbg1cjj ---------------------------------------- ------------------ ,larger ,nematoda and ,oligochta ,limicol #gid1fjj #c1fjj1djj ---------------------------------------- ------------------ ,myriapoda-- ,diplopoda #eif1jjj #a1cfg1jjj ,chilopoda #bae1djj #bjh1gjj ,symphyla #fd1jjj #bae1ejj ---------------------------- ,total #hge1djj #a1gia1bjj ---------------------------------------- ------------------ ,oligochta 7,terricol7 #deg1ijj #a1jaj1ajj ---------------------------------------- ------------------ ,arachnida-- ,acarina #bae1djj #eca1ijj ,areinida #bj1bjj #bj1bjj ---------------------------- ,total #bce1fjj #eeb1ajj ---------------------------------------- ------------------ ,crustacea 7,isopoda7 #cc1gjj #hj1hjj ---------------------------------------- ------------------ ,mollusca 7,pulmonata7 #ac1ejj #cc1gjj ---------------------------------------- ------------------ ,total ,invertebrata #d1hhe1djj #ad1gie1fjj ---------------------------------------- ------------------ ,illustration3 ,,fig4 #bj4--;,distribution in depth of the more important groups of soil invertebrates in the manured and unmanured 7or control7 plots at ,rothamsted4 7,from ,morris1 8,annals of ,applied ,biology10 vol4 ix41 nos4 #c and #d1 ,cambridge ,university ,press47 ,table ,,xiv4 represents a numerical estimate of the invertebrate fauna of two plots of arable land at ,rothamsted4 ,the soil is clay with flints overlying chalk1 and the land in question has been devoted for eighty years to continuous cropping with wheat2 one plot 7,no4 #c7 receives an annual dressing of farmyard manure at the rate of #ad tons per acre1 and the other plot 7,no4 #b7 receives no natural or artificial fertilizer4 ,the significant feature in a comparison of the fauna of the two plots is the great numerical increase in organisms due to the addition of manure4 ,from the point of view of distribution in depth1 ,fig4 #bj clearly demonstrates that the bulk of the fauna is concentrated in the first three inches of the soil4 ,with the exception of the ,acarina it is evident that the limits of vertical distribution extend below the depth of nine inches investigated1 although the numbers of organisms likely to be present are inconsiderable4 ,the ,oligochta1 or true earthworms1 occur in ,rothamsted soil in numbers very much in excess of the figures given by ,darwin1 who quoted observations by ,hensen4 ,the latter authority calculated that there were #ec1gfg earthworms in an acre of garden soil1 and estimated that about half that number would be present in an acre of corn field4 ,in the ,rothamsted investigations their numbers exceeded ,hensen's estimate over #af times in unmanured land1 and over #cf times in manured land4 ,in an area of pasture-land in ,cheshire few insects occurred below a depth of #b inches1 and they reached the limit of their vertical distribution at or near #f inches4 ,their number 7#c1ehf1jjj per acre7 is considerably in excess of that present in unmanured arable land at ,rothamsted4 ,illustration3 #a1 ,collembola2 #b1 ,thysanura2 #c1 ,orthoptera2 #d1 ,thysanoptera2 #e1 ,hemiptera2 #f1 ,lepidoptera2 #g1 ,coleoptera2 #h1 ,diptera2 #i1 ,hymenoptera4 ,,fig4 #ba4--,number of individuals in the different orders of insects in manured and unmanured arable land at ,rothamsted4 7,from ,morris1 8,annals of ,applied ,biology10 vol4 ix41 nos4 #c and #d1 ,cambridge ,university ,press47 ,,dominance ,,of ,,certain ,,species ,,and ,,groups4 ,in ,fig4 #ba a numerical analysis is given of the different orders of insects represented in ,rothamsted soil4 ,the ascendency of the ,hymenoptera and ,collembola is almost entirely due to the occurrence of three species in large numbers1 viz41 the ant ,myrmica lvinodis and the ,collembola1 ,onychiurus ambulans and ,o4 fimetarius4 ,in the unmanured plot these two ,collembola constituted #ac per cent4 of the insects and the species of ant accounted for nearly #bh per cent4 ,in the manured plot they amounted respectively to #bg per cent4 and #cf per cent4 of the insects present4 ,next in order of numerical ascendency are larval ,diptera1 mainly belonging to the families ,cecidomyid1 ,chironomid1 and ,mycetophilid4 ,the ,diptera are followed by the ,coleoptera1 whose most abundant representatives are larval ,elaterid 7wireworms74 ,illustration3 #a1 ,collembola2 #b1 ,thysanura2 #c1 ,orthoptera2 #d1 ,thysanoptera2 #e1 ,hemiptera2 #f1 ,lepidoptera2 #g1 ,coleoptera2 #h1 ,diptera2 #i1 ,hymenoptera2 #aj1 ,diplopoda2 #aa1 ,chilopoda2 #ab1 ,areinida2 #ac1 ,acarina4 ,,fig4 #bb4--,number of species of different orders of invertebrates present in the manured and unmanured 7or control7 plots at ,rothamsted4 7,from ,morris1 8,annals of ,applied ,biology10 vol4 ix41 nos4 #c and #d1 ,cambridge ,university ,press47 ,in point of view of number of species present 7,fig4 #bb71 ,coleoptera take the front rank2 in the unmanured plot they are very closely approached by ,collembola and ,diptera4 ,passing from the insects1 the next assemblage of organisms in point of number of individuals are the smaller worms4 ,the difficulties attending the specific identification of these organisms are great1 and1 in the present survey1 the ,nematodes and all the smaller ,oligochtes have not been separated4 ,the abundance of the ,myriapoda is mainly due to the prevalence of ,diplopoda1 which are represented by four species4 ,the ,chilopoda almost entirely consist of a single species ,geophilus longicornis4 ,the dominant group of the ,arachnida is the ,acarine family ,gamascid1 which are represented by about a dozen species4 ---------------------------------------- --------------------- ,phytophagous4,saprophagous4,carnivorous 4,heterophagous4 ---------------------------------------- --------------------- ,unmanured plot #ad #dh #ac #bj ,manured plot #ac #eh #i #bj ---------------------------------------- --------------------- ,,classification ,,of ,,soil ,,invertebrates ,,according ,,to ,,feeding ,,habits4 ,from the point of view of the fauna as a whole1 the zoological classification of the soil invertebrates is only significant when the various groups are analysed according to the feeding habits of their members4 ,all animals are directly or indirectly dependent upon plant life for their nutrition4 ,for the present purpose they are divided into four categories1 and the position of each class of animals in the scheme is based upon the habits of its chief representatives in the soil4 ,definite information on this subject1 however1 is not always forthcoming1 and it is only possible to achieve approximate estimates4 ,in the table above the percentages in number of individuals present in the two plots investigated at ,rothamsted are given under each type of feeding habit4 ,it must be borne in mind that these estimates only apply to average conditions2 the outbreak of a plant pest in any one year must naturally materially alter the proportions given4 ,the phytophagous organisms are represented by a certain number of the ,insecta together with the pulmonate ,mollusca4 ,carnivorous forms which are mainly beneficial from the agricultural standpoint1 include ,insecta1 together with the ,chilopoda1 many ,acarina and the ,areinida4 ,saprophagous forms constitute the dominant element of the soil fauna4 ,more than #cj per cent4 of the ,insecta exhibit this habit1 which is also the dominant one in the ,oligochta1 ,symphyla1 and in many of the soil ,nematodes4 ,heterophagous species include all those of somewhat plastic habits2 for the most part they are saprophagous1 but1 on the other hand1 a considerable proportion of the species attack growing plants or exhibit both habits4 ,under this category are included a certain number of the ,insecta1 the ,diplopoda1 ,isopoda1 and some ,acarina4 ,,the ,,influence ,,of ,,environmental ,,factors ,,upon ,,the ,,invertebrates ,,of ,,the ,,soil4 ,since animals are endowed with powers of independent locomotion3 they are not necessarily tied to their environment to the same extent that plants are4 ,the investigation of the influence of environmental factors sooner or later involves a study of the tropisms of the animals concerned4 ,until these are adequately understood it is scarcely possible to arrive at any exact conclusions relative to their behaviour in the soil4 ,insects1 for example1 respond to the stimuli of various1 and often apparently insignificant forces1 acting upon their sensory organs4 ,such responses are known as chemotropism1 phototropism1 hydrotropism1 thermotropism1 and so forth according to the nature of the stimuli4 ,tropisms are automatic and1 so far as they distinguish sensations1 are independent of any choice1 and consequently of psychic phenomena4 ,animal automatism1 however1 does not present the rigidity of mechanical automatism4 ,differential sensibility1 vital rhythms1 or periodicity1 etc41 are other important aspects of animal behaviour4 ,the environmental factors1 affecting more especially the