,,ancient ,,plants ,illustration3 ,photo4 of the specimen in ,manchester ,museum4 ,,the ,,stump ,,of ,a ,,lepidodendron ,,from ,,the ,,coal ,,measures ,,ancient ,,plants ,,being ,a ,,simple ,,account ,,of ,,the ,,past ,,vegetation ,,of ,,the ,,earth ,,and ,,of ,,the ,,recent ,,important ,,discoveries ,,made ,,in ,,this ,,realm ,,of ,,nature ,,study ,,by ,,marie ,c4 ,,stopes1 ,d4,sc41 ,ph4,d41 ,f4,l4,s4 ,lecturer in ,fossil ,botany1 ,manchester ,university ,author of 8,the ,study of ,plant ,life for ,young ,people0 ,,london ,,blackie ,,son1 ,limited1 #ej ,,old ,,bailey1 ,e4,c4 ,,glasgow ,,and ,,bombay #aiaj ,preface ,the number and the importance of the discoveries which have been made in the course of the last five or six years in the realm of ,fossil ,botany have largely altered the aspect of the subject and greatly widened its horizon4 ,until comparatively recent times the rather narrow outlook and the technical difficulties of the study made it one which could only be appreciated by specialists4 ,this has been gradually changed1 owing to the detailed anatomical work which it was found possible to do on the carboniferous plants1 and which proved to be of great botanical importance4 ,about ten years ago textbooks in ,english were written1 and the subject was included in the work of the honours students of ,botany at the ,universities4 ,to-day the important bearing of the results of this branch of ,science on several others1 as well as its intrinsic value1 is so much greater1 that anyone who is at all acquainted with general science1 and more particularly with ,botany and ,geology1 must find much to interest him in it4 ,there is no book in the ,english language which places this really attractive subject before the non-specialist1 and to do so is the aim of the present volume4 ,the two excellent ,english books which we possess1 viz4 ,seward's ,fossil ,plants 7of which the first volume only has appeared1 and that ten years ago7 and ,scott's ,studies in ,fossil ,botany1 are ideal for advanced ,university students4 ,but they are written for students who are supposed to have a previous knowledge of technical botany1 and prove very hard or impossible reading for those who are merely acquainted with ,science in a general way1 or for less advanced students4 ,the inclusion of fossil types in the ,south ,kensington syllabus for ,botany indicates the increasing importance attached to palobotany1 and as vital facts about several of those types are not to be found in a simply written book1 the students preparing for the examination must find some difficulty in getting their information4 ,furthermore1 ,scott's book1 the only up-to-date one1 does not give a complete survey of the subject1 but just selects the more important families to describe in detail4 ,hence the present book was attempted for the double purpose of presenting the most interesting discoveries and general conclusions of recent years1 and bringing together the subject as a whole4 ,the mass of information which has been collected about fossil plants is now enormous1 and the greatest difficulty in writing this little book has been the necessity of eliminating much that is of great interest4 ,the author awaits with fear and trembling the criticisms of specialists1 who will probably find that many things considered by them as particularly interesting or essential have been left out4 ,it is hoped that they will bear in mind the scope and aim of the book4 ,i try to present only the structure raised on the foundation of the accumulated details of specialists' work1 and not to demonstrate brick by brick the exposed foundation4 ,though the book is not written specially for them1 it is probable that ,university students may find it useful as a general survey of the whole subject1 for there is much in it that can only be learned otherwise by reference to innumerable original monographs4 ,in writing this book all possible sources of information have been consulted1 and though ,scott's ,studies#a naturally formed the foundation of some of the chapters on ,pteridophytes1 the authorities for all the general part and the recent discoveries are the numerous memoirs published by many different learned societies here and abroad4 ,as these pages are primarily for the use of those who have no very technical preliminary training1 the simplest language possible which is consistent with a concise style has always been adopted4 ,the necessary technical terms are either explained in the context or in the glossary at the end of the book4 ,the list of the more important authorities makes no pretence of including all the references that might be consulted with advantage1 but merely indicates the more important volumes and papers which anyone should read who wishes to follow up the subject4 ,all the illustrations are made for the book itself1 and ,i am much obliged to ,mr4 ,d4 ,m4 ,s4 ,watson1 ,b4,sc41 for the microphotos of plant anatomy which adorn its pages4 ,the figures and diagram are my own work4 ,this book is dedicated to college students1 to the senior pupils of good schools where the subject is beginning to find a place in the higher courses of ,botany1 but especially to all those who take an interest in plant evolution because it forms a thread in the web of life whose design they wish to trace4 ,m4 ,c4 ,,stopes4 ,december1 #aiji4 ,contents ,chap4 ,page ,i4 ,introductory #a ,,ii4 ,various ,kinds of ,fossil ,plants #f ,,iii4 ,coal1 the most ,important of ,plant ,remains #bb ,,iv4 ,the ,seven ,ages of ,plant ,life #cc ,v4 ,stages in ,plant ,evolution #dc ,,vi4 ,minute ,structure of ,fossil ,plants-- ,likenesses to ,living ,ones #ec ,,vii4 ,differences from ,living ,ones #fi ,,viii4 ,past ,histories of ,plant ,families-- 7i7 ,flowering ,plants #gi ,,ix4 7ii7 ,higher ,gymnosperms #hf ,x4 7iii7 ,bennettitales #ajb ,,xi4 7iv7 ,the ,cycads #aji ,,xii4 7v7 ,pteridosperms #aad ,,xiii4 7vi7 ,the ,ferns #abd ,,xiv4 7vii7 ,the ,lycopods #acc ,,xv4 7viii7 ,the ,horsetails #ade ,,xvi4 7ix7 ,sphenophyllales #aec ,,xvii4 7x7 ,the ,lower ,plants #afa ,,xviii4 ,fossil ,plants as ,records of ,ancient ,countries #afh ,,xix4 ,conclusion #agd ,,appendix ,i4 ,list of ,requirements for a ,collecting ,expedition #ahc ,,ii4 ,treatment of ,specimens #ahd ,,iii4 ,literature #ahf ,glossary #ahh ,footnotes #aic ,index #aic ,,ancient ,,plants ,,chapter ,i ,,introductory ,the lore of the plants which have successively clothed this ancient earth during the thousands of centuries before men appeared is generally ignored or tossed on one side with a contemptuous comment on the dullness and 8dryness0 of fossil botany4 ,it is true that all that remains of the once luxuriant vegetation are fragments preserved in stone1 fragments which often show little of beauty or value to the untrained eye2 but nevertheless these fragments can tell a story of great interest when once we have the clue to their meaning4 ,the plants which lived when the world was young were not the same as those which live to-day1 yet they filled much the same place in the economy of nature1 and were as vitally important to the animals then depending on them as are the plants which are now indispensable to man4 ,to-day the life of the modern plants interests many people1 and even philosophers have examined the structure of their bodies and have pondered over the great unanswered questions of the cause and the course of their evolution4 ,but all the plants which are now alive are the descendants of those which lived a few years ago1 and those again came down through generation after generation from the plants which inhabited the world before the races of men existed4 ,if1 therefore1 we wish to know and understand the vegetation living to-day we must look into the past histories of the families of plants1 and there is no way to do this at once so simple and so direct 7in theory7 as to examine the remains of the plants which actually lived in that past4 ,yet when we come to do this practically we encounter many difficulties1 which have discouraged all but enthusiasts from attempting the study hitherto1 but which in reality need not dismay us4 ,when ,lindley and ,hutton1 in #ahca1 began to publish their classical book ,the ,fossil ,flora of ,great ,britain1 they could give but isolated fragments of information concerning the fossils they described1 and the results of their work threw but little light on the theoretical problems of morphology and classification of living plants4 ,since then great advance has been made1 and now the sum of our knowledge of the subject1 though far from complete1 is so considerable and has such a far-reaching influence that it is becoming the chief inspiration of several branches of modern botany4 ,of the many workers who have contributed to this stock of knowledge the foremost1 as he was the pioneer in the investigations on modern lines1 is ,williamson1 who was a professor at ,manchester ,university1 and whose monographs and specimens are classics to-day4 ,still living is ,dr4 ,scott1 whose greatness is scarcely less1 as well as an ever-increasing number of specialists in this country1 who are continually making discoveries4 ,abroad1 the chief ,continental names are ,renault1 ,bertrand1 ,count ,solms ,laubach1 ,brongniart1 ,zeiller2 and in ,america is ,dr4 ,wieland2 while there are innumerable other workers in the field who have deepened and widened the channels of information4 ,the literature on fossil plants is now vast2 so great that to give merely the names of the publications would fill a very large volume4 ,but1 like the records left by the plants themselves1 most of this literature is unreadable by any but specialists1 and its really vital interest is enclosed in a petrifying medium of technicalities4 ,it is to give their results in a more accessible form that the present volume has been written4 ,the actual plants that lived and died long ago have left either no trace of their form and character1 or but imperfect fragments of some of their parts embedded in hard rock and often hidden deep in the earth4 ,that such difficulties lie in our way should not discourage us from attempting to learn all the fossils can teach4 ,many an old manuscript which is torn and partly destroyed bears a record1 the fragments of which are more interesting and important than a tale told by a complete new book4 ,the very difficulty of the subject of fossil botany is in itself an incentive to study1 and the obstacles to be surmounted before a view of the ancient plants can be seen increase the fascination of the journey4 ,the world of to-day has been nearly explored2 but the world1 or rather the innumerable world-phases of the past1 lie before us practically unknown1 bewilderingly enticing in their mystery4 ,these untrodden regions are revealed to us only by the fossils lying scattered through the rocks at our feet1 which give us the clues to guide us along an adventurous path4 ,fables of flying dragons and wondrous sea monsters have been shown by the students of animal fossils to be no more marvellous than were the actual creatures which once inhabited the globe2 and among the plants such wonderful monsters have their parallels in the floras of the past4 ,the trees which are living to-day are very recent in comparison with the ancestors of the families of lowlier plants1 and most of the modern forest trees have usurped a position which once belonged to the monster members of such families as the ,lycopods and ,equisetums1 which are now humble and dwindling4 ,an ancient giant of the past is seen in the frontispiece1 and the great girth of its stem offers a striking contrast to the feeble trailing branches of its living relatives1 the ,club-mosses4 ,as we follow their histories we shall see how family after family has risen to dominate the forest1 and has in its turn given place to a succeeding group4 ,some of the families that flourished long since have living descendants of dwarfed and puny growth1 others have died out completely1 so that their very existence would have been unsuspected had it not been revealed by their broken fragments entombed in the rocks4 ,from the study of the fossils1 also1 we can discover something of the course of the evolution of the different parts of the plant body1 from the changes it has passed through in the countless ages of its existence4 ,just as the dominant animals of the past had bodies lacking in many of the characters which are most important to the living animals1 so did the early plants differ from those around us to-day4 ,it is the comparative study of living and fossil structures which throws the strongest light on the facts and factors of evolution4 ,when the study of fossil organisms goes into minute detail and embraces the fine subtleties of their internal structure1 then the student of fossil plants has the advantage of the zoological observer1 for in many of the fossil plants the cells themselves are petrified with a perfection that no fossil animal tissues have yet been found to approach4 ,under the microscope the most delicate of plant cells1 the patterns on their walls1 and sometimes even their nuclei can be recognized as clearly as if they were living tissues4 ,the value of this is immense1 because the external appearance of leaves and stems is often very deceptive1 and only when both external appearance and internal structure are known can a real estimate of the character of the plant be made4 ,in the following chapters a number of photographs taken through the microscope will show some of the cell structure from fossil plants4 ,such figures as fig4 #aa and fig4 #if1 for example1 illustrate the excellence of preservation which is often found in petrified plant tissues4 ,indeed1 the microscope becomes an essential part of the equipment of a fossil botanist2 as it is to a student of living plants4 ,but for those who are not intending to specialize on the subject micro-photographs will illustrate sufficient detail1 while in most modern museums some excellently preserved specimens are exhibited which show their structure if examined with a magnifying glass4 ,we recognize to-day the effect the vegetation of a district has on its scenery1 even on its more fundamental nature2 and we see how the plants keep in close harmony with the lands and waters1 the climates and soils of the places they inhabit4 ,so was it in the past4 ,hence the fossil plants of a district will throw much light on its physical characters during the epoch when they were living1 and from their evidence it is possible to build up a picture of the conditions of a region during the epochs of its unwritten history4 ,from every point of view a student of living plants will find his knowledge and understanding of them greatly increased by a study of the fossils4 ,not only to the botanist is the subject of value1 the geologist is equally concerned with it1 though from a slightly different viewpoint1 and all students of the past history of the earth will gain from it a wider knowledge of their specialty4 ,to all observers of life1 to all philosophers1 the whole history of plants1 which only approaches completion when the fossils are studied1 and compared or contrasted with living forms1 affords a wonderful illustration of the laws of evolution on which are based most of the modern conceptions of life4 ,even to those whose profession necessitates purely practical lines of thought1 fossil botany has something to teach2 the study of coal1 for instance1 comes within its boundaries4 ,while to all who think on the world at all1 the story told by the fossil plants is a chapter in the ,book of ,life which is as well worth reading as any in that mystical volume4 ,,chapter ,,ii ,,various ,,kinds ,,of ,,fossil ,,plants ,of the rocks which form the solid earth of to-day1 a very large proportion have been built up from the deposits at the bottom of ancient oceans and lakes4 ,the earth is very old1 and in the course of its history dry land and sea1 mountains and valleys have been formed and again destroyed on the same spot1 and it is from the silt at the bottom of an ocean that the hills of the future are built4 ,the chief key we have to the processes that were in operation in the past is the course of events passing under our eyes to-day4 ,hence1 if we would understand the formation of the rocks in the ancient seas1 we must go to the shores of the modern ones and see what is taking place there4 ,one of the most noticeable characters of a shore is the line of flotsam that is left by the edge of the waves2 here you may find all kinds of land plants mixed with the sea shells and general rubbish1 plants that may have drifted far4 ,much of the dbris 7outside towns7 is brought down by the rivers1 and may be carried some distance out to sea2 then part becomes waterlogged and sinks1 and part floats in to shore1 perhaps to be carried out again1 or to be buried under the coarse sand of the beach4 ,when we examine sandstone rock1 or the finer grained stones which are hardened mud1 we find in them the remains of shells1 sometimes of bones1 and also of plant leaves and stems1 which in their time had formed the flotsam of a shore4 ,indeed1 one may say that nearly every rock which has not been formed in ancient volcanoes1 or been altered by their heat1 carries in it some trace of plant or animal4 ,these remains are often very fragmentary and difficult to recognize1 but sometimes they are wellnigh as perfect as dried specimens of living things4 ,when they are recognizable as plant or animal remains they are commonly called 8fossils01 and it is from their testimony that we must learn all we can know about the life of the past4 ,illustration3 ,fig4 #a4--,the ,face of a ,quarry1 showing layers or 8beds0 of different rock1 a1 b1 and c4 ,the top gravel and soil s has been disintegrated by the growing plants and atmosphere4 ,if we would find such stones for ourselves1 the quarries offer the best hunting ground1 for there several layers of rock are exposed1 and we can reach fresh surfaces which have not been decayed by rain and storm4 ,fig4 #a shows a diagram of a quarry1 and illustrates the almost universal fact that the beds of rock when undisturbed lie parallel to each other4 ,rock a in the figure is fine-grained limestone1 b black friable shale mixed with sand1 and c purer shale4 ,in such a series of rocks the best fossils will be found in the limestone2 its harder and finer structure acting as a better preservative of organisms than the others4 ,in limestone one finds both plant and animal fossils1 very often mixed together as the flotsam on the shore is mixed4 ,many limestones split along parallel planes1 and may break into quite thin sheets on whose surfaces the flattened fossils show particularly well4 ,it is1 however1 with the plant fossils that we must concern ourselves1 and among them we find great variety of form4 ,some are more or less complete1 and give an immediate idea of the size and appearance of the plant to which they had belonged2 but such are rare4 ,one of the best-known examples of this type is the base of a great tree trunk illustrated in the frontispiece4 ,with such a fossil there is no shadow of doubt that it is part of a giant tree1 and its spreading roots running so far horizontally along the ground suggest the picture of a large crown of branches4 ,most fossils1 however1 are much less illuminating1 and it is usually only by the careful piecing together of fragments that we can obtain a mental picture of a fossil plant4 ,a fossil such as that illustrated in the frontispiece--and on a smaller scale this type of preservation is one of the commonest--does not actually consist of the plant body itself4 ,although from the outside it looks as though it were a stem base covered with bark1 the whole of the inner portion is composed of fine hard rock with no trace of woody tissue4 ,in such specimens we have the shape1 size1 and form of the plant preserved1 but none of its actual structure or cells4 ,it is1 in fact1 a ,cast4 ,fossil casts appear to have been formed by fine sand or mud silting round a submerged stump and enclosing it as completely as if it had been set in plaster of ,paris2 then the wood and soft tissue decayed and the hollow was filled up with more fine silt2 gradually all the bark also decayed and the mud hardened into stone4 ,thus the stone mould round the outside of the plant enclosed a stone casting4 ,when1 after lying for ages undisturbed1 these fossils are unearthed1 they are so hard and 8set0 that the surrounding stone peels away from the inner part1 just as a plaster cast comes away from an object and retains its shape4 ,there are many varieties of casts among fossil plants4 ,sometimes on breaking a rock it will split so as to show the perfect form of the surface of a stem1 while its reverse is left on the stone as is shown in fig4 #b4 ,had we only the reverse we should still have been able to see the form of the leaf bases by taking a wax impression from it2 although there is nothing of the actual tissue of the plant in such a fossil4 ,sometimes casts of leaf bases show the detail preserved with wonderful sharpness1 as in fig4 #c4 ,this is an illustration of the leaf scars of ,lepidodendron1 which often form particularly good casts4 ,illustration3 ,fig4 #b4--;,a1 ,cast of the ,surface showing the ,shape of ,leaf ,bases of ,sigillaria2 ,b1 the reverse of the impression left on the adjacent layer of rock4 7,photo47 ,in other instances the cast may simply represent the internal hollows of the plant4 ,this happens most commonly in the case of stems which contained soft pith cells which quickly decayed1 or with naturally hollow stems like the ,horse-tails 7,equisetum7 of to-day4 ,fine mud or sand silted into such hollows completely filling them up1 and then1 whether the rest of the plant were preserved or not1 the shape of the inside of the stem remains as a solid stone4 ,where this has happened1 and the outer part of the plant has decayed so as to leave no trace1 the solid plug of stone from the centre may look very much like an actual stem itself1 as it is cylindrical and may have surface markings like those on the outsides of stems4 ,some of the casts of this type were for long a puzzle to the older fossil botanists1 particularly that illustrated in fig4 #d1 where the whole looks like a pile of discs4 ,illustration3 ,fig4 #c4--;,cast of the ,leaf ,bases of ,lepidodendron1 showing finely marked detail4 7,photo47 ,illustration3 ,fig4 #d4--8,sternbergia40 ,internal cast of the stem of ,cordaites4 ,the true nature of this fossil was recognized when casts of the plan were found with some of the wood preserved outside the castings2 and it was then known that the plant had a hollow pith1 with transverse bands of tissue across it at intervals which caused the curious constrictions in the cast4 ,illustration3 ,fig4 #e4--,leaf ,impressions of 8,fern0 ,sphenopteris on ,shale4 7,photo47 ,another form of cast which is common in some rocks is that of seeds4 ,as a rule these casts are not connected with any actually preserved tissue1 but they show the external form1 or the form of the stony part of the seed4 ,well-known seeds of this type are those of ,trigonocarpon1 which has three characteristic ridges down the stone4 ,sometimes in the fine sandstone in which they occur embedded1 the internal cast lies embedded in the external cast1 and between them there is a slight space1 now empty1 but which once contained the actual shell of the seed1 now decayed4 ,thus we may rattle the 8stone0 of a fossil fruit as we do the dried nuts of to-day--the external resemblance between the living and the fossil is very striking1 but of the actual tissues of the fossil seed nothing is left4 ,casts have been of great service to the fossil botanists1 for they often give clear indications of the external appearance of the parts they represent2 particularly of stems1 leaf scars1 and large seeds4 ,but all such fossils are very imperfect records of the past plants1 for none of the actual plant tissues1 no minute anatomy or cell structure1 is preserved in that way4 ,a type of fossil which often shows more detail1 and which usually retains something of the actual tissues of the plant1 is that known technically as the ,impression4 ,these fossils are the most attractive of all the many kinds we have scattered through the rocks1 for they often show with marvellous perfection the most delicate and beautiful fern leaves1 such as in fig4 #e4 ,here the plant shows up as a black silhouette against the grey stone1 and the very veins of the midrib and leaves are quite visible4 ,fig4 #f shows another fernlike leaf in an impression1 not quite flat like that shown in fig4 #e1 but with a slight natural curvature of the leaves similar to what would have been their form in life4 ,though an impression1 this specimen is not of the 8pressed plant0 type1 it almost might be described as a bas-relief4 ,sometimes impressions of fern foliage are very large1 and show highly branched and complex leaves like those of tree ferns1 and they may cover large sheets of stone4 ,they are particularly common in the fine shales above coal seams1 and are best seen in the mines1 for they are often too big to bring to the surface complete4 ,in most impressions the black colour is due to a film of carbon which represents the partly decomposed tissues of the plant4 ,sometimes this film is cohesive enough to be detached from the stone without damage4 ,beautiful specimens of this kind are to be seen in the ,royal ,scottish ,museum1 ,edinburgh where the coiled bud of a young fern leaf has been separated from the rock on which it was pressed1 and mounted on glass4 ,such specimens might be called mummy plants1 for they are the actual plant material1 but so decayed and withered that the internal cells are no longer intact4 ,in really well preserved ones it is sometimes possible to peel off the plant film1 and then treat it with strong chemical agents to clear the black carbon atoms away1 and mount it for microscopic examination1 when the actual outline of the epidermis cells can be seen4 ,illustration3 ,fig4 #f4--;,impression of ,neuropteris ,leaf1 showing details of veins1 the leaves in partial relief4 7,photo47 ,illustration3 ,fig4 #g4--,leaf ,impression of ,ginkgo1 of which the film was strong enough to peel off complete ,in fig4 #g1 the impression is that of a ,ginkgo leaf1 and after treatment the cells of the epidermis were perfectly recognizable under the microscope1 with the stomates 7breathing pores7 also well preserved4 ,this is shown in fig4 #h1 where the outline of the cells was drawn from the microscope4 ,in such specimens1 however1 it is only the outer skin which is preserved1 the inner soft tissue1 the vital anatomy of the plant1 is crushed and carbonized4 ,leaves1 stems1 roots1 even flowers 7in the more recent rocks7 and seeds may all be preserved as impressions2 and very often those from the more recently formed rocks are so sharply defined and perfect that they seem to be actual dried leaves laid on the stone4 ,illustration3 ,fig4 #h4--,outline of the ,cells from ,specimen of ,leaf shown in fig4 #g c1 ,ordinary cells2 s1 stomates2 v1 elongated cells above the vein4 ,much evidence has been accumulated that goes to show that the rocks which contain the best impressions were originally deposited under tranquil conditions in water4 ,it might have been in a pool or quiet lake with overshadowing trees1 or a landlocked inlet of the sea where silt quietly accumulated1 and as the plant fragments fell or drifted into the spot they were covered by fine-grained mud without disturbance4 ,in the case of those which are very well preserved this must have taken place with considerable rapidity1 so that they were shut away from contact with the air and from the decay which it induces4 ,impressions in the thin sheets of fine rock may be compared to dried specimens pressed between sheets of blotting paper2 they are flattened1 preserved from decay1 and their detailed outline is retained4 ,fossils of this kind are most valuable1 for they give a clear picture of the form of the foliage1 and when1 as sometimes happens1 large masses of leaves1 or branches with several leaves attached to them1 are preserved together1 it is possible to reconstruct the plant from them4 ,it is chiefly from such impressions that the inspiration is drawn for those semi-imaginary pictures of the forests of long ago4 ,from them also are drawn many facts of prime importance to scientists about the nature and appearance of plants1 of which the internal anatomy is known from other specimens1 and also about the connection of various parts with each other4 ,sometimes isolated impressions are found in clay balls or nodules4 ,when the latter are split open they may show as a centre or nucleus a leaf or cone1 round which the nodule has collected4 ,in such cases the plant is often preserved without compression1 and may show something of the minute details of organization4 ,the preservation1 however1 is generally far from perfect when viewed from a microscopical standpoint4 ,fig4 #i shows one of these smooth1 clayey nodules split open1 and within it the cone which formed its centre1 also split into two1 and standing in high relief1 with its scales showing clearly4 ,similar nodules or balls of clay are found to-day1 forming in slowly running water1 and it may be generally observed that they collect round some rubbish1 shell1 or plant fragment4 ,these nodules are particularly well seen nowadays in the mouth of the ,clyde1 where they are formed with great rapidity4 ,illustration3 ,fig4 #i4--;,clay ,nodule split open1 showing the two halves of the cone which was its centre4 7,photo47 ,another kind of preservation is that which coats over the whole plant surface with mineral matter1 which hardens1 and thus preserves the form of the plant4 ,this process can be observed going on to-day in the neighbourhood of hot volcanic streams where the water is heavily charged with minerals4 ,in most cases such fossils have proved of little importance to science1 though there are some interesting specimens in the ,french museums which have not yet been fully examined4 ,a noteworthy fossil of this type is the ,chara1 which1 growing in masses together1 has sometimes been preserved in this way in large quantities1 indicating the existence of an ancient pond in the locality4 ,there is quite a variety of other types of preservation among fossil plants1 but they are of minor interest and importance1 and hardly justify detailed consideration4 ,one example that should be mentioned is ,amber4 ,this is the gum of old resinous trees1 and is a well-known substance which may rank as a 8fossil04 ,jet1 too1 is formed from plants1 while coal is so important that the whole of the next chapter will be devoted to its consideration4 ,even the black lead of pencils possibly represents plants that were once alive on this globe4 ,though such remains tell us of the existence of plants at the place they were found at a known period in the past1 yet they tell very little about the actual structure of the plants themselves1 and therefore very little that is of real use to the botanist4 ,fortunately1 however1 there are fossils which preserve every cell of the plant tissues1 each one perfect1 distended as in life1 and yet replaced by stone so as to be hard and to allow of the preparation of thin sections which can be studied with the microscope4 ,these are the vegetable fossils which are of prime importance to the botanist and the scientific enquirer into the evolution of plants4 ,such specimens are commonly known as ,petrifactions4 ,sometimes small isolated stumps of wood or branches have been completely permeated by silica1 which replaces the cell walls and completely preserves and hardens the tissues4 ,this silicified wood is found in a number of different beds of rock1 and may be seen washed out on the shore in ,yorkshire1 ,sutherland1 and other places where such rocks occur4 ,when such a block is cut and polished the annual rings and all the fine structure or 8grain0 of the wood become as apparent as in recent wood4 ,from these fossils1 too1 microscopic sections can be cut1 and then the individual wood cells can be studied almost as well as those of living trees4 ,a particularly notable example of fossil tree trunks is the ,tertiary forest of the ,yellowstone ,park4 ,here the petrified trunks are weathered out and stand together much as they must have stood when alive2 they are of course bereft of their foliage branches4 ,such specimens1 however1 are usually only isolated blocks of wood1 often fragments from large stumps which show nothing but the rings of late-formed wood4 ,it is impossible to connect them with the impressions of leaves or fruits in most cases1 so that of the plants they represent we know only the anatomical structure of the secondary wood and nothing of the foliage or general appearance of the plant as a whole4 ,hence these specimens also give a very partial representation of the plants to which they belonged4 ,fortunately1 however1 there is still another type of preservation of fossils1 a type more perfect than any of the others and sometimes combining the advantages of all of them4 ,this is the special type of petrifaction which includes1 not a single piece of wood1 but a whole mass of vegetation consisting of fragments of stems1 roots1 leaves1 and even seeds1 sometimes all together4 ,these petrifactions are those of masses of forest dbris which were lying as they dropped from the trees1 or had drifted together as such fragments do4 ,the plant tissues in such masses are preserved so that the most delicate soft tissue cells are perfect1 and in many cases the sections are so distinct that one might well be deluded into the belief that it is a living plant at which one looks4 ,very important and well-known specimens have been found in ,france and described by the ,french palobotanists4 ,as a rule these specimens are preserved in silica1 and are found now in irregular masses of the nature of chert4 ,of still greater importance1 however1 owing partly to their greater abundance and partly to the quantity of scientific work that has been done on them1 are the masses of stone found in the ,english coal seams and commonly called 8coal balls04 ,the 8coal balls0 are best known from ,lancashire and ,yorkshire1 where they are extremely common in some of the mines1 but they also occur in ,westphalia and other places on the ,continent4 ,illustration3 ,fig4 #aj4--,mass of ,coal with many 8coal balls0 embedded in it a a1 ,in surface view2 b b1 cut across4 ,all washed with acid to make the coal balls show up against the black coal4 7,photo by ,lomax47 ,in external appearance the 8coal balls0 are slightly irregular roundish masses1 most generally about the size of potatoes1 and black on the outside from films of adhering coal4 ,their size varies greatly1 and they have been found from that of peas up to masses with a diameter of a foot and a half4 ,they lie embedded in the coal and are not very easily recognizable in it at first1 because they are black also1 but when washed with acid they turn greyish-white and then can be recognized clearly4 ,fig4 #aj shows a block of coal with an exceptionally large number of the 8coal balls0 embedded in it4 ,this figure illustrates their slightly irregular rounded form in a typical manner4 ,by chemical analysis they are found to consist of a nearly pure mixture of the carbonates of lime and magnesia2 though in some specimens there is a considerable quantity of iron sulphide1 and in all there is at least #e per cent of various impurities and some quantity of carbon4 ,the important mineral compounds1 ,ca,c,o#c and ,mg,c,o#c1 are mixed in very different quantities1 and even in coal balls lying quite close to each other there is often much dissimilarity in this respect4 ,in whatever proportion these minerals are combined1 it seems to make but little difference to their preservative power1 and in good 8coal balls0 they may completely replace and petrify each individual cell of the plants in them4 ,illustration3 ,fig4 #aa4--,photograph of ,section across ,stem of ,sphenophyllum from a ,lancashire 8coal ball01 showing perfect preservation of woody tissue ,w1 wood2 c1 cortex4 ,fig4 #aa shows a section across the wood of a stem preserved in a 8coal ball01 and illustrates a degree of perfection which is not uncommon4 ,in the course of the succeeding chapters constant reference will be made to tissues preserved in 8coal balls01 and it may be noticed that not only the relatively hard woody cells are preserved but the very softest and youngest tissues also appear equally unharmed by their long sojourn in the rocks4 ,illustration3 ,fig4 #ab4--,photograph of ,section through a ,bud of ,lepidodendron1 showing many small leaves tightly packed round the axis4 ,from a 8coal ball0 ,the