insect population of the soil1 have been discussed by ,cameron 7#aiag7 and ,hamilton 7#aiag71 and certain broader aspects of animal ecology by ,adams 7#aiae7 and ,shelford 7#aiab74 ,these factors are so numerous and so inter-connected1 that it is only possible to refer to them briefly in the space available4 ,as might be expected1 soils that are of a light and open texture are the ones most frequented by soil insects1 nutritional and other factors being equal4 ,furthermore1 it has already been shown that in arable land insects and other animals penetrate to a greater depth than in pastures4 ,this fact is primarily due to the greater looseness of the soil occasioned by agricultural operations1 which ensure at the same time better drainage aeration1 and greater facilities for penetration4 ,hamilton found that soil insect larv are very sensitive to evaporation1 and especially so if the temperature is #bj ,c4 or over4 ,in their natural habitat the relative humidity of the air1 in moist or wet soil1 is not far below saturation1 and the temperature of the soil rarely goes above #bj-bc;,c41 and then only in exposed1 dry1 hard soil in which these larv do not occur4 ,the significance of the rate of evaporation as an environmental factor was first emphasised by ,shelford4 ,according to him the best and more accurate index of the varying physical conditions affecting land animals1 wholly or in part exposed to the atmosphere1 is the evaporating power of air4 ,by means of a porous cup-atmometer1 as devised by ,livingston1 ,shelford has carried out an important series of experiments on the reactions of various animals to atmospheres of different evaporation capacities1 and reference should be made to his text-book4 ,the importance of the organic matter present in the soil is well illustrated in the table on p4 #aeb4 ,the great increase in the number of insects and other animals is partly due to their direct introduction along with the manure1 and partly to their entry into the soil in response to chemotropic stimuli exerted by fermentation4 ,organic matter influences the fauna in other ways also2 it increases the moisture content of the soil1 and it provides many species with an abundance of food material4 ,also1 the amount of carbon dioxide present in the soil is partly dependent upon decaying organic matter4 ,hamilton conducted experiments on the behaviour of certain soil insects in relation to varying amounts of carbon dioxide4 ,although his work is of too limited a nature to be accepted without reserve1 it lends support to the conclusions of ,adams who says3 8,the animals which thrive in the soil are likely to be those which tolerate a large amount of carbon dioxide1 and are able to use a relatively small amount of oxygen1 at least for considerable intervals1 as when the soil is wet during prolonged rains4 ,the optimum soil habitat is therefore determined1 to a very important degree1 by the proper ratio or balance between the amount of available oxygen and the amount of carbon dioxide which can be endured without injury40 ,little is known concerning the occurrence of ammonia in the soil atmosphere1 but its presence in minute quantities is probably an important chemotropic factor in relation to saprophagous organisms which are the largest constituent of the fauna4 ,a great increase in ,dipterous larv occurs on the addition of farmyard manure1 and this is noteworthy in the light of ,richardson's experiments 7#aiaf71 which indicate that ammonia exercises a marked attraction for ,diptera1 which spend some part of their existence in animal excrement in some form or another4 ,the nature of the vegetation supported by the soil is of paramount importance in relation to phytophagous organisms1 and examples need scarcely be instanced of certain species of soil insects being dependent upon the presence of their specific food plants4 ,,the ,,relation ,,of ,,soil ,,invertebrates ,,to ,,agriculture4 ,the relation of these organisms to agriculture may be considered from three points of view3 7a7 their influence upon the soil itself2 7b7 their relation to the nitrogen cycle2 and 7c71 their direct influence upon economic plants4 7a7 ,the behaviour of earthworms as a factor inducing soil fertility is discussed by ,darwin in his well-known work on the subject1 and their action may be briefly summarised as follows4 ,in feeding habits they are very largely saprophagous1 and consume decaying vegetable matter including humus1 which they swallow1 together with large quantities of soil4 ,earthworms come to the surface to discharge their fces 78worm casts071 and in this process they are continually bringing up some of the deeper soil to the air4 ,darwin estimated that earthworms annually brought to the surface of the soil in their 8casts0 sufficient earth to form a layer #b inch in depth1 or #aj tons per acre4 ,their action1 along with the atmosphere1 are the chief agencies which produce the uniformity and looseness of texture of the surface soil4 ,by means of their burrows earthworms facilitate the penetration of air and water into the soil1 while their habit of dragging leaves and other vegetable material into these burrows increases the organic matter present below the surface4 ,these facts are generally agreed upon1 but it is a disputed point whether earthworms1 by devouring organic matter1 aid the conversion of the latter into plant food more rapidly than takes place solely through the activities of micro-organisms4 ,soil insects and other arthropods1 by their burrowing activities1 are also instrumental in loosening the soil texture and thereby facilitating soil aeration and the percolation of water4 ,the action of termites in warmer countries is discussed by ,drummond in his 8,tropical ,africa10 who compares the rle of subterranean termites to that of earthworms4 ,the great abundance of ants renders them also significant in this same respect1 and very few species are direct enemies of the agriculturist4 ,illustration3 ,,fig4 #bc4--;,diagram showing the ,relation of the ,soil ,invertebrata 7other than ,protozoa7 to the ,nitrogen ,cycle4 7b7 ,in their relation to the nitrogen cycle 7vide p4 #agd71 the activities of the soil invertebrates may be expressed diagrammatically1 as a side-chain in the process 7,fig4 #bc74 ,the proteins1 elaborated by plants1 are utilised as nitrogenous food by the phytophagous animals present4 ,the waste products of the latter1 which contain the nitrogen not used for growth or the replacement of loss by wear and tear1 are returned to the soil4 ,here they disintegrate1 and are ultimately converted into ammonium salts1 mainly by bacterial action4 ,the dead bodies of these animals are also broken down by various means1 becoming eventually chemically dissociated and available as plant food4 ,animal 7and plant7 residues serve1 however1 as food for the large number of saprophagous invertebrates present in the soil4 ,in this event the nitrogen contained in such residues becomes 8locked up10 as it were1 for the time being in their bodies4 ,both saprophagous and phytophagous animals are preyed upon by carnivorous species1 but ultimately the nitrogen is returned to the soil upon the death of those organisms4 ,the amount present in the bodies of the whole invertebrate fauna has been calculated by ,morris 7#aibb7 upon analyses furnished by chemists at ,rothamsted4 ,it is estimated that the fauna of manured land contains about #gcdi grm41 or #afb lb4 of nitrogen per acre1 and that of untreated land1 #cdij grm41 or #ge lb4 per acre4 ,these amounts are equal respectively to the nitrogen content of #ajcf lb4 and #dh lb4 of nitrate of soda4 ,the primary question affecting agriculture is1 whether any notable loss of nitrogen is occasioned by the presence of these organisms in the soil4 ,it has been mentioned that their nitrogenous waste material1 and their dead bodies1 ultimately undergo disintegration2 any loss1 if any1 takes place during the latter process4 ,with the more complex compounds it probably consists in the production of amino-acids and their subsequent hydrolysis or oxidation4 ,during this process an appreciable loss of nitrogen in the gaseous form occurs4 ,this loss1 which is discussed on p4 #agc would represent the net deficit occasioned by the incidence of invertebrates in the soil4 ,against this loss must be placed the beneficial action of such organisms as earthworms1 which1 in all probability1 more than counterbalances it4 7c7 ,many soil insects1 on account of their phytophagous habits1 are well-known to be some of the most serious enemies of agriculture4 ,certain of these1 and also other classes of invertebrates1 which are likewise directly injurious1 have been instanced in the earlier pages of this chapter4 ,detailed information on this subject will be found in textbooks of economic zoology1 notably the volume by ,reh 7#aiac74 ,,literature ,,referred ,,to4 ,,adams1 ,c4 ,c41 8,an ,ecological ,study of ,prairie and ,forest ,invertebrates10 ,bull4 ,illin4 ,st4 ,lab4 ,nat4 ,hist41 #aiae1 xi4 ,,cameron1 ,a4 ,e41 8,general ,survey of the ,insect ,fauna of the ,soil10 ,journ4 ,econ4 ,biol41 #aiac1 viii4 8,insect ,association of a ,local ,environmental ,complex in the ,district of ,holmes ,chapel1 ,cheshire10 ,trans4 ,roy4 ,soc4 ,edin41 #aiag1 lii4 ,,darwin1 ,c41 8,vegetable ,mould and ,earthworms10 ,london1 #ahha4 ,,hamilton1 ,c4 ,c41 8,the ,behaviour of some ,soil ,insects in ,gradients of ,evaporating ,power of ,air1 etc410 ,biol4 ,bull41 #aiag1 xxxii4 ,,morris1 ,h4 ,m41 8,observations on the ,insect ,fauna of ,permanent ,pasture in ,cheshire10 ,ann4 ,app4 ,biol41 #aiba1 vii4 8,on a ,method of ,separating ,insects and other ,arthropods from ,soil10 ,bull4 ,entom4 ,res41 #aibb1 xiii4 8,the ,insect and ,other ,invertebrate ,fauna of ,arable ,land at ,rothamsted10 ,ann4 ,app4 ,biol41 #aibb ,a1 ix4 ,,reh1 ,l41 ,in ,sorauer's 8,pflanzenkrankheiten10 #aiac1 iii4 ,,richardson1 ,c4 ,h41 8,the ,attraction of ,diptera to ,ammonia10 ,ann4 ,ent4 ,soc4 ,amer41 #aiaf1 ix4 ,,russell1 ,e4 ,j41 8,the ,effect of ,earthworms on ,soil ,productiveness10 ,journ4 ,agric4 ,sci41 #aiaj1 iii4 ,,shelford1 ,v4 ,e41 8,animal ,communities in ,temperate ,america10 ,chicago4 #aiad1 8,the ,importance of the ,measure of ,evaporation in ,economic ,studies of ,insects10 ,journ4 ,econ4 ,entom41 #aiab1 vii4 ,,chapter ,x4 ,,the ,,chemical ,,activities ,,of ,,the ,,soil ,,population ,,and ,,their ,,relation ,,to ,,the ,,growing ,,plant4 ,in the preceding chapters it is shown that the soil is normally inhabited by a very mixed population of organisms1 varying in size from the smallest bacteria up to nematodes and others just visible to the unaided eye1 on to larger animals1 and finally earthworms1 which can be readily seen and handled4 ,these organisms all live in the soil1 and therefore must find in it the conditions necessary for their growth4 ,we have dealt in the first chapter with the supplies of water1 air1 and heat1 without which life is clearly impossible4 ,equally necessary is the source of energy1 for the organism requires energy material as surely as the motor engine requires petrol1 and it ceases to function unless an adequate supply is forthcoming4 ,all the energy comes in the first instance from the sun1 if we exclude the unknown but probably small fraction coming from radio-active elements4 ,but this radiant energy is not utilisable by the soil population1 excepting surface alg2 it has to be transformed into another kind4 ,so far1 chlorophyll is the only known transformer2 it fixes the energy of sunlight and stores it up in bodies like hemicellulose1 sugar1 starch1 protein1 etc4 ,the transformation is imperfect2 even the heaviest yielding crops grown under glass1 in conditions made as favourable as our knowledge permits1 utilise only about #d per cent4 of the total energy available during their period of growth2 in natural conditions not more than #jd per cent4 is utilised4 ,such as it is1 however1 the energy fixed in the plant represents all1 indeed more than all1 that the soil organisms can obtain4 ,in the state of ,nature1 vegetation dies and is left on the soil4 ,two things may then happen4 ,it may become drawn into the soil by earthworms and other agents2 the energy supply is thus distributed in the soil to serve the needs of the varied soil population4 ,this is the normal case1 associated with the normal soil population and the normal flora4 ,if1 however1 the mingling agents are absent1 the dead vegetation lies like a mat on the surface of the soil1 only partially decomposing1 unsuitable for the growth of most seedlings1 and effectually preventing most of the vegetation below from pushing a way through3 thus there comes to be no vegetation at all1 or only a very restricted and special flora4 ,the soil population becomes also specialised4 ,peats and acid grassland afford examples4 ,on the neutral grass plots at ,rothamsted1 the dead vegetation does not accumulate on the surface but is rapidly decomposed or drawn into the soil1 leaving the surface of the earth bare and free for the growth of seedlings4 ,on the acid plots dead vegetation remains long on the surface1 blotting out all new growth excepting two or three grasses which form underground runners capable of penetrating the mat1 and sorrel1 the seedling roots of which seem to have the power of boring through a fibrous layer of this sort4 ,it is possible to remove the mat entirely by bacterial action alone1 if sufficient lime be added periodically to make the reaction neutral1 but failing these repeated additions the mat persists4 ,we shall confine ourselves to the normal case where earthworms bring the source of energy into the soil4 ,directly the energy is available1 it begins to be utilised4 ,two laws govern the change4 ,the first is well-known to biologists3 it states that the total energy of the system remains constant and can neither be increased nor diminished except from outside2 in other words1 that energy can be neither created nor destroyed4 ,the second law is less familiar3 it is that energy once transformed to heat by one organism cannot be used again by another4 ,it is not destroyed2 it remains intact1 but is useless to the organism4 ,one cannot have an indefinite chain of organisms living on each other's excretory products2 there was a certain quantity of energy in the food eaten by the first1 and no more than this quantity can be got out whether one organism obtains the whole or whether others share it4 ,the outside value for the amount of energy fixed in the soil is obtainable by combustion of the soil in a calorimeter1 but much of this is not available to the soil organisms4 ,the normal sedimentary soils of ,england still contain decomposition products of the dbris of plants and animals originally deposited with them1 but in the long course of ages much of the extractable energy has been utilised4 ,the soil population is thus dependent on recently grown vegetation1 and it is therefore largely confined to the layer1 usually in this country about #f inches thick1 through which the recently dead vegetation is distributed4 ,below this level there may be sufficient air1 water1 temperature1 etc41 but there is insufficient source of energy for any large population4 ,unfortunately there is no ready means for distinguishing between the total and the actually available quantity of energy in the soil4 ,but it is not difficult1 by adopting the ,rothamsted analytical method1 to ascertain the approximate amount of energy that has been transformed in a given period4 ,the ,rothamsted plots are periodically analysed and a balance sheet is drawn up showing how much of each constituent has been added to and removed from the soil in the intervening period4 ,for two of the ,broadbalk plots the results are shown in ,tables ,,xv41 ,,xvi4 ,the dunged plot receives #ad tons farmyard manure per annum1 a quantity in excess of what would usually be given2 the unmanured plot1 on the other hand1 has received no manure for many years and is abnormally poor4 ,normal soils lie somewhere between these limits1 but tending rather to the value for the dunged than for the unmanured plot4 ,it will be seen that each acre of the dunged land loses on an average #da1jjj calories per day1 while each acre of the unmanured land loses on an average #bgjj calories per day4 ,,table ,,xv4--,,material ,,balance ,,sheet3 ,,broadbalk ,,soil1 ,,rothamsted4 7,,lb4 ,,per ,,acre ,,per ,,annum47 ---------------------------------------- ------------- ,farmyard ,no ,manure ,manure ,added4 ,added4 -------------------------- ,c4 ,n4 ,c4 ,n4 ---------------------------------------- ----------- ,added in farmyard manure #cfjj #bjj nil nil ,added in stubble #cjj #c #ajj #a ---------------------------------------- ----------- ,total added #cijj #bjc #ajj #a ,taken from soil nil nil #bjj nil ,stored in soil #bjj #cj nil nil ---------------------------------------- ----------- ,lost from soil #cgjj #agj #cjj nil,h ,per cent4 #ie #hd #ajj nil ---------------------------------------- ----------- ,initial ,c 3 ,n ratio in farmyard manure1 #ah 3 #a ,final ,c 3 ,n ratio in soil1 #aj 3 #a4 ,h ,gain of #f lb4 ,see p4 #agc4 ,,table ,,xvi4--,,annual ,,energy ,,changes ,,in ,,soil3 ,,broadbalk4 ,,approximate ,,values ,,only4 ,,millions ,,of ,,kilo ,,calories ,,per ,,acre ,,per ,,annum4 ---------------------------------------- --------------- ,farmyard ,no ,manure ,manure ,added4 ,added4 ---------------------------------------- --------------- ,added in manure #ad nil ,added in stubble #b #jc ---------------------- ,total added #af #jc ,taken from soil nil #je-a ,stored in soil #je-a nil ---------------------- ,dissipated per annum #ae #a ---------------------------------------- --------------- ,per day3 calories #da1jjj #bgjj ,equivalent to #ab men4 man4 ,the human food grown provides for #b men4 man4 ---------------------------------------- --------------- ,these numbers are interesting when we reflect that the human food produced on the dunged land yields only #gjjj calories per day1 from which it is clear that our agricultural efforts so far provide more energy for the soil population1 for which it was not intended1 than for ourselves4 ,the account is not complete2 we have omitted all reference to the oxidation of ammonia and of elements other than carbon4 ,nature seems to be in an unexpectedly economical mood in the soil1 and all compounds which can be oxidised with liberation of energy seem to have corresponding organisms capable of utilising them4 ,even phenol1 benzene1 hydrogen1 and marsh gas can all be oxidised and utilised as energy sources by some of the soil population4 ,even with this remarkable power the soil population has insufficient energy to satisfy all its possibilities2 our present knowledge indicates that energy supply is1 in this country at any rate1 the factor limiting the numbers of the population4 ,increases in the water supply or the temperature of the soil produce no consistent effect on the population1 but directly the energy supply is increased the numbers at once rise4 ,,material ,,changes4 ,these transformations of energy involve transformations of matter4 ,the original plant residues may be divided roughly into substances forming the structure of the plant1 such as the hemicelluloses1 the pentosans1 gums1 and the contents of the cell--the protoplasm and the storage products1 protein2 in addition1 there are smaller quantities of fats and waxes and other constituents4 ,some of the easily-decomposable carbohydrates never reach the soil at all1 being broken down by intracellular respiration or attack of micro-organisms4 ,but much of the structure material--hemicelluloses1 pentosans1 etc4--remains4 ,once the plant residues pass through the earthworm bodies they become completely disintegrated and lose all signs of structure4 ,the only visible product so far known is humus1 the black sticky substance characteristic of soil and of manure4 ,two modes of formation have been suggested4 ,carbohydrates1 sugars1 pentosans1 etc41 are known to yield furfuraldehyde or hydroxymethylfurfuraldehyde on decomposition1 and it has been shown at ,rothamsted that this readily condenses to form a humus-like body1 if not humus itself4 ,in the laboratory the reaction is effected in presence of acid1 but even amino-acids suffice4 ,all the necessary conditions occur in the soil1 and humus formation may proceed in this way4 ,some of the structure material--the lignin--contains aromatic ring groupings4 ,fischer and ,schrader have shown that in alkaline conditions these ring substances absorb oxygen and form something very like humus4 ,it is quite possible that humus formation also proceeds in the soil in this way4 ,whether the two products are chemically identical is not known4 ,the scheme can be represented thus3-- ,cell structure material -------------------------------- ,aliphatic ,aromatic 7,hemicelluloses1 7,lignin1 etc41 ,pentosans1 etc47 in presence of oxygen and under ------------------- aerobic conditions7 ,fatty acids ,furfuraldehyde or ,hydroxymethylfurfuraldehyde 7in presence of acid7 ,calcium carbonate4 ,humus4 ,the disintegration of the cell and the first stages in the decomposition of the structure material are almost certainly brought about by micro-organisms4 ,whether they complete the process is not known3 purely chemical agencies could easily account for part4 ,the decomposition of protein in the soil has not been studied in any detail4 ,from what is known of the acid hydrolysis and the putrefactive decompositions1 however1 it is not difficult to draw up a scheme which1 at any rate1 accords with the facts at present known4 ,it is probable that the protein gives rise to amino-acids1 which then break down by one of the known general reactions4 ,two types of non-nitrogenous products may be expected3 ,the aliphatic amino-acids give rise to ammonia and fatty acids2 these form calcium salts which break down to calcium carbonate4 ,the aromatic amino-acids--tyrosin1 phenylalanine1 etc4--which would account for about #f per cent4 of the nitrogen of vegetable proteins1 would be expected to give ammonia and phenolic substances4 ,now phenols are poisonous to plants and if no method existed for their removal the accumulation would ultimately render the soil sterile4 ,matters would be even worse on cultivated soils1 since cows' urine1 which enters into the composition of farmyard manure and is the chief constituent of liquid manure1 contains1 according to ,mooser1 no less than #jbe to #jgg grams of p-cresol per litre1,i a quantity three to ten times that present in human urine4 ,fortunately this contingency never arises1 for the soil contains a remarkable set of organisms capable of decomposing the phenols and leaving the soil entirely suitable for plant growth4 ,this affords an interesting case of an organism--in this case the plant--growing well in a medium in spite of some adverse condition1 not because it is specially adapted to meet this condition1 but because some wholly different agent removes it4 ,i ,mooser1 ,zeitschrift physiol4 ,chem41 #aiji1 lxiii41 #agf4 ,no phenol was found4 ,it is possible that the p-cresol is not entirely derived from the protein1 but that some comes from the glucosides in the animals' food4 ,other ring compounds1 e4g4 pyrrol1 arise in smaller quantity in the decomposition of protein1 but their fate in the soil is not known4 ,we may summarise the probable changes of the protein as follows3-- ,protein4 ------------------------------------- ,aliphatic ,aromatic ,other amino-acids amino-acids compounds 7,pyrrol1 etc47 ---------------- ---------------- ,fatty acids and ,ammonia ,phenolic hydroxy acids compounds ,nitrite ,calcium ,nitrate ,,co carbonate ,it must be admitted that the evidence is indirect4 ,the rate of oxidation of ammonia by bacteria in the soil is more rapid than the rate of formation1 so that ammonia is practically never found in the soil in more than minimal amounts 7#a or #b parts per #a1jjj1jjj72 indeed1 the only evidence of its formation was for a long time the fact that no compound other than ammonia could be oxidised by the nitrifying organism4 ,it has1 however1 since been shown at ,rothamsted that ammonia accumulates in soils in which the nitrifying organism has been killed4 ,nothing is known of the mechanism of the oxidation of ammonia beyond the fact that it is biological2 the reaction is not easily effected chemically at ordinary temperatures4 ,possibly the organism assimilates ammonia at one end of a chain of metabolic processes and excretes nitrates at the other4 ,or1 the reaction may be simply a straight oxidation for energy purposes1 the ammonia changing to hydroxylamine and then to nitrous and nitric acids4 ,the nitrate does not remain long in the soil4 ,some is taken up by the plant and some is washed out from the soil4 ,part1 however1 either of the nitrate itself or of one of its precursors is converted into an insoluble form3 probably it is changed into protein by the action of micro-organisms2 it then goes through the whole process once more4 ,these are the general outlines2 they present no particular chemical difficulties4 ,when we come to details1 however1 there is much that cannot be understood4 ,first of all1 there is the slow rate at which complex nitrogen compounds disappear from the soil in comparison with the rate of oxidation of the carbon4 ,thus1 in the original plant residues1 there is some forty times as much carbon as nitrogen3 before they have been long in the soil there is only ten times as much carbon as nitrogen2 this seems to be the stable position4 ,what is the reason for this preferential oxidation of the carbon8 ,no explanation can yet be given4 ,illustration3 ,,fig4 #bd4 ,x-axis3 #ahhg-h #ahij-a #aijj-a #aiaj-aa ,y-axis3 per acre ,an equally difficult problem arises in connection with the length of time the process will continue4 ,decomposition of the nitrogen compounds never seems to be complete in the soil2 it dribbles on interminably4 ,in the year #ahgj ,lawes and ,gilbert cut off a block of soil from its surroundings and undermined it so that the drainage water could be collected and analysed4 ,the soil has been kept free from vegetation or addition of nitrogen compounds from that time till now2 yet it has never failed to yield nitrates1 and the annual yield falls off only very slowly 7,fig4 #bd74 ,this same peculiarity is seen in the yield of crops on unmanured land3 it decreases1 but very gradually2 even after eighty years the process is far from complete1 and there is no sign that it will ever come to an end4 ,,table ,,xvii4--,,approximate ,,loss ,,of ,,nitrogen ,,from ,,cultivated ,,soils3 ,,broadbalk ,,wheat ,,field1 ,,rothamsted1 ,,forty-,,nine ,,years 7#ahfe-aiad47 ---------------------------------------- -------------------------- ,rich ,soil3 ,plot #b4 ,poor ,soil3 ,plot #c4 ,lb4 per ,acre4 ,lb4 per ,acre4 ---------------------------------------- -------------------------- ,nitrogen in soil in #ahfeage per cent4 #dcdjaje per cent4 #bgbj ,nitrogen added in manure1 rain 7#e lb4 per annum71 and seed 7#b lb4 per annum7 #aj1adj #cdj ---------------------------------------- -------------------------- ,nitrogen expected in #aiad #ad1dhj #cjfj ,nitrogen found in #aiad #bei per cent4 #eiejjie per cent4 #beij ---------------------------------------- -------------------------- ,loss from soil #hecj #dgj ,nitrogen accounted for in crops #bejj #gej ---------------------------------------- -------------------------- ,balance1 being dead loss #fjcj -#bhj;,j ,annual dead loss #abc - #f;,j ---------------------------------------- -------------------------- ,j ,gains4 ,possibly the result of bacterial action4 ,a further remarkable fact connected with the decomposition of the nitrogen compounds is that it seems invariably to be accompanied by an evolution of gaseous nitrogen4 ,apparently there are two cases4 ,under anaerobic conditions many of the soil organisms have the power of obtaining their necessary oxygen from nitrates1 thereby causing a change in the molecule which leads in some cases to liberation of gaseous nitrogen2 but the same result seems to be attained in aerobic conditions1 especially when carbon is being rapidly oxidised4 ,it is possible that the reaction is the same1 and that in spite of the general aerobic conditions there is locally an anaerobic atmosphere4 ,but it is also possible that some direct oxidation of protein or amino-acids may yield gaseous nitrogen4 ,however it is brought about it affects a considerable proportion of the entire stock of nitrogen1 and it becomes more serious as cultivation is intensified4 ,thus1 on the ,broadbalk plot receiving farmyard manure the loss is particularly heavy2 on the unmanured plot it cannot be detected4 ,the nitrogen balance-sheet is shown in ,table ,,xvii4 ,the oxidation of carbonaceous matter1 however1 is not invariably accompanied by a net loss of nitrogen2 in other circumstances there is a net gain4 ,in natural conditions there seems always to have been some leguminous vegetation growing2 the gain may1 therefore1 be ascribed to the activity of the nodule organism4 ,in pot experiments1 however1 it has been found possible1 by adding sugar to the soil1 to obtain gains of nitrogen where there is no leguminous vegetation1 and this is attributed to the activity of ,azotobacter4 ,the nitrogen cycle as observed in the soil is as follows3-- -------------- ,protein ---------------- ,by certain organisms ,by ,azotobacter1 and by ,clostridium1 growing ,ammonia ,mechanism nodule organisms1 plants uncertain etc4 ,nitrite ,gaseous ------- ,nitrate ------ ,nitrogen -------- ,by denitrifying organisms ,there has been but little study of the process of decomposition of the other compounds in plants4 ,part1 if not all1 of the sulphur is known to appear as sulphate1 and some of the phosphorus as phosphate4 ,it is certain that the plant constituents decompose1 for there is no sign of their accumulation in the soil4 ,they may exert transitory effects1 but there is nothing to show permanent continuance4 ,the toxic conditions which cause trouble in working with pure cultures of organisms in specific cultures media do not1 so far as is known1 arise in the soil4 ,all attempts to find bacterio-toxins or plant toxins in normal soils have failed4 ,the product toxic to one organism seems to be a useful nutrient to another1 and so the mixed population keeps the soil healthy for all its members4 ,there is little precise knowledge as to the part played by the different members of the soil population in bringing about these changes4 ,we know in a general way that earthworms effect the distribution of the plant residues in the soil1 and serve to disintegrate them2 there is no evidence1 however1 that they play any indispensable part in the decomposition4 ,many root and other fragments do not go through this process2 observation shows that fungi can force a way in1 and they may be followed by nematodes which continue the disintegration4 ,possibly some of the flagellates help1 and certainly the bacteria do4 ,after that nothing is certain4 ,we cannot1 with certainty1 assign any particular reaction in the decomposition to any specific organism1 with the exception of the oxidation of the phenolic substances1 the conversion of ammonia to nitrite and nitrate1 and the fixation of nitrogen4 ,with these exceptions many organisms seem capable of bringing about the reactions1 and indeed some of the reactions may be purely chemical and independent of biological agencies4 ,the relationships between the soil population and soil fertility are readily stated in general outline1 but they are by no means clear cut when one comes to details2 fertility is a complex property1 and some of its factors are independent of soil micro-organisms4 ,the general relationship between plants and soil organisms is one of complete mutual interdependence4 ,the growing plant fixes the sun's energy and converts it into a form utilisable by the soil organisms2 without the plant they could not exist4 ,the plant is equally dependent on the soil organisms in at least two directions3 their scavenging action removes the dead vegetation which would1 if accumulated on the surface of the soil1 effectively prevent most plants from growing4 ,further1 the plant is dependent on the soil population for supplies of nitrates4 ,nothing is known about the relative efficiencies of the various soil organisms as scavengers4 ,numerous fungi and bacteria are effective producers of ammonia1 the precursor of nitrates2 it is not known1 however1 whether flagellates and such higher forms as nematodes act in this way4 ,this widespread power of producing ammonia makes it impossible in our present knowledge to regard any particular group of organisms as par excellence promoters of fertility4 ,indeed1 it is safest not to attempt to do so4 ,the primary purpose of the activities of a soil organism is to obtain energy and cell material for itself2 any benefit to the plant is purely incidental4 ,for cell material it must have nitrogen and phosphorus2 here it competes with the plant4 ,if it produces more ammonia than it utilises--in other words1 if it is driven to nitrogen compounds for its energy1 then the plant benefits4 ,if1 on the other hand1 it absorbs more ammonia than it produces1 as happens when it derives its energy from non-nitrogenous substances1 the plant suffers4 ,thus1 addition of peptone to the soil or an increase in bacterial numbers effected without addition of external energy 7e4g4 by partial sterilisation7 leads to increased ammonia supply1 and1 therefore1 to increased fertility4 ,but addition of sugar to the soil causes so great an increase of numbers of bacteria and other organisms that considerable absorption of ammonia and nitrate occurs1 and fertility is for a time depressed4 ,both actions proceed in soils partially sterilised by organic substances1 such as phenol1 which are utilised by some of the soil organisms2 there is first a great rise in numbers of these particular organisms with a depression of ammonia and nitrate1 then a drop to the new level1 higher than the old one1 and an increased production of ammonia and nitrate resulting from the partial sterilisation effects4 ,we must then regard the soil population as concerned entirely to maintain itself1 and only incidently benefiting the plant1 sometimes1 indeed1 injuring it2 always essential1 yet always taking its toll1 and sometimes a heavy toll1 of the plant nutrients it produces4 ,this effect makes it difficult to deduce simple quantitative relationships between bacterial activity and soil fertility1 and the difficulty is increased by the fact that bacteria and plants may both be injured or benefited by the same causes1 so that high bacterial numbers in a fertile soil would not necessarily be the cause1 but might be simply the result of fertility4 ,the circumstance that certain soil organisms--bacteria1 alg1 and fungi--themselves assimilate ammonia and nitrate may account for the remarkable slowness of nitrate accumulation1 to which reference has already been made4 ,the protein formed from the assimilated nitrogen remains in the bodies of the organisms1 living or dead1 till decomposition sets in4 ,it is not difficult to picture a cycle of events in which much of the nitrate formed is at once reabsorbed by other organisms1 and only little is actually thrown off into the soil4 ,such a process might continue almost interminably so long as any carbonaceous material remained4 ,finally1 we come to the very interesting problem--is it possible to control the population of the soil8 ,the problem may seem superfluous in view of the difficulties just mentioned4 ,some aspects of it1 however1 are fairly clearly defined4 ,in the first instance1 some organisms appear to be wholly harmful to the plant2 among them are parasitic eelworms and fungi1 and bacteria causing disease4 ,control of these organisms can be brought about by partial sterilisation1 and of all methods heat is the most effective1 but it is costly1 and attempts are now being made to replace it by chemical treatment4 ,the results are promising1 but the investigation is laborious2 the organisms show specific relationships1 and in finding a sufficiently potent and convenient poison it is necessary in each case to make an investigation into the relationship between chemical constitution and toxicity to the particular organism concerned4 ,formaldehyde is usually potent against fungi1 and the cresols1 and particularly their chlor- and chloronitro-derivatives1 are potent against animals 7eelworms1 etc474 ,one group of organisms is wholly beneficial1 those associated with leguminous plants4 ,attempts have been made to increase their activities by inoculating the soil with more vigorous strains4 ,the practical difficulties still remain very considerable1 but there is hope that they may be overcome4 ,it is also possible to shift the balance of the soil population in certain directions4 ,special groups of soil organisms can be caused to multiply temporarily1 if not permanently1 by satisfying their particular requirements4 ,thus1 when a soil has been heated above #ajj ,c4 it becomes specially suited to the growth of fungi1 and quite unsuited to certain bacteria such as the nitrifying organisms and others2 if this heated soil is infected with a normal soil population the fungi develop to a remarkable extent4 ,the nodule organisms appear to be stimulated by addition of farmyard manure and of phosphates1 and the phenol-destroying organisms by successive small additions of phenol4 ,finally1 quite apart from the control of disease organisms1 it is possible to alter the soil population considerably by partial sterilisation1 using a temperature of only about #fj ,c41 or a poison like toluene that favours few of the soil organisms4 ,this problem has already been discussed in ,chapter ,i4 ,the control of the soil population is still only in its infancy1 but it already promises useful developments4 ,it cannot1 however1 be too strongly insisted that the only sure basis of control is knowledge1 and we cannot hope to push control further till we have learned much more about the soil population than we know at present4 ,,author ,,index4 ,,adametz1 #aah4 ,adams1 #aeh4 ,aiyer1 #aac4 ,appel1 #acc4 ,artari1 #ajg4 ,ashby1 #db4 ,,barthel1 #bd4 ,beijerinck1 #f1 #cg1 #da1 #db1 #df1 #ajg4 ,berthelot1 #e1 #f1 #da4 ,bewley1 #dg1 #ea1 #acb4 ,bezssonoff1 #fi4 ,boas1 #ach4 ,bokorny1 #ach4 ,bonazzi1 #de4 ,boresch1 #ajg4 ,boussingault1 #c4 ,bredemann1 #bd4 ,bristol1 #ajf4 ,brizi1 #aac4 ,brown and ,halversen1 #abg4 ,burgess1 #da4 ,burrill1 #dh4 ,bussey1 ,peters and ,ulrich1 #acb4 ,butkevitch1 #ach1 #aci4 ,butler1 #acb4 ,,cameron1 #aej1 #aeh4 ,chodat1 #ajg4 ,christensen1 #df4 ,clayton1 #bh1 #dc4 ,coleman1 #abg1 #acf4 ,conn1 #bc1 #ed1 #fa1 #abc4 ,cramer1 #ci4 ,crump1 #eg1 #gi1 #hj4 ,cunningham1 #fi4 ,cutler1 #eg1 #eh1 #gh1 #hj4 ,,dale1 #aah1 #aba4 ,darwin1 #aec4 ,dascewska1 #acd4 ,de ,bruyn1 #acb4 van ,delden1 #db4 ,delf1 #hg4 ,doryland1 #cc1 #dj4 ,dox1 #ach4 ,dox and ,neidig1 #acd4 ,drummond1 #afj4 ,duggar and ,davis1 #ace4 ,duvaine1 #bj4 ,,ehrenberg1 #ach4 ,ehrlich and ,jacobsen1 #ach4 ,esmarch1 #ajb1 #ajc4 ,,fabricius1 #fa4 ,feilitzen1 #fa4 ,fischer1 #aah1 #abf4 ,forte1 #aja4 ,frank1 #acb4 ,fritsch1 #aab4 ,,gainey1 #df4 ,gillespie and ,hurst1 #adj4 ,goddard1 #aah1 #abj1 #aba4 ,golding1 #di4 ,goodey1 #fh1 #gc1 #gi1 #aje4 ,greaves1 #db1 #fa4 ,green1 #cg4 ,grintzesco1 #ajg4 ,groenewege1 #db4 ,,hagem1 #aah1 #aba1 #acf1 #ach1 #aci4 ,hamilton1 #aeh1 #aei4 ,hansen1 #dh4 ,hanzawa1 #dc4 ,harrison1 #aac4 ,heinze1 #aci4 ,hellriegel1 #e1 #f1 #df4 ,hensen1 #ajj4 ,hesselmann1 #cf4 ,hill1 #id4 ,hiltner1 #bc4 ,hopkins1 #cf4 ,hutchinson1 ,c4 ,m41 #db4 ,hutchinson1 ,h4 ,b41 #bg1 #dc1 #dg1 #ea1 #eg1 #aje4 ,,van ,,iterson1 #acc4 ,,jensen1 #aah1 #acb4 ,jewson1 #abc4 ,joffe1 #cg4 ,jones1 ,d4 ,h4 and ,murdock1 #abg4 ,jones1 ,l4 ,r41 #adj4 ,,kappen1 #acf4 ,karrer1 #aje4 ,kaserer1 #bg4 ,klcker1 #acd4 ,koch1 ,a41 #dd1 #acd4 ,koch1 ,r41 #bj1 #ec4 ,kofoid1 #hh4 ,kohshi1 #acd4 ,kopeloff1 #aah1 #acf4 ,kossowitsch1 #aaa4 ,krainskii1 #dd4 ,krzeminiewski1 #dc4 ,kufferath1 #ajg4 ,,latham1 #ace4 ,laurent1 #acf4 ,lawes and ,gilbert1 #e4 ,lebedeff1 #bg4 ,leeuwenhoeck1 #bj4 ,lendner1 #aah4 ,lipman1 ,c4 ,b41 #da1 #db1 #dd1 #ed4 ,lipman1 ,j4 ,g41 ,blair1 ,owen1 and ,mc,lean1 #id4 ,lhnis1 #bb1 #dc1 #fi1 #acf4 ,,magnus1 #ajg4 ,malpighi1 #df4 ,marchal1 #cd1 #acf4 ,martin1 #gc4 ,martin and ,lewin1 #fi4 ,mc,beth1 #bh1 #acd4 ,mc,beth and ,scales1 #aah1 #adj4 ,mc,lean and ,wilson1 #aah1 #acf4 ,mockeridge1 #dc4 ,moore1 ,g4 ,t41 #aje4 ,morris1 #aej1 #aea1 #afb4 ,muntz and ,coudon1 #aah1 #acf4 ,,nabokich1 #bg4 ,nagaoka1 #ch4 ,nakano1 #ajg4 ,nasir1 #id1 #ie4 ,neller1 #acg4 ,,omelianski1 #bg1 #db4 ,orla-,jensen1 #bf1 #ce4 ,otto1 #acc4 ,oudemans and ,koning1 #aah4 ,,pasteur1 #c1 #bj4 ,perey1 #id4 ,perotti1 #acf4 ,petersen1 #ajd4 ,pillai1 #dc4 ,potter and ,snyder1 #acg1 #ach4 ,povah1 #ach4 ,pratt1 #acb4 ,prescott1 #fa4 ,pringsheim1 #ajg4 ,,ramann1 #aah4 ,rathbun1 #abj4 ,reh1 #afb4 ,remy1 #aah4 ,richards1 #aab4 ,richardson1 #aei4 ,ritter1 #ach4 ,robbins1 ,w4 ,j41 #aji4 ,robbins1 ,w4 ,w41 #aje4 ,roussy1 #acd4 ,russell1 #aab4 ,russell and ,hutchinson1 #eg1 #ff1 #id4 ,,salunskov1 #db4 ,sandon1 #eg1 #ge4 ,scales1 #bh1 #acd4 ,schellenberg1 #acc4 ,schindler1 #ajg4 ,schloesing1 #c1 #d1 #cd4 ,schmitz1 #acd4 ,schramm1 #aaa4 ,servettaz1 #aji4 ,seydel1 #dd4 ,sherman1 #fi4 ,shibata1 #acf4 ,shngen1 #bf1 #bg1 #acd4 ,,takahashi1 #aah4 ,taylor1 #abj4 ,ternetz1 #ace4 ,treub1 #aab4 ,truffaut1 #fi4 ,,verkade and ,shngen1 #acd4 ,von ,ubisch1 #aji4 ,,waksman1 #cg1 #aah1 #abj1 #aba1 #abc1 #abe1 #abf1 #acd1 #acf4 ,waksman and ,cook1 #acf4 ,wann1 #aaa4 ,warington1 #d1 #cd4 ,waynick1 #db4 ,welwitsch1 #aab4 ,werkenthin1 #abj1 #aba4 ,west1 #hh1 #aje4 ,whiting1 #cf4 ,wilfarth1 #df4 ,winogradsky1 #d1 #f1 #cd1 #da1 #dd4 ,,subject ,,index4 ,absidia1 #aba4 ,acarina1 #aej1 #aea1 #aeg4 ,acid formation by ,fungi1 #aci4 ,acidity of soil1 #ag2 effect on ,actinomyces1 #adj2 relation to nitrification1 #cf4 ,actinomycetes1 #aai1 #acd1 #aci4 ,aeration of soil1 effect on bacteria of1 #fa4 ,agriotes1 #aej4 ,air supply in soil1 #ag4 ,alg1 agents causing disappearance of nitrate from soil1 #ab2 associations of1 in soil1 #aje1 #ajf2 blue green1 #ajb sqq4 7see also ,cyanophyce and ,myxophyce72 colonisation of new ground by1 #aab2 conditions of growth for1 #aja1 #ajd1 #ajg1 #ajh2 distribution of1 #ajb1 #ajd1 #ajf1 #aji2 economic significance of1 #ajj1 #ajb2 filamentous1 #ajf2 flora of soil1 #aja1 #aab2 formation of humus substances1 #aab2 fragmentation of filaments1 #ajg1 #aaj2 frequency of occurrence1 #ajb sqq42 glucose1 effect of1 on growth1 #ajh1 #aji2 green1 #ajd sqq4 7see also ,chlorophyce72 importance in cultivation of rice1 #aac2 numbers in soil of1 #aji1 #aaj2 nutrition of1 #ajg1 #ajh1 #aaj2 producers1 of organic substance1 #ajj2 pure cultures of1 #ajg1 #aaa2 relation to gaseous interchange in soil1 #aac2 relation to soil moisture1 #aab2 seasonal changes in numbers of1 #hh2 subterranean1 #aje4 ,alkaloids1 as source of nitrogen for fungi1 #ach4 ,alternaria1 #aai4 ,amino-acids1 formation of1 by alg1 #ajh4 ,amino-compounds1 decomposition of1 by fungi1 #acf1 #ach4 ,ammonia1 assimilation of1 by bacteria1 #cc1 #dj1 #de2 effect of partial sterilisation on soil content of1 #ff2 formation in soil1 #agj2 formation in soil by bacteria1 #cb sqq42 formation in soil by fungi1 #ace sqq41 #ada2 influence of physical conditions on formation of1 #acg2 property of attracting ,diptera1 #aei2 utilisation by higher plants1 #cf4 ,ammonium sulphate1 effect on fungi1 #aba1 #abf1 #abg4 ,anabna1 #ajb1 #aab4 ,annelida1 #adi4 ,antagonism of salts in soil1 #fj4 ,ants1 #aec4 ,arachnida1 #aej1 #aea4 ,arctic soil1 bacterial flora of1 #bd4 ,areinida1 #aej1 #aea1 #aeg4 ,armillaria1 #acb4 ,ascomycetes1 #aai4 ,aspergillace1 #acf4 ,aspergillus1 #aai1 #abj1 #ace1 #acf1 #ach1 #aci4 ,azotobacter1 #f1 #da1 #ie1 #if2 assimilation of nitrates by1 #de2 decreasing efficiency in liquid culture1 #dd2 indicator of soil acidity1 #dd4 ,,bacillariace1 #ajj 7see also ,diatom74 ,bacillus amylobacter1 distribution of1 #bd4 ,bacillus radicicola1 #bd1 #df sqq42 inoculation of soil with1 #ej2 life cycle of1 #dg4 ,bacteria1 association with alg in nitrogen fixation1 #aaa2 anrobic respiration of1 #cg2 effect of arsenic on1 #fa2 cellulose destroying1 #acd2 changes in morphology in culture1 #bb1 #dg2 classification of main groups1 #bc1 #be2 composition of cells of1 #ci2 inverse relationship with protozoa1 #aj1 #gi1 #hb sqq42 isolation from soil1 #ba2 methods of describing1 #ba2 