particular value of the coal balls as records of past vegetation lies in the fact that they are petrifactions1 not of individual plants alone1 but of masses of plant dbris4 ,hence in one of these stony concretions may lie twigs with leaves attached1 bits of stems with their fruits1 and fine rootlets growing through the mass4 ,a careful study and comparison of these fragments has led to the connection1 piece by piece1 of the various parts of many plants4 ,such a specimen as that figured in fig4 #ab shows how the soft tissues of young leaves are preserved1 and how their relation to each other and to the axis is indicated4 ,hitherto the only concretions of the nature of 8coal balls0 containing well preserved plant dbris1 have been found in the coal or immediately above it1 and are of ,palozoic age 7see p4 #cd74 ,recent exploration1 however1 has resulted in the discovery of similar concretions of ,mesozoic age1 from which much may be hoped in the future4 ,still1 at present1 it is to the palozoic specimens we must turn for nearly all valuable knowledge about ancient plants1 and primarily to that form of preservation of the specimens known as structural petrifactions1 of which the 8coal balls0 are both the commonest and the most perfect examples4 ,,chapter ,,iii ,,coal1 ,,the ,,most ,,important ,,of ,,plant ,,remains ,some of the many forms which are taken by fossil plants were shortly described in the last chapter1 but the most important of all1 namely coal1 must now be considered4 ,of the fossils hitherto mentioned many are difficult to recognize without examining them very closely1 and one might say that all have but little influence on human life1 for they are of little practical or commercial use1 and their scientific value is not yet very widely known4 ,of all fossil plants1 the great exception is coal4 ,its commercial importance all over the world needs no illustration1 and its appearance needs no description for it is in use in nearly every household4 ,quite apart from its economic importance1 coal has a unique place among fossils in the eyes of the scientist1 and is of special interest to the palontologist4 ,in ,england nearly all the coal lies in rocks of a great age1 belonging to a period very remote in the world's history4 ,the rocks bearing the coal contain other fossils1 principally those of marine animals1 which are characteristic of them and of the period during which they were formed1 which is generally known as the 8,coal ,measure period04 ,there is geological proof that at one time the coal seams were much more widely spread over ,england than they are at present2 they have been broken up and destroyed in the course of ages1 by the natural movements among the rocks and by the many changes and processes of disintegration and decay which have gone on ever since they were deposited4 ,to-day there are but relatively small coal-bearing areas1 which have been preserved in the hollows of the synclines4#b ,the seams of coal are extremely numerous1 and even the same seam may vary greatly in thickness4 ,from a quarter of an inch to five or six feet is the commonest thickness for coal in this country1 but there are many beds abroad of very much greater size4 ,thin seams often lie irregularly in coarse sandstone2 for example1 they may be commonly seen in the ,millstone ,grit2 but typical coal seams are found embedded between rocks of a more or less definite character known as the 8roof0 and 8floor04 ,illustration3 ,fig4 #ac4--;,diagram of a ,series of ,parallel ,coal ,seams with ,underclays and ,shale ,roofs of varying thicknesses ,basalts1 granites1 and such rocks do not contain coal2 the coal measures in which the seams of coal occur are1 generally speaking1 limestones1 fine sandstones1 and shales1 that is to say1 rocks which in their origin were deposited under water4 ,in detail almost every seam has some individual peculiarity1 but the following represents two types of typical seams4 ,in many cases1 below the coal1 the limestone or sandstone rocks give place to fine1 yellow-coloured layers of clay1 which varies from a few inches to many feet in thickness and is called the 8underclay04 ,this fine clay is generally free from pebbles and coarse dbris of all kinds1 and is often supposed to be the soil in which the plants forming the coal had been growing4 ,the line of demarcation between the coal and the clay is usually very sharp1 and the compact black layers of hard coal stop almost as abruptly on the upper side and give place to a shale or limestone 8roof02 see fig4 #ac1 layers #e1 #f1 and #g4 ,very frequently a number of small seams come together1 lying parallel1 and sometimes succeeding each other so rapidly that the 8roof0 is eliminated1 and a clay floor followed by a coal seam1 is succeeded immediately by another clay floor and another coal seam1 as in fig4 #ac1 layers #aj1 #aa1 and #ab4 ,the relative thickness of these beds also varies very greatly1 and over an underclay of seven or eight feet the coal seam may only reach a couple of inches1 while a thick seam may have a floor of very slight dimensions4 ,these relations depend on such a variety of local circumstances from the day they were forming1 that it is only possible to unravel the causes when an individual case is closely studied4 ,the main sequence1 however1 is constant and is that illustrated in fig4 #ac4 ,the second type of seam is that in which the underclay floor is not present1 and is replaced either by shales or by a special very hard rock of a finely granular nature called 8gannister04 ,in the gannister floor it is usual to find traces of rootlets and basal stumps of plants1 which seem to indicate that the gannister was the ground in which the plants forming the coal were rooted4 ,the coal itself is generally very pure plant remains1 though between its layers are often found bands of shaly stone which are called 8dirt bands04 ,these are particularly noticeable in thick seams1 and they may be looked on as corresponding to the roof shales2 as though1 in fact1 the roof had started to form but had only reached a slight development when the coal formation began again4 ,illustration3 ,fig4 #ad4--;,diagram of ,coal ,seam with ,gannister ,floor1 in which are traces of rootlets r1 and of stumps of root-like organs s ,that the coal is strikingly different from the rocks in which it lies is very obvious1 but that alone is no indication of its origin4 ,it is now so universally known and accepted that coal is the remains of vegetables that no proofs are usually offered for the statement4 ,it is1 however1 of both interest and importance to marshal the evidence for this belief4 ,the grounds for recognizing coal as consisting of practically pure plant remains are many and various1 so that only the more important of them will be considered now4 ,the most direct suggestion lies in the impressions of leaves and stems which are found between its layers2 this1 however1 is confronted by the parallel case of plant impressions found in shales and limestones which are not of vegetable origin1 so that it might be argued that those plants in the coal drifted in as did those in the limestone4 ,but when we examine the black impressions on limestone or sandstone1 an item of value is noticeable2 it is often possible to peel off a film1 lying between the upper and lower impression1 of black coaly substance1 sometimes an eighth of an inch thick1 and hard and shining like coal4 ,this follows the outline of the plant form of the impression1 and it is certain that this minute 8coal seam0 was formed from the plant tissues4 ,it is1 in fact1 a coal seam bearing the clearest possible evidence of its plant nature4 ,we have only to imagine this multiplied by many plants lying tightly packed together1 with no mineral impurities between1 to see that it would yield a coal seam like those we find actually existing4 ,in some cases in the coal itself a certain amount of the structure of the plants which formed it remains1 though usually1 in the process of their decay the tissues have entirely decomposed1 and left only their carbonized elements4 ,chemical analysis reveals that1 beyond the percentage of mineral ash which is found in living plants1 there is little in a pure sample of coal that is not carbonaceous4 ,all the deposits of carbon found in any form in nature can be traced to some animal or vegetable remains1 so that it is logical to assume that coal also arose from either animal or plant dbris4 ,but were coal of an animal origin1 the amount of mineral matter in it would be much larger as well as being of a different nature2 for almost all animals have skeletons1 even the simplest single-celled protozoa often own calcareous shells1 sponges have siliceous spicules1 molluscs hard shells1 and the higher animals bones and teeth4 ,these things are of a very permanent nature1 and would certainly be found in quantities in the coal had animals formed it4 ,further1 the peat of to-day1 which collects in thick compact masses of vegetable1 shows how plants may form a material consisting of carbonized remains4 ,by certain experiments in which peat was subjected to pressure and heat1 practically normal coal was made from it4 ,illustration3 ,fig4 #ae4--,part of a ,coal ,ball1 showing the concentric bandings in it which are characteristic of concretions ,illustration3 ,fig4 #af4--,mass of ,coal with ,coal ,balls1 ,a and ,b both enclosing part of the same stem ,l ,still a further witness may be found in the structure of the 8coal balls0 described in the last chapter4 ,these stony masses1 lying in the pure coal1 might well be considered as apart from it and bearing no relation to its structure2 but recent work has shown that they were actually formed at the same time as the coal1 developing in its mass as mineral concretions round some of the plants in the soft1 saturated1 peaty mass which was to be hardened into coal later on4#c ,all 8coal balls0 do not show their concretionary structure so clearly1 but sometimes it can be seen that they are made with concentric bands or markings like those characteristic of ordinary mineral concretions 7see fig4 #ae74 ,concretions are formed by the crystallization of minerals round some centre1 and it must have happened that in the coal seams in which the coal-ball concretions are found that this process took place in the soft plant mass before it hardened4 ,recent research has found that there is good evidence that those seams#d resulted from the slow accumulation of plant dbris under the salt or brackish water in whose swamps the plants were growing1 and that as they were collecting the ground slowly sank till they were quite below the level of the sea and were covered by marine silt4 ,at the same time some of the minerals present in the sea water1 which must have saturated the mass1 crystallized partly and deposited themselves round centres in the plant tissues1 and by enclosing them and penetrating them preserved them from decay till the mineral structure entirely replaced the cells1 molecule by molecule4 ,evidence is not wanting that this process went on without disturbance1 for in fig4 #af is shown a mass of coal in which lie several coal balls1 two of which enclose parts of the same plant4 ,this means that round different centres in the same stem two of the concretions were forming and preserving the tissues2 the two stone masses1 however1 did not enlarge enough to unite1 but left a part of the tissue unmineralized1 which is now seen as a streak of coal4 ,we have here the most important proof that the coal balls are actually formed in the coal and of the plants making the coal1 for had those coal balls come in as pebbles1 or in any way from the outside into the coal1 they could not have remained in such a position as to lie side by side enclosing part of the same stem4 ,there are many other details which may be used in this proof1 but this one illustration serves to show the importance of coal balls when dealing with the theories of the origin of coal1 for they are perfectly preserved samples of what the whole coal mass was at one time4 ,there are but few seams1 however1 which contain coal balls1 and about those in which they do not occur our knowledge is very scanty4 ,it is often assumed that the plant impressions in the shales above the coal seams can be taken as fair samples of those which formed the coal itself2 but this has been recently shown to be a fallacious argument in some cases1 so that it is impossible to rely on it in general4 ,the truth is1 that though coal is one of the most studied of all the geological deposits1 we are still profoundly ignorant of the details of its formation except in a few cases4 ,the way in which coal seams were formed has been described often and variously1 and for many years there were heated discussions between the upholders of the different views as to the merits of their various theories4 ,it is now certain that there must have been at least four principal ways in which coal was formed1 and the different seams are illustrations of the products of different methods4 ,in all cases more or less water is required1 for coal is what is known as a sedimentary deposit1 that is1 one which collects under water1 like the fine mud and silt and dbris in a lake4 ,it will be understood1 however1 that if the plant remains were collecting at any spot1 and the water brought in sand and mud as well1 then the deposit could not have resulted in pure coal1 but would have been a sandy mixture with many plant remains1 and would have resulted in the formation of a rock1 such as parts of the millstone grit1 where there are many streaks of coal through the stone4 ,among various coal seams1 evidence for the following modes of coal formation can be found3-- 7a7 ,in fresh water4--,in still freshwater lakes or pools1 with overhanging plants growing on the banks1 twigs and leaves which fell or were blown into the water became waterlogged and sank to the bottom4 ,with a luxuriant growth of plants rapidly collecting under water1 and there preserved from contact with the air and its decaying influence1 enough plant remains would collect to form a seam4 ,after that some change in the local conditions took place1 and other deposits covered the plants and began the accumulations which finally pressed the vegetable mass into coal4 ,to freshwater lakes of large size plants might also have been brought by rivers and streams2 they would have become waterlogged in time1 after floating farther than the sand and stones with which they came1 and would thus settle and form a deposit practically free from anything but plant remains4 7b7 ,as peat4--,peat commonly forms on our heather moors and bogs to-day to a considerable thickness4 ,this also took place long ago in all probability1 and when the level of the land altered it would have been covered by other deposits1 pressed1 and finally changed into coal4 7c7 ,in salt or brackish water1 growing in situ4--,trees and undergrowth growing thickly together in a salt or brackish marsh supplied a large quantity of dbris which fell into the mud or water below them1 and were thus shut off from the air and partly preserved4 ,when conditions favoured the formation of a coal seam the land level was slowly sinking1 and so1 though the dbris collected in large quantities1 it was always kept just beneath the water level4 ,finally the land sank more rapidly1 till the vegetable mass was quite under sea water1 then mud was deposited over it1 and the materials which were afterwards hardened to form the roof rocks were deposited4 ,this was the case in those seams in which 8coal balls0 occur1 and the evidence of the sea water covering the coal soon after it was deposited lies in the numerous sea shells found in the roof immediately above it4 7d7 ,in salt water1 drifted material4--,tree trunks and large tangled masses of vegetation drifted out to sea by the rivers just as they do to-day4 ,these became waterlogged1 and finally sank some distance from the shore4 7,those sinking near the shore would not form pure coal1 for sand and mud would be mixed with them1 also brought down by rivers and stirred up from the bottom by waves47 ,the currents would bring numbers of such plants to the same area until a large mass was deposited on the sea floor4 ,finally the local conditions would have changed1 the currents then bringing mud or sand1 which covered the vegetable mass and formed the mineral roof of the resulting coal seam4 ,there is a variety of what might be called the 8drifted coals01 which appears to have been formed of nothing but the spores of plants of a resinous nature4 ,these structures must have been very light1 and possibly floated a long distance before sinking4 ,if we could but obtain enough evidence to understand each case fully we should probably find that every coal seam represents some slightly different mode of formation1 that in each case there was some local peculiarity in the plants themselves and the way they accumulated in coal-forming masses1 but the above four methods will be found to cover the principal ways in which coal has arisen4 ,coal1 as we now know it1 has a great variety of qualities4 ,the differences probably depend only to a small extent on the varieties among the plants forming it1 and are almost entirely due to the many later conditions which have affected the coal after its original formation4 ,some such conditions are the various upheavals and depressions to which the rocks containing the coal have been subjected1 the weight of the beds lying over the coal seams1 and the high temperatures to which they may have been subjected when lying under a considerable depth of later-deposited rocks4 ,the influence on the coal of these and many other physical factors has been enormous1 but they are purely cosmical and belong to the special realm of geological study1 and so cannot be considered in detail now4 ,to return to our special subject1 namely1 the plants themselves which are now preserved in the coal4 ,their nature and appearance1 their affinities and minute structure1 can only be ascertained by a detailed study1 to which the following chapters will be devoted1 though in their limited space but an outline sketch of the subject can be drawn4 ,it has been stated by some writers that in the ,coal ,measure period plants were more numerous and luxuriant than they ever were before or ever have been since4 ,this view could only have been brought forward by one who was considering the geology of ,england alone1 and in any case there appears to be very little real evidence for such a view4 ,certainly in ,europe a large proportion of the coal is of this age1 and to supply the enormous masses of vegetation it represents a great growth of plants must have existed4 ,but it is evident that just at the ,carboniferous period in what is now called ,europe the physical conditions of the land which roughly corresponded to the present ,continent were such as favoured the accumulation of plants1 and the gradual sinking of the land level also favoured their preservation under rapidly succeeding deposits4 ,of the countless plants growing in ,europe to-day very few stand any chance of being preserved as coal for the future2 so that1 unless the physical conditions were suitable1 plants might have been growing in great quantity at any given period without ever forming coal4 ,but now that the geology of the whole world is becoming better known1 it is found that coal is by no means specially confined to the ,coal ,measure age4 ,even in ,europe coals of a much later date are worked1 while abroad1 especially in ,asia and ,australia1 the later coals are very important4 ,for example1 in ,japan1 seams of coal #ad1 #bj1 and even more feet in thickness are worked which belong to the ,tertiary period 7see p4 #cd71 while in ,manchuria coal #ajj feet thick is reported of the same age4 ,when these facts are considered it is soon found that all the statements made about the unique vegetative luxuriance of the ,coal ,measure period are founded either on insufficient evidence or on no evidence at all4 ,the plants forming the later coals must have had in their own structure much that differed from those forming the old coals of ,britain1 and the gradual change in the character of the vegetation in the course of the succeeding ages is a point of first-rate importance and interest which will be considered shortly in the next chapter4 ,,chapter ,,iv ,,the ,,seven ,,ages ,,of ,,plant ,,life ,life has played its important part on the earth for countless series of years1 of the length of whose periods no one has any exact knowledge4 ,many guesses have been made1 and many scientific theories have been used to estimate their duration1 but they remain inscrutable4 ,when numbers are immense they cease to hold any meaning for us1 for the human mind cannot comprehend the significance of vast numbers1 of immense space1 or of ons of time4 ,hence when we look back on the history of the world we cannot attempt to give even approximate dates for its events1 and the best we can do is to speak only of great periods as units whose relative position and whose relative duration we can estimate to some extent4 ,those who have studied geology1 which is the science of the world's history since its beginning1 have given names to the great epochs and to their chief subdivisions4 ,with the smaller periods and the subdivisions of the greater ones we will not concern ourselves1 for our study of the plants it will suffice if we recognize the main sequence of past time4 ,the main divisions are practically universal1 and evidence of their existence and of the character of the creatures living in them can be found all over the world2 the smaller divisions1 however1 may often be local1 or only of value in one continent4 ,to the specialist even the smallest of them is of importance1 and is a link in the chain of evidence with which he cannot dispense2 but we are at present concerned only with the broad outlines of the history of the plants of these periods1 so will not trouble ourselves with unnecessary details4#e ,corresponding to certain marked changes in the character of the vegetation1 we find seven important divisions of geological time which we will take as our unit periods1 and which are tabulated as follows3-- ,cainozoic ,i4 ,present ,day4 ,,ii4 ,tertiary4 ,mesozoic ,,iii4 ,upper ,cretaceous 7or ,chalk74 ,,iv4 ,the rest of the ,mesozoic4 ,v4 ,newer ,palozoic1 including ,permian4 ,carboniferous4 ,devonian4 ,palozoic ,,vi4 ,older ,palozoic4 ,eozoic ,,vii4 ,archan4 ,now the actual length of these various periods was very different4 ,the epoch of the ,present ,day is only in its commencement1 and is like a thin line if compared with the broad bands of the past epochs4 ,by far the greatest of the periods is the ,archan1 and even the ,older ,palozoic is probably longer than all the others taken together4 ,it is1 however1 so remote1 and the rocks which were formed in it retain so little plant structure that is decipherable1 so few specimens which are more than mere fragments1 that we know very little about it from the point of view of the plant life of the time4 ,it includes the immense indefinite epochs when plants began to evolve1 and the later ones when animals of many kinds flourished1 and when plants1 too1 were of great size and importance1 though we are ignorant of their structure4 ,of all the seven divisions of time1 we can say least about the two earliest1 simply for want of anything to say which is founded on fact rather than on theoretical conclusions4 ,although these periods seem clearly marked off from one another when looked at from a great distance1 they are1 of course1 but arbitrary divisions of one long1 continuous series of slow changes4 ,it is not in the way of nature to make an abrupt change and suddenly shut off one period--be it a day or an on--from another1 and just as the seasons glide almost imperceptibly into one another1 so did the great periods of the past4 ,thus1 though there is a strong and very evident contrast between the plants typical of the ,carboniferous period and of the ,mesozoic1 those of the ,permian are to some extent intermediate1 and between the beginning of the ,permian and the end of the ,carboniferous--if judged by the flora--it is often hard to decide4 ,it must be realized that almost any given spot of land--the north of ,england1 for example--has been beneath the sea1 and again elevated into the air1 at least more than once4 ,that the hard rocks which make its present-day hills have been built up from the silt and dbris under an ocean1 