method of estimating numbers of1 #ec sqq41 #hj2 nitrogen fixation by1 #aaj1 #aaa2 numbers in relation to alg1 #aaj2 numbers in soil1 #eb sqq42 oxidation of hydrogen by1 #bg1 #cg2 effect of partial sterilisation on1 #h1 #i1 #ff1 #fg2 part played in soil fertility by1 #g2 pure cultures1 isolation by plating1 #bj2 seasonal changes in numbers of1 #ei1 #hg sqq42 effect of salts on1 #fj2 short time changes in numbers of1 #aa1 #eg1 #eh2 effect of temperature on1 #fg2 uneven distribution of1 #eg4 ,basidiomycetes1 #aai1 #abc1 #acb4 ,beets1 attacked by ,phoma bet1 #ace4 ,boletus1 #acb4 ,botrytis1 #abb4 ,bryophyta1 #ajj1 #acb4 ,bumilleria1 #aje4 ,,calcium compounds in soil and fungi1 #aci4 ,carabid1 #aej4 ,carbohydrates1 decomposition by bacteria1 #bf sqq42 decomposition by fungi1 #adj2 decomposition in soil1 #afh2 effect on ammonia production in soil1 #cc2 presence in algal sheath and bacteria1 #aaa4 ,carbon1 changes in amount in soil1 #afg2 relationships of bacteria1 #bg2 relationships of fungi1 #acc2 source of1 for soil bacteria1 #ci2 sources of1 for soil fungi1 #aci4 ,carbon dioxide1 assimilation by alg1 #ii1 #ajg1 #ajh2 assimilation by soil bacteria1 #ce1 #cf1 #dj4 ,carotin1 in alg1 #ajj2 formed by ,spirochta cytophaga1 #bi4 ,cecidomyid1 #aee4 ,cellulose1 decomposition by bacteria1 #bg1 sqq42 decomposition by fungi1 #acc1 #acd1 #ada2 relation of nitrogen supply to decomposition of1 #cj2 decomposition in soil1 #afh2 as source of energy for nitrogen fixation1 #dc4 ,centipedes1 see ,chilopoda4 ,cephalosporium1 #abj4 ,cephalothecium1 #acf4 ,chilopoda1 #aeg4 ,chironomid1 #aee4 ,chlorella1 #ajh4 ,chlorococcum1 #aje4 ,chlorophyce1 #ajj4 ,chlorophyll1 loss of1 from alg1 #ajh4 ,ciliates1 classification of1 #gb2 cyst wall of1 #gc4 ,citric acid1 formation of1 by fungi1 #aci4 ,cladosporium1 #aai4 ,clamp connections in fungi1 #aai4 ,classification1 of alg1 #ajj2 of bacteria1 #bc1 #be2 of fungi1 #aca2 of protozoa1 #fi sqq4 ,climate1 effect of1 on alg1 #aja4 ,clostridium1 #da1 #dd2 as fixer of nitrogen1 #f4 ,coccomyxa1 #ajd4 ,coleoptera1 #aej1 #aed1 #aee4 ,collembola1 #aej1 #aec1 #aed4 ,colletotrichum1 #aca4 ,commensals1 #acb4 ,conjugat1 #ajj4 ,cortinarius1 #acb4 ,cotton1 destroyed by fungi1 #acd4 ,counting1 of alg1 #aji2 of bacteria1 #ec sqq42 of fungi1 #abb2 of protozoa1 #gg1 #gi1 #hj4 ,cresol1 decomposition of1 by bacteria1 #bb1 #bd1 #ca4 ,criteria1 physiological1 of fungi1 #abh4 ,crop growth1 effect on fungi1 #abb4 ,cryptomonadine1 #ajj4 ,cucumber leaf spot1 #aca4 ,cyanamide1 decomposition of1 by fungi1 #acf4 ,cyanophyce1 #ajc 7see also ,myxophyce and blue-green alg74 ,cylindrospermum1 #ajb4 ,cysts1 #fh1 #gc1 #gd4 ,,denitrification1 by bacteria1 #cg2 by fungi1 #acf4 ,desiccation1 resistance to1 by alg1 #ajf4 ,dew1 relation to alg1 #aja1 #aac4 ,diatoms1 #ajd sqq4 7see also ,bacillariace74 ,dicyanamide1 decomposition of1 by fungi1 #acf4 ,dipeptides1 formation of1 by alg1 #ajh4 ,diplopoda1 #aeg4 ,diptera1 #aej1 #aed1 #aee1 #aei4 ,disaccharides and fungi1 #acd4 ,,earthworms1 abundance of1 in soil1 #aec2 effect of1 in soil1 #ac1 #afj1 #age4 ,eel-worms1 #adi 7see also ,nematoda74 ,elaphomyces1 #acb4 ,enchytrid1 #adi4 ,energy1 laws of1 #afe2 relationships of soils1 #aff2 requirements of soil organisms1 #ae1 #af4 ,energy supply1 relation of bacterial activities to1 #be sqq41 #dj1 #dd2 sources of1 for soil bacteria1 #bf sqq41 #dj1 #dc2 supplies of1 for soil organisms1 #aaa1 #afd1 #afg1 #afh4 ,environmental conditions in soil1 #af4 ,eremacausis1 #b4 ,ericales1 #acb1 #ace4 ,euglena1 #ii4 ,euglenace1 #ajj4 ,experimental error1 in bacterial counts1 #ed2 in fungal counts1 #abd4 ,,farmyard manure1 see ,manure4 ,fats1 used by fungi1 #acd4 ,fatty acids used by fungi1 #acd4 ,fertility of soil1 views on1 #b2 effect of decomposition of plant residues on1 #a1 #afe2 effect of organisms on1 #age4 ,filter paper1 destruction of1 by fungi1 #acc2 destruction of1 by ,spirochta cytophaga1 #bh4 ,fixation of nitrogen1 discovery of1 by ,berthelot1 #e2 by bacteria1 #dj sqq42 by alg1 #aaj1 #aaa2 by mixtures of bacteria and alg1 #aaa2 by fungi1 #ace sqq4 7see also ,nitrogen ,fixation74 ,flagellat1 #ajj4 ,flax sickness and fungi1 #abb4 ,formaldehyde1 as agent for destroying fungi1 #ada4 ,fungi1 control of1 in soil1 #aci sqq42 counting of1 #abb2 distribution of1 in soil1 #aai sqq41 #abg2 fertilisers1 effect of1 on numbers of in soil1 #abf2 as facultative parasites1 #aca1 #acb2 fruiting bodies of1 #abc2 destruction of hemicelluloses by1 #acc2 individual1 #abb1 #abc2 action on monosaccharides of1 #acd2 mineral relationships of1 #aci2 mycorrhizal1 #acb1 #ace1 #aci1 #adj2 heterocyclic nitrogen compounds and1 #ach2 occurrence in soil1 #aah2 qualitative study of1 #aah2 selective feeding of1 #adj2 specific determination of1 #aai4 ,fungi imperfecti1 #aai4 ,fusaria1 #acd4 ,fusarium1 #aai1 #abj1 #abb1 #abh1 #acc1 #acf4 ,gamascid1 #aef4 ,gases of swamp water 7,paddy soils71 #aac4 ,gastrodia1 #acb4 ,gelatinous envelope of alg1 #aji1 #aaa4 ,geographical distribution of azotobacter1 #da2 of soil bacteria1 #bd2 of protozoa1 #ge1 #gf2 of soil fungi1 #aai1 #abe4 ,germination1 of algal spores1 #ajg4 ,glucose1 use of1 by algae1 #ajh1 #aji1 #aaa2 use of1 by moss protonema1 #aji4 ,glycocoll1 formation of1 by alg1 #ajh4 ,granulobacter1 #db4 ,greenland1 bacteria in soil from1 #bd4 8,grunlandmoor10 fungi in1 #abf4 ,hantzschia1 #aje4 ,hemiptera1 #aed4 ,heterokont1 #ajj4 8,hochmoor10 fungi in1 #abf4 ,hormidium1 #ajd4 ,humus1 the food of plants1 #a2 formation of1 by fungi1 #acd1 #ada2 formation of1 in soil1 #afh2 forest1 #acb2 fungal hyph as constituent of forest humus1 #acb4 ,hydrogen ion concentration1 in soil1 #ag2 effect on fungi of1 #abd4 ,hymenoptera1 #aej1 #aed4 ,insecta1 #aej1 #aeg4 ,insects1 numbers present in soil1 #aed4 ,invertebrata1 definition of1 #adg2 method of investigating1 #adh2 groups represented1 #adi2 distribution in the soil1 #aea2 dominant species and groups1 #aec2 environmental factors of1 #aeg2 feeding habits1 #aef2 relation to agriculture1 #afj2 relation to nitrogen cycle1 #afa4 ,iron compounds1 oxidation by fungi1 #aci4 ,isopoda1 #aej1 #aea4 ,leguminos1 association with bacteria1 #df sqq42 enrichment of ground by1 #e4 ,lepidoptera1 #aej1 #aed4 ,life cycles1 of bacteria1 #bb1 #dg2 of protozoa1 #gb sqq4 ,lime1 effect on fungi in soil1 #aba1 #abf4 ,lyngbya1 #aab4 ,,magnesium compounds1 effect on fungi1 #aci4 ,manganese compounds1 effect on bacteria1 #fa4 ,manure1 farmyard1 effect on alg1 #aji1 #aaj2 effect on numbers of bacteria1 #fj2 effect on numbers of fungi1 #abf2 effect on numbers of insects1 #aed1 #aee4 ,manure1 ,artificial1 effect on fungi1 #abg4 ,manure1 town stable1 occurrence of disease organisms in1 #acb4 ,mastigophora1 classification of1 #ga2 species of1 #ga4 ,media1 containing nitrates1 chemical analysis of1 #aaa2 for counting soil bacteria1 #ed2 for counting protozoa1 #gi2 for counting fungi1 #aai1 #abc4 ,melanconium1 #acd4 ,melolontha1 #aej4 ,methane1 oxidation of1 by bacteria1 #bf1 #bg4 ,millipedes1 see ,diplopoda4 ,mites1 see ,acarina4 ,mollusca1 #adi1 #aeg4 ,moniliace1 #acf4 ,mucor1 #abj1 #aba1 #acf1 #ach4 ,mucorales1 #aba1 #acd4 ,mucorine1 #aah4 ,mycetophilid1 #aee4 ,mycorrhiza1 #acb1 #ace1 #aci1 #adj4 ,myriapoda1 #aej1 #aef4 ,myxophyce1 #ajj 7see also ,cyanophyce and blue-green alg74 ,,naphthalene1 decomposition of1 by bacteria1 #ca4 ,naviculoide1 #ajj4 ,nematoda1 #adi1 #aea1 #aeg4 ,nitrate1 assimilation by alg1 #aje1 #ajh1 #aaa2 assimilation by bacteria1 #cc1 #dj1 #dd1 #ea2 assimilation by fungi1 #acf1 #ach2 removal from soil1 #ab1 #aab1 #aga2 variations in amount in soil1 #aa4 ,nitre-beds1 #a4 ,nitrification1 and bacteria1 #cd2 chemical changes in1 #aga2 and fungi1 #acf2 energy supply in1 #ce2 mechanism of1 #a1 #c2 and soil fertility1 #a1 #c4 ,nitrites and fungi1 #acf2 formation by bacteria1 #cd4 ,nitrobacter1 #ce4 ,nitrogen1 changes in amount in soil1 #afg2 cycle in soil1 #afa2 fixation by bacteria1 #f1 #dj sqq42 fixation by fungi1 #ace1 #acf1 #ada2 fixation of1 in clover plant1 #e2 increase by protozoa of fixation of1 #id1 #ie 7fig472 fixation sources of energy for1 #dc1 #di2 gain of1 in soil1 #agd2 in invertebrates1 #afb2 loss of1 by leaching1 #aab2 loss of1 from cultivated soils1 #agc2 relationships of fungi1 #ace2 relationships of alg1 #aaj-aab2 relationships of bacteria1 #cb sqq41 #dj sqq42 relationships of insects1 #afb4 ,nitrosococcus1 #ce4 ,nitrosomonas1 #ce4 ,nodule ,organism of the ,leguminos1 #f1 #df sqq4 ,nostocace1 #ajj1 #aja1 #ajb1 #ajg4 ,oligochta1 #adi1 #aea1 #aec1 #aeg4 ,oospora1 #abj4 ,orcheomyces1 #acb4 ,orchid cultivation and fungi1 #acb1 #adj4 ,orthoptera1 #aed4 ,oscillatoriace1 #ajj1 #ajb4 ,osmotic pressure1 influencing effect of salts on bacteria1 #ej4 ,oxalic acid1 formation of1 by fungi1 #aci4 ,oxidations effected by soil organisms2 by bacteria1 #bf et seq42 by fungi1 #aci4 ,oxygen1 absorption by soils1 #d4 ,,partial sterilisation of soil1 #h1 #ff sqq41 #if1 #agh2 influence of organic antiseptics1 #agg2 limiting factor in1 #fg1 #fh4 ,pectin1 effect of1 on fungi1 #acd4 ,pedras negras1 #aab4 ,penicillia1 #acd4 ,pentosans1 effect of1 on fungi1 #acd4 ,peptones1 decomposition of1 by fungi1 #acf1 #ach2 source of nitrogen for alg1 #ajh4 ,periodicity1 of protozoa in soil1 #ij sqq4 7fig471 #ib 7fig471 #ic4 ,phenol1 decomposition of1 by bacteria1 #bd1 #be1 #ca4 ,phenylalanine1 formation of1 by alg1 #ajh4 ,phoma1 #acb4 ,phormidium1 #ajf4 ,phosphates1 availability of1 influenced by bacteria1 #eb2 by fungi1 #aci2 effect on bacteria1 #df1 #ea1 #fj4 ,photosynthesis1 #ii1 #ajj1 #ajg1 #aaj1 #aac4 ,phycocyanin1 #ajj4 ,physical conditions in soil1 #af4 ,physiological criteria1 of bacteria1 #bb2 of fungi1 #abh4 ,phycomycetes1 #aai4 ,phytophthora1 #acb4 ,plant disease1 and fungi1 #aci4 ,plant residues1 decomposition of1 in soil1 #afh2 influence of soil reaction on1 #afe2 relation to soil fertility1 #a1 #afe4 ,plasticity of fungi1 #aai4 ,plectonema1 #ajf4 ,potassium salts1 effect on bacteria1 #fj2 influence of bacteria on the availability of1 #eb4 ,protein1 decomposition of1 in soil1 #afi2 decomposition by bacteria1 #cb2 decomposition by fungi1 #ach1 #adj4 ,protococcales1 #ajj4 ,protoderma viride1 #aje4 ,protonema of mosses1 #ajj1 #aje1 #ajf1 #aji4 ,protophyta1 chlorophyll-bearing1 #ajj4 ,protozoa1 inoculation into soil of1 #he sqq42 isolation from soil1 #fi2 classification of1 #fi sqq42 life histories of1 #gb sqq42 species of1 in soil1 #gj sqq42 distribution of1 in soil1 #gd sqq42 retention of1 by soil1 #gh 7fig472 size of1 #ij2 reproductive rates1 #ic2 inverse relation with bacteria1 #gi sqq42 presence of trophic forms in soil1 #i2 numbers of1 in soil1 #ij1 #if1 #ig2 fluctuations in numbers of1 #aj1 #ha 7fig471 #hb2 external conditions1 effect on1 #hb2 seasonal changes1 effect on1 #hg sqq42 weight of1 #ij4 ,pteridophyta1 #acb4 ,pythium1 #acb4 ,,reaction of soil1 #ag4 ,reaction of soil1 effect on bacteria1 #cf1 #cg1 #df1 #dh1 #fa2 effect on protozoa1 #ic1 #id 7see also hydrogen ion concentration74 ,relationships of ,fungi1 commensal1 #acb2 mycorrhizal1 #acb2 symbiotic1 #acb4 ,rhizopoda2 classification of1 #gj1 #ga2 species of1 #gj1 #ga4 ,rhythm1 supposed in ammonification by fungi1 #acg4 ,rhizoctonia1 #acb4 ,rhizopus1 #aai1 #abj4 ,rice plant1 aeration of roots1 #aac2 physiological disease of1 #aac4 ,rock ,phosphate as base for nitrifying organisms1 #cf4 ,rothamsted1 ,broadbalk plot #b 7,farmyard ,manure7 alg1 #aji2 fungi1 #abe1 #abg2 ,insects1 #aeb4 ,rothamsted1 ,broadbalk plot #c 7,unmanured7 alg1 #aji2 fungi1 #abj1 #abb1 #abg2 ,insects1 #aeb4 ,rothamsted1 ,broadbalk ,plots #aj1 #aa1 and #ac2 #abb1 #abg4 ,rothamsted1 ,barnfield ,plot #a-j 7,farmyard ,manure71 ,protozoa1 #hj4 ,rothamsted1 unmanured grass plot1 #abj4 ,russula1 #acb4 ,rusts1 #aai4 ,saccharomyces1 #abj4 ,saprophytes1 facultative1 #aca4 ,saprophytism and alg1 #ajh1 #aaj4 ,scenedesmus1 #ajh4 ,seasonal fluctuations in numbers of soil organisms1 #ab1 #hg et seq41 #abe4 ,selective media1 use of1 in isolation of soil bacteria1 #ba4 ,serological tests1 separation of varieties of ,b4 radicicola by1 #dh4 ,slugs1 see ,mollusca4 ,smuts1 #aai4 ,snails1 see ,mollusca4 ,soil2 comparison of1 by volume1 #ag2 effect of depth below surface on alg1 #aja1 #ajd1 #aji1 #aaj1 #aac2 effect of depth below surface on insects1 #aea2 effect of depth below surface on fungi1 #aba1 #abf1 #abg2 effect of various treatments on fungi1 #abf1 #abg1 #acb2 environmental factors in1 #af2 inoculation of1 for leguminous plants1 #ej2 moisture 7see ,water supply72 population1 control of1 #agg sqq42 population1 methods of investigation1 #aj1 #ae2 sterilisation and fungi1 #acg1 #ach1 #ada 7see ,partial ,sterilisation72 stored1 survival of alg in1 #ajg2 type and fungi1 #aba1 #abf1 #abg4 ,soil conditions1 effect on bacteria1 #cc1 #cf1 #cg1 #dj1 #df1 #dh1 #ej1 #ei sqq42 effect on protozoa1 #hb4 ,soil fertility1 see ,fertility of soil4 ,spicaria1 #abj4 ,spiders1 see ,areinida4 ,spirochta cytophaga1 #bh1 #dc4 ,spore forming bacteria in soil1 #bc1 #cd4 ,spore1 fungus1 inhibition of formation1 #abc2 presence in air of1 #aah4 ,standardisation of cultural methods for soil bacteria1 #ed sqq4 ,starch1 decomposition of1 by fungi1 #acd4 ,stichococcus1 #ajh4 ,straw2 effect on nitrate production in soil1 #cc2 manure1 #bi2 rotting of1 #cj4 ,sulphur oxidation1 by bacteria1 #cg2 by fungi1 #aci4 ,symbiosis1 of ,azotobacter with other organisms1 #db1 #dc1 see also ,mycorrhiza and ,nodule organism4 ,symphyla1 #aej1 #aea1 #aeg4 ,symploca1 #aab4 ,tachinid1 #aej4 ,tannins1 used by fungi1 #acd4 ,temperature of soil and fungi1 #abg1 #adj4 ,termites1 #afj4 ,testacella1 #adi4 ,thiospirillum1 #cg4 ,thysanura1 #aed4 ,thysanoptera1 #aed4 ,tipula1 #aej4 ,toluene1 decomposition by soil bacteria1 #ca4 ,tolypothrix1 #aab4 ,trichoderma1 #aai1 #abj1 #abb1 #acd4 ,trochiscia1 #aje4 ,tropisms1 #aeg4 ,ulothrix1 #aje4 ,ulotrichales1 #ajj4 ,urea1 by fungi1 #acf1 #ach4 ,uric acid1 utilisation of1 by fungi1 #ach4 ,vaucheria1 #ajd1 #ajf4 ,vitality1 retention of1 by alg and moss protonema1 #aje1 #ajg4 ,,water2 supply in soil1 #ag2 and alg1 #aab2 bacteria1 #ej1 #fa1 #hb2 fungi1 #abg2 protozoa1 #hb4 ,wireworms1 #aee4 ,wood1 decay of1 #acd4 ,woodlice1 #aej2 7see also ,isopoda74 ,,yeasts1 #ach4 ,zygnema1 #ajd4 ,zygorrhynchus mlleri1 #aai1 #abj1 #aba4 ,,printed ,,in ,,great ,,britain ,,by ,,the ,,university ,,press1 ,,aberdeen ,transcriber's ,notes ,inconsistent and archaic or unusual spelling1 capitalisation1 italicisation1 hyphenation1 etc4 have been retained1 unless mentioned below4 ,the names and classifications of the organisms as used in the book do not always conform to modern names and classifications2 these have not been changed4 ,depending on the hard- and software used and their settings1 not all elements may display as intended4 ,page #ad1 table1 lower right hand cell3 the data given add up to #h1 not to #i4 ,page #dg1 #i #ah in size3 the source document does not include the units2 presumably the sizes are in microns4 ,page #aah1 endnote #h;c 7#b73 this note does not exist4 ,subject ,index1 entry ,zygorrhynchus mlleri3 also refers to ,zygorrhynchus vuilleminii4 ,changes made3 ,footnotes1 tables and illustrations have been moved out of text paragraphs2 some tables have been split or re-arranged4 ,several minor obvious typographical1 punctuation and spelling errors 7including accents7 have been corrected silently4 ,in several cases spelling differences 7mainly of proper names7 between the text and the index and endnotes have been standardised4 ,in the indexes and in tables some ditto marks have been replaced with the dittoed text4 ,some page references have been corrected to indicate the correct page number4 ,indented text under illustrations is not present as such in the source document1 but has been transcribed from the illustration for legibility and ease of reference4 ,some tables have been re-arranged or split to fit the available width4 ,page #bh1 #bi3 ,mac,beth changed to ,mc,beth as elsewhere 7in the ,author ,index the entries ,mac,beth and ,mc,beth have been merged74 ,page #cb1 formula3 #cj changed to #c,o4 ,page #eh3 ,from ,barnfeild1 444 changed to ,from ,barnfield1 4444 ,page #he3 closing bracket deleted after 444 ,table ,,vii4 and ,fig4 #ac4 ,page #ij1 ,table ,,viii1 column #e3 #cejjjj and #aejjjj changed to #cej1jjj and #aej1jjj4 ,page #ig3 ,no creature lies or dies to itself1 444 changed to ,no creature lives or dies to itself1 444 ,page #ajd3 ,danske ,aerofile ,alghe changed to ,danske ,arofile ,alger4 ,page #aad3 ,recherche sulla ,malattia del ,riso 444 changed to ,ricerche sulla ,malattia del ,riso 4444 ,page #aae3 444 sur de polymorphisme 444 changed to 444 sur le polymorphisme 4444 ,page #aaf3 literature notes #ch 7,robbins7 and #dh 7,schindler7 changed to #cc and #cd respectively4 ,page #abj3 ,zygorrhynchus vuillemini changed to ,zygorrhynchus vuilleminii as elsewhere4 ,page #abf3 references to ,waksman#bd and #bd;e changed to #be and #be;e4 ,page #abi3 444 prepare de la pres de ,russum 444 changed to 444 prpare de la terre humeuse du ,spanderswoud1 prs de ,bussum 4444 ,page #acd3 reference to ,kohshi#bd changed to #cd4 ,page #adc3 ,smenbildung changed to ,surenbildung 7entry #e72 ,wurzelbranderregern im ,baden changed to ,wurzelbranderregern im ,boden 7entry #aa74 ,page #add3 444 ,umwandlung von ,aminosamen in ,oxysmen 444 changed to 444 ,umwandlung von ,aminosuren in ,oxysuren 44442 444 ,wirkungen der ,schimmelze 444 changed to 444 ,wirkungen der ,schimmelpilze 44442 ,hydrogen-iron concentration changed to ,hydrogen-ion concentration4 ,page #ade3 ,ztschr4 f4 ,garungs4 ,physiol4 changed to ,ztschr4 f4 ,grungsphysiol4 ,page #adf3 einige ,pilze gegen ,hemizellulosen changed to einiger ,pilze gegen ,hemicellulosen4 ,page #aeg3 ,such responses are known chemotropism 444 changed to ,such responses are known as chemotropism 4444 ,page #agj3 444 alphatic amino-acids 444 changed to 444 aliphatic amino-acids 4444