and after being formed have seen daylight on a land surface long ago1 and sunk again to be covered by newer deposits1 perhaps even a second or a third time1 before they rose for the time that is the present4 ,yet all these profound changes took place so slowly that had we been living then we could have felt no motion1 just as we feel no motion to-day1 though the land is continuing to change all around us4 ,the great alternations between land and water over large areas mark out to some extent the main periods tabulated on p4 #cd1 for after each great submersion the rising land seems to have harboured plants and animals with somewhat different characters from those which inhabited it before4 ,similarly1 when the next submersion laid down more rocks of limestone and sandstone1 they enclosed the shells of some creatures different from those which had inhabited the seas of the region previously4 ,through all the periods the actual rocks formed are very similar--shales1 limestones1 sandstones1 clays4 ,when any rocks happen to have preserved neither plant nor animal remains it is almost impossible to tell to which epoch they belong1 except from a comparative study of their position as regards other rocks which do retain fossils4 ,this depends on the fact that the physical processes of rock building have gone on throughout the history of the globe on very much the same lines as they are following at present4 ,by the sifting power of water1 fine mud1 sand1 pebbles1 and other dbris are separated from each other and collected in masses like to like4 ,the fine mud will harden into shales1 sandgrains massed together harden into sandstones1 and so on1 and when1 after being raised once more to form dry land1 they are broken up by wind and rain and brought down again to the sea1 they settle out once again in a similar way and form new shales and sandstones2 and so on indefinitely4 ,but meantime the living things1 both plant and animal1 have been changing1 growing1 evolving1 and the leafy twig brought down with the sandgrains in the flooded river of one epoch differs from that brought down by the river of a succeeding epoch--though it might chance that the sandgrains were the same identical ones4 ,and hence it is by the remains of the plants and animals in a rock that we can tell to which epoch it belonged4 ,unless1 of course1 ready-formed fossils from an earlier epoch get mixed with it1 coming as pebbles in the river in flood--but that is a subtle point of geological importance which we cannot consider here4 ,such cases are almost always recognizable1 and do not affect the main proposition4 ,from the various epochs1 the plants which have been preserved as fossils are in nearly all cases those which had lived on the land1 or at least on swamps and marshes by the land4 ,of water plants in the wide sense1 including both those growing in fresh water and those in the sea1 we have comparatively few4 ,this lack is particularly remarkable in the case of the seaweeds1 because they were actually growing in the very medium in which the bulk of the rocks were formed1 and which we know from recent experiments acts as a preservative for the tissues of land plants submerged in it4 ,it must be remembered1 however1 that almost all the plants growing in water have very soft tissues1 and are usually of small size and delicate structure as compared with land plants1 and thus would stand less chance of being preserved1 and would also stand less chance of being recognized to-day were they preserved4 ,the mark on a stone of the impression of a soft film of a waterweed would be very slight as compared with that left by a leathery leaf or the woody twig of a land plant4 ,there are1 of course1 exceptions1 and1 as will be noted later on 7see ,chapter ,,xvii71 there are fossil seaweeds and fossil freshwater plants1 but we may take it on the whole that the fossils we shall have to deal with and that give important evidence1 are those of the land which had drifted out to sea1 in the many cases when they are found in rocks together with sea shells4 ,let us now consider very shortly the salient features of the seven epochs we have named as the chief divisions of time4 ,the vegetation of the ,carboniferous ,period is better known to us than that of any other period except that of the present day1 so that it will form the best starting-point for our consideration4 ,at this period there were1 as there are to-day1 oceans and continents1 high lands1 low lands1 rivers and lakes1 in fact1 all the physical features of the present-day world1 but they were all in different places from those of to-day4 ,if we confine our attention to ,britain1 we find that at that period the far north1 ,scotland1 ,wales1 and ,charnwood were higher land1 but the bulk of the southern area was covered by flat swamps or shallow inlets1 where the land level gradually changed1 slowly sinking in one place and slowly rising in others1 which later began also to sink4 ,growing on this area wherever they could get a foothold were many plants1 all different from any now living4 ,among them none bore flowers4 ,a few families bore seeds in a peculiar way1 differing widely from most seed-bearing plants of to-day4 ,the most prevalent type of tree was that of which a stump is represented in the frontispiece1 and of which there were many different species4 ,these plants1 though in size and some other ways similar to the great trees of to-day1 were fundamentally different from them1 and belonged to a very primitive family1 of which but few and small representatives now exist1 namely the ,lycopods4 ,many other great trees were like hugely magnified 8horsetails0 or ,equisetums2 and there were also seed-bearing ,gymnosperms of a type now extinct4 ,there were ferns of many kinds1 of which the principal ones belong to quite extinct families1 as well as several other plants which have no parallel among living ones4 ,hence one may judge that the vegetation was rich and various1 and that1 as there were tall trees with seeds1 the plants were already very highly evolved4 ,indeed1 except for the highest group of all1 the flowering plants1 practically all the main groups now known were represented4 ,the flora of the ,devonian was very similar in essentials4 ,if that be so1 it may seem unsatisfactory to place all the preceding ons under one heading1 the ,older ,palozoic4 ,and1 indeed1 it is very unsatisfactory to be forced to do so4 ,we know from the study of animal fossils that this time was vast1 and that there were several well-defined periods in it during which many groups of animals evolved1 and became extinct after reaching their highest development2 but of the plants we know so little that we cannot make any divisions of time which would be of real value in helping us to understand them4 ,fossil plants from the ,early ,palozoic there are1 but extremely few as compared with the succeeding period1 and those few but little illuminative4 ,in the later divisions of the ,pre-,carboniferous some of the plants seem to belong to the same genera as those of the ,carboniferous period4 ,there is a fern which is characteristic of one of the earlier divisions1 and there are several rather indefinite impressions which may be considered as seaweeds4 ,there is evidence also that even one of the higher groups bearing seeds 7the ,cordaite7 was in full swing long before the ,carboniferous period began4 ,hence1 though of ,older ,palozoic plants we know little of actual fact1 we can surmise the salient truths2 viz41 that in that period those plants must have been evolving which were important in the ,devonian and ,carboniferous periods2 that in the earlier part of that period they did not exist1 and the simpler types only clothed the earth2 and that further back still1 even the simpler types had not yet evolved4 ,names have been given to many fragmentary bits of fossils1 but for practical purposes we might as well be without them4 ,for the present the actual plants of the ,older ,palozoic must remain in a misty obscurity1 their forms we can imagine1 but not know4 ,on the other hand1 of the more recent periods1 those succeeding the ,carboniferous1 we have a little more knowledge4 ,yet for all these periods1 even the ,tertiary immediately preceding the present day1 our knowledge is far less exact and far less detailed than it is for that unique period1 the ,carboniferous itself4 ,the characteristic plants of the ,carboniferous period are all very different from those of the present1 and every plant of that date is now extinct4 ,in the succeeding periods the main types of vegetation changed1 and with each succeeding change advanced a step towards the stage now reached4 ,the ,permian1 geologically speaking1 was a period of transition4 ,toward the close of the ,carboniferous there were many important earth movements which raised the level of the land and tended to enclose the area of water in what is now ,eastern ,europe1 and to make a continental area with inland seas4 ,many of the ,carboniferous genera are found to extend through the ,permian and then die out1 while at the same time others became quite extinct as the physical conditions changed4 ,the seed-bearing plants became relatively more important1 and though the genus ,cordaites died out at the end of the period it was succeeded by an increasing number of others of more advanced type4 ,when we come to the older ,mesozoic rocks1 we have in ,england at any rate an area which was slowly submerging again4 ,the more important of the plants which are preserved1 and they are unfortunately all too few1 are of a type which has not yet appeared in the earlier rocks1 and are in some ways like the living ,cycas1 though they have many characters fundamentally different from any living type4 ,in the vegetation of this time1 plants of ,cycad-like appearance seem to have largely predominated1 and may certainly be taken as the characteristic feature of the period4 ,the great ,lycopod and ,equisetum-like trees of the ,carboniferous are represented now only by smaller individuals of the same groups1 and practically all the genera which were flourishing in the ,carboniferous times have become extinct4 ,the ,cycad-like plants1 however1 were far more numerous and varied in character and widely spread than they ever were in any succeeding time4 ,still1 no flowers 7as we understand the word to-day7 had appeared1 or at least we have no indication in any fossil hitherto discovered1 that true flowers were evolved until towards the end of the period 7see1 however1 ,chapter ,x74 ,the newer ,mesozoic or ,upper ,cretaceous period represents a relatively deep sea area over ,england1 and the rocks then formed are now known as the chalk1 which was all deposited under an ocean of some size whose water must have been clear1 and on the whole free from ordinary dbris1 for the chalk is a remarkably homogeneous deposit4 ,from the point of view of plant history1 the ,upper ,mesozoic is notable1 because in it the flowering plants take a suddenly important position4 ,beds of this age 7though of very different physical nature7 are known all over the world1 and in them impressions of leaves and fruits1 or their casts1 are well represented4 ,the leaves are those of both ,monocotyledons and ,dicotyledons1 and the genera are usually directly comparable with those now living1 and sometimes so similar that they appear to belong to the same genus4 ,the cone-bearing groups of the ,gymnosperms are still present and are represented by a number of forms1 but they are far fewer in varieties than are the groups of flowering plants--while the ,cycad-like plants1 so important in the ,lower ,mesozoic1 have relatively few representatives4 ,there is1 it almost seems1 a sudden jump from the flowerless type of vegetation of the ,lower ,mesozoic1 to a flora in the ,upper ,mesozoic which is strikingly like that of the present day4 ,the ,tertiary period is a short one 7geologically speaking1 and compared with those going before it71 and during it the land level rose again gradually1 suffering many great series of earth movements which built most of the mountain chains in ,europe which are standing to the present day4 ,in the many plant-containing deposits of this age1 we find specimens indicating that the flora was very similar to the plants now living1 and that flowering plants held the dominant position in the forests1 as they do to-day4 ,in fact1 from the point of view of plant evolution1 it is almost an arbitrary and unnecessary distinction to separate the ,tertiary epoch from the present1 because the main features of the vegetation are so similar4 ,there are1 however1 such important differences in the distribution of the plants of the ,tertiary and those of the present times1 that the distinction is advisable2 but it must always be remembered that it is not comparable with the wide differences between the other epochs4 ,among the plants now living we find representatives of most1 though not of all1 of the great groups of plants which have flourished in the past1 though in the course of time all the species have altered and those of the earliest earth periods have become extinct4 ,the relative importance of the different groups changes greatly in the various periods1 and as we proceed through the ages of time we see the dominant place in the plant world held successively by increasingly advanced types1 while the plants which dominated earlier epochs dwindle and take a subordinate position4 ,for example1 the great trees of the ,carboniferous period belonged to the ,lycopod family1 which to-day are represented by small herbs creeping along the ground4 ,the ,cycad-like plants of the ,mesozoic1 which grew in such luxuriance and in such variety1 are now restricted to a small number of types scattered over the world in isolated localities4 ,during all the periods of which we have any knowledge there existed a rich and luxuriant vegetation composed of trees1 large ferns1 and small herbs of various kinds1 but the members of this vegetation have changed fundamentally with the changing earth1 and unlike the earth in her rock-forming they have never repeated themselves4 ,,chapter ,v ,,stages ,,in ,,plant ,,evolution ,to attempt any discussion of the causes of evolution is far beyond the scope of the present work4 ,at present we must accept life as we find it1 endowed with an endless capacity for change and a continuous impulse to advance4 ,we can but study in some degree the course taken by its changes4 ,from the most primitive beginnings of the earliest periods1 enormous advance had been made before we have any detailed records of the forms4 ,yet there remain in the world of to-day numerous places where the types with the simplest structure can still flourish1 and successfully compete with higher forms4 ,many places which1 from the point of view of the higher plants1 are undesirable1 are well suited to the lower4 ,such places1 for example1 as the sea1 and on land the small nooks and crannies where water drops collect1 which are useless for the higher plants1 suffice for the minute forms4 ,in some cases the lower plants may grow in such masses together as to capture a district and keep the higher plants from it4 ,equisetum 7the horsetail7 does this by means of an extensive system of underground rhizomes which give the plant a very strong hold on a piece of land which favours it1 so that the flowering plants may be quite kept from growing there4 ,in such places1 by a variety of means1 plants are now flourishing on the earth which represent practically all the main stages of development of plant life as a whole4 ,it is to the study of the simpler of the living forms that we owe most of our conceptions of the course taken by evolution4 ,had we to depend on fossil evidence alone1 we should be in almost complete ignorance of the earliest types of vegetation and all the simpler cohorts of plants1 because their minute size and very delicate structure have always rendered them unsuitable for preservation in stone4 ,at the same time1 had we none of the knowledge of the numerous fossil forms which we now possess1 there would be great gaps in the series which no study of living forms could supply4 ,it is only by a study and comparison of both living and fossil plants of all kinds and from beds of all ages that we can get any true conception of the whole scheme of plant life4 ,grouping together all the main families of plants at present known to us to exist or to have existed1 we get the following series3-- ,group4 ,common examples of typical families in the group4 ,thallophyta ,alg ,seaweeds4 ,fungi ,moulds and toadstools4 ,bryophyta ,hepatic ,liverworts4 ,musci ,mosses4 ,pteridophyta ,equisetales ,horsetails4 ,sphenophyllales99 fossil only1 ,sphenophyllum4 ,lycopodales ,club-moss4 ,filicales ,bracken fern4 ,pteridosperm ,lyginodendr99 fossil only1 ,sphenopteris4 ,gymnosperms ,cycadales ,cycads4 ,bennettitales99 fossil only1 ,bennettites4 ,ginkgoales ,maidenhair ,tree4 ,cordaitales99 fossil only1 ,cordaites4 ,coniferales ,pine1 ,yew4 ,gnetales ,welwitschia4 ,angiosperms ,monocotyledons ,lily1 ,palm1 ,grass4 ,dicotyledons ,rose1 ,oak1 ,daisy4 ,in this table the different groups have not a strictly equivalent scientific value1 but each of those in the second column represents a large and well-defined series of primary importance1 whose members could not possibly be included along with any of the other groups4 ,those marked with an asterisk are known only as fossils1 and it will be seen that of the seventeen groups1 so many as four are known only in the fossil state4 ,this indicates1 however1 but a part of their importance1 for in nearly every other group are many families or genera which are only known as fossils1 though there are living representatives of the group as a whole4 ,in this table the individual families are not mentioned1 because for the present we need only the main outline of classification to illustrate the principal facts about the course of evolution4 ,as the table is given1 the simplest families come first1 the succeeding ones gradually increasing in complexity till the last group represents the most advanced type with which we are acquainted1 and the one which is the dominant group of the present day4 ,this must not be taken as a suggestion that the members of this series have evolved directly one from the other in the order in which they stand in the table4 ,that is indeed far from the case1 and the relations between the groups are highly complex4 ,it must be remarked here that it is often difficult1 even impossible1 to decide which are the most highly evolved members of any group of plants4 ,each individual of the higher families is a very complicated organism consisting of many parts1 each of which has evolved more or less independently of the others in response to some special quality of the surroundings4 ,for instance1 one plant may require1 and therefore evolve1 a very complex and well-developed water-carriage system while retaining a simple type of flower2 another may grow where the water problem does not trouble it1 but where it needs to develop special methods for getting its ovules pollinated2 and so on1 in infinite variety4 ,as a result of this1 in almost all plants we have some organs highly evolved and specialized1 and others still in a primitive or relatively primitive condition4 ,it is only possible to determine the relative positions of plants on the scale of development by making an average conclusion from the study of the details of all their parts4 ,this1 however1 is beset with difficulties1 and in most cases the scientist1 weighed by personal inclinations1 arbitrarily decides on one or other character to which he pays much attention as a criterion1 while another scientist tends to lay stress on different characters which may point in another direction4 ,in no group is this better illustrated than among the ,conifer1 where the relative arrangement of the different families included in it is still very uncertain1 and where the observations of different workers1 each dealing mainly with different characters in the plants1 tend to contradict each other4 ,this1 however1 as a byword4 ,notwithstanding these difficulties1 which it would be unfair to ignore1 the main scheme of evolution stands out clearly before the scientist of to-day1 and his views are largely supported by many important facts from both fossil and living plants4 ,very strong evidence points to the conclusion that the most primitive plants of early time were1 like the simplest plants of to-day1 water dwellers4 ,whether in fresh water or the sea is an undecided point1 though opinion seems to incline in general to the view that the sea was the first home of plant life4 ,it can1 however1 be equally well1 and perhaps even more successfully argued1 that the freshwater lakes and streams were the homes of the first families from which the higher plants have gradually been evolved4 ,for this there is no direct evidence in the rocks1 for the minute forms of the single soft cells assumed by the most primitive types were just such as one could not expect to be successfully fossilized4 ,hence the earliest stages must be deduced from a comparative study of the simplest plants now living4 ,fortunately there is much material for this in the numerous waters of the earth1 where swarms of minute types in many stages of complexity are to be found4 ,the simplest type of plants now living1 which appears to be capable of evolution on lines which might have led to the higher plants1 is that found in various members of the group of the ,protococcoide among the ,alg4 ,the claim of bacteria and other primitive organisms of various kinds to the absolute priority of existence is one which is entirely beyond the scope of a book dealing with fossil plants4 ,the early evolution of the simple types of the ,protococcoide is also somewhat beyond its scope1 but as they appear to lie on the most direct 8line of descent0 of the majority of the higher plants it cannot be entirely ignored4 ,from the simpler groups of the green ,alg other types have specialized and advanced along various directions1 but among them there seems an inherent limitation1 and none but the protococcoid forms seem to indicate the possibility of really high development4 ,illustration3 ,fig4 #ag4--;,a ,protococcoid ,plant consisting of one cell p1 ,protoplasm2 n1 nucleus2 g1 colouring body or chloroplast2 w1 cell wall4 ,in a few words1 a typical example of one of the simple ,protococcoide may be described as consisting of a mass of protoplasm in which lie a recognizable nucleus and a green colouring body or chloroplast1 with a cell wall or skin surrounding these vital structures1 a cell wall that may at times be dispensed with or unusually thickened according as the need arises4 ,this plant is represented in fig4 #ag in a somewhat diagrammatic form4 ,in such a case the whole plant consists of one single cell1 living surrounded by the water1 which supplies it with the necessary food materials1 and also protects it from drying up and from immediate contact with any hard or injurious object4 ,when these plants propagate they divide into four parts1 each one similar to the original cell1 which all remain together within the main cell wall for a short time before they separate4 ,if now we imagine that the four cells do not separate1 but remain together permanently1 we can see the possibility of a beginning of specialization in the different parts of the cell4 ,the single living cell is equally acted on from all sides1 and in itself it must perform all the life functions2 but where four lie together1 each of the four cells is no longer equally acted on from all sides4 ,this shows clearly in the diagram of a divided cell given in fig4 #ah4 ,here it is obvious that one side of each of the four cells1 viz4 that named a in the diagram1 is on the outside and in direct contact with the water and external things2 but walls b and c touch only the corresponding walls of the neighbouring cells4 ,through walls b and c no food and water can enter directly1 but at the same time they are protected from injury and external stimulus4 ,hence1 in this group of four cells there is a slight differentiation of the sides of the cells4 ,if now we imagine that each of the four cells1 still remaining in contact1 divides once more into four members1 each of which reaches mature size while all remain together1 then we have a group of sixteen cells1 some of which will be entirely inside1 and some of which will have walls exposed to the environment4 ,illustration3 ,fig4 #ah4--;,diagram of ,protococcoid ,cell divided into four daughter cells4 ,walls a are external1 and walls b and c in contact with each other4 ,if the cells of the group all divide again1 in the manner shown the mass will become more than one cell thick1 and the inner cells will be more completely differentiated1 for they will be entirely cut off from the outside and all direct contact with water and food materials1 and will depend on what the outer cells transmit to them4 ,the outer cells will become specialized for protection and also for the absorption of the water and salts and air for the whole mass4 ,from such a plastic group of green cells it is probable that the higher and increasingly complex forms of plants have evolved4 ,there are still living plants which correspond with the groups of four1 sixteen1 c41 cells just now theoretically stipulated4 ,illustration3 ,fig4 #ai4--;,a1 ,details of ,part of the ,tissues in a ,stem of a ,flowering ,plant4 ,b1 ,diagram of the ,whole ,arrangement of ,cross ,section of a ,stem3 e1 ,outer protecting skin2 g1 green cells2 s1 thick-walled strengthening cells2 p1 general ground tissue cells4 ,v1 ,groups of special conducting tissues3 x1 vessels for water carriage2 px1 first formed of the water vessels2 c1 growing cells to add to the tissues2 b1 food-conducting cells2 ss1 strengthening cells4 ,the higher plants of to-day all consist of very large numbers of cells forming tissues of different kinds1 each of which is specialized more or less1 some very elaborately1 for the performance of certain functions of importance for the plant body as a whole4 ,with the increase in the number of cells forming the solid plant body1 the number of those living wholly cut off from the outside becomes increasingly great in comparison with those forming the external layer4 ,some idea of the complexity and differentiation of this cell mass is given in fig4 #ai1 ,a1 which shows the relative sizes and shapes of the cells composing a small part of the stem of a common flowering plant4 ,the complete section would be circular and the groups ,v would be repeated round it symmetrically1 and the whole would be enclosed by an unbroken layer of the cells marked e1 as in the diagram ,b4 ,illustration3 ,fig4 #bj4--;,conducting ,cells and ,surrounding ,tissue seen in fig4 #ai1 ,a1 cut lengthways4 px1 ,first formed vessels for water conduction2 x1 larger vessel2 b1 food-conducting cells2 ss1 strengthening cells2 p1 general ground tissue4 ,in the tissues of the higher plants the most important feature is the complex system of conducting tissues1 shown in the young condition in ,v in fig4 #ai1 ,a4 ,in them the food and water conducting elements are very much elongated and highly specialized cells1 which run between the others much like a system of pipes in the brickwork of a house4 ,these cells are shown cut longitudinally in fig4 #bj1 where they are lettered to correspond with the cells in fig4 #ai1 ,a1 with which they should be compared4 ,in such a view the great difference between the highly specialized cells x1 px1 b1 c41 and those of the main mass of ground tissue p becomes apparent4 ,even in the comparatively simply organized groups of the ,equisetales and ,lycopodiales the differentiation of tissues is complete4 ,in the mosses1 and still more in the liverworts1 it is rudimentary2 but they grow in very damp situations1 where the conduction of water and the protection from too much drying is not a difficult problem for them4 ,as plants grow higher into the air1 or inhabit drier situations1 the need of specialization of tissues becomes increasingly great1 for they are increasingly liable to be dried1 and therefore need a better flow of water and a more perfect protective coat4 ,it is needless to point out how the individual cells of a plant1 such as that figured in figs4 #ai and #bj1 have specialized away from the simple type of the protococcoid cell in their mature form4 ,in the young growing parts of a plant1 however1 they are essentially like protococcoid cells of squarish outline1 fitting closely to each other to make a solid mass1 from which the individual types will differentiate later and take on the form suitable for the special part they have to play in the economy of the whole plant4 ,to trace the specialization not only of the tissues but of the various parts of the whole plant which have become elaborate organs1 such as leaves1 stems1 and flowers1 is a task quite beyond the present work to attempt4 ,from the illustrations given of tissue structure from plants at the two ends of the series much can be imagined of the inevitable intermediate stages in tissue evolution4 ,as regards the elaboration of organs1 and particularly of the reproductive organs1 details will be found throughout the book4 ,in judging of the place of any plant in the scale of evolution it is to the reproductive organs that we look for the principal criteria1 for the reproductive organs tend to be influenced less by their physical surroundings than the vegetative organs1 and are therefore truer guides to natural relationships4 ,in the essential cells of the reproductive organs1 viz4 the egg cell and the male cell1 we get the most primitively organized cells in the plant body4 ,in the simpler families both male and female cells return to the condition of a free-swimming protococcoid cell1 and in all but the highest families the male cell requires a liquid environment1 in which it swims to the egg cell4 ,in the higher families the necessary water is provided within the structure of the seed1 and the male cell does not swim1 a naked1 solitary cell1 out into the wide world1 as it does in all the families up to and including the ,filicales4 ,in the ,conifer and ,angiosperms the male cell does not swim1 but is passive 7or largely so71 and is brought to the egg cell4 ,one might almost say that the whole evolution of the complex structures found in fruiting cones and flowers is a result of the need of protection of the delicate1 simple reproductive cells and the embryonic tissues resulting from their fusion4 ,the lower plants scatter these delicate cells broadcast in enormous numbers1 the higher plants protect each single egg cell by an elaborate series of tissues1 and actually bring the male cell to it without ever allowing either of them to be exposed4 ,it must be assumed that the reader possesses a general acquaintance with the living families tabulated on p4 #dd2 those of the fossil groups will be given in some detail in succeeding chapters which deal with the histories of the various families4 ,it is premature to attempt any general discussion of the evolution of the various groups till all have been studied1 so that this will be reserved for the concluding chapters4 ,,chapter ,,vi ,,minute ,,structure ,,of ,,fossil ,,plants--,,likenesses ,,to ,,living ,,ones ,the individual plants of the ,coal ,measure period differed entirely from those now living2 they were more than merely distinct species1 for in the main even the families were largely different from the present ones4 ,nevertheless1 when we come to examine the minute anatomy of the fossils1 and the cells of which they are composed1 we find that between the living and the fossil cell types the closest similarity exists4 ,from the earliest times of which we have any knowledge the elements of the plant body have been the same1 though the types of structures which they built have varied in plan4 ,individual cells of nearly every type from the ,coal ,measure period can be identically matched with those of to-day4 ,in the way the walls thickened1 in the shapes of the wood1 strengthening or epidermal cells1 in the form of the various tissues adapted to specific purposes1 there is a unity of organization which it is reasonable to suppose depends on the fundamental qualities inherent in plant life4 ,this will be illustrated best1 perhaps1 by tabulating the chief modifications of cells which are found in plant tissues4 ,the illustrations of these types in the following table are taken from living plants1 because from them figures of more diagrammatic clearness can be made1 and the salient characters of the cells more easily recognized4 ,comparison of these typical cells with those illustrated from the fossil plants reveals their identity in essential structure1 and most of them will be found in the photos of fossils in these pages1 though they are better recognized in the actual fossils themselves4 ,principal ,types of ,plant ,cells ,epidermal4 ,illustration3 ,fig4 #ba ,epidermis4--,protecting layer or skin4 ,cells with outer wall thickened in many cases 7fig4 #ba1 a and b74 ,compare fossil epidermis in fig4 #cd1 e4 ,illustration3 ,fig4 #bb ,hairs4--,extensions of epidermis cells4 ,single cells1 or complex1 as fig4 #bb1 h1 where e is epidermis and p parenchyma4 ,compare fossil hairs in figs4 #gi and #abj4 ,illustration3 ,fig4 #bc ,stomates4--,breathing pores in the epidermis4 ,seen in surface view as two-lipped structures 7fig4 #bc74 s1 ,stomates2 e1 epidermis cells4 ,compare fossil stomates in fig4 #h4 ,ground ,tissue ,illustration3 ,fig4 #bd ,parenchyma4--,simple soft cells1 either closely packed1 as in fig4 #bd1 or with air spaces between them4 ,compare #gh1 ,b1 for fossil4 ,illustration3 ,fig4 #be ,palisade4--,elongated1 closely packed cells1 p1 chiefly in leaves1 lying below the epidermis1 e1 fig4 #be4 ,compare fig4 #cd1 p1 for fossil palisade4 ,illustration3 ,fig4 #bf ,endodermis4--,cells with specially thickened walls1 en1 lying as sheath between the parenchyma1 c1 of ground tissue1 and the vascular tissue1 s1 fig4 #bf4 ,compare fig4 #ajh for fossil endodermis4 ,illustration3 ,fig4 #bg ,latex cells4--,large1 often much elongated cells1 m1 lying in the parenchyma1 p1 fig4 #bg1 which are packed with contents4 ,compare fig4 #ajg1 s4 ,illustration3 ,fig4 #bh ,sclerenchyma4--,thick-walled cells among parenchyma for strengthening1 fig4 #bh4 ,compare fig4 #cd1 s4 ,illustration3 ,fig4 #bi ,cork4--,layers of cells replacing the epidermis in old stems4 ,outer cells1 o1 crushed2 k1 closely packed cork cells2 stone cells1 s1 fig4 #bi4 ,compare fig4 #ie1 k4 ,cork cambium4--,narrow1 actively dividing cells1 c in fig4 #bi1 giving rise to new cork cells in consecutive rows4 ,illustration3 ,fig4 #cj ,tracheides4--,specially thickened cells in the parenchyma1 usually for water storage1 t1 fig4 #cj4 ,compare fig4 #ie1 t4 ,vascular ,tissue ,illustration3 ,fig4 #ca ,wood4--,protoxylem1 tracheids and vessels1 long1 narrow elements1 with spiral or ring-like thickenings1 s#a and s#b1 fig4 #ca4 ,compare fig4 #ha1 ,a1 px1 for fossil4 ,metaxylem1 long elements1 tracheids and vessels4 ,some with narrow pits1 as t in fig4 #ca2 others with various kinds of pits4 ,in transverse section seen in fig4 #cc1 w1 fossil in fig4 #aad1 w4 ,wood parenchyma4--,soft cells associated with the wood1 p in fig4 #ca4 ,fossil in fig4 #ha1 ,b1 p4 ,wood sclerenchyma4--,hard thickened cells in the wood4 ,illustration3 ,fig4 #cb ,bast4--,sieve tubes1 long cells which carry foodstuffs1 cross walls pitted like sieves1 s1 fig4 #cb4 ,in transverse section in fig4 #cc4 ,companion cells1 narrow cells with rich proteid contents1 c1 fig4 #cb4 ,in transverse section at c1 fig4 #cc4 ,bast parenchyma4--,soft unspecialized cells mixed with the sieve tubes1 p1 fig4 #cb4 ,bast fibres4--,thick-walled sclerenchymatous cells mixed with1 or outside1 the soft bast4 ,illustration3 ,fig4 #cc ,cambium4--,narrow cells1 like those of the cork cambium1 which lie between the wood and bast1 and give rise to new tissues of each kind1 cb1 fig4 #cc4 ,compare fig4 #aad1 fossil4 ,there are1 of course1 many minor varieties of cells1 but these illustrate all the main types4 ,among the early fossils1 however1 one type of wood cell and one type of bast cell1 so far as we know1 are not present4 ,these cells are the true vessels of the wood of flowering plants1 and the long bast cells with their companion proteid cells4 ,the figure of a metaxylem wood cell1 shown in fig4 #ca1 t1 shows the more primitive type of wood cell1 which has an oblique cross wall4 ,this type of wood cell is found in all the fossil trees1 and all the living plants except the flowering plants4 ,the vessel type1 which is that in the big wood vessels of the flowering plants1 and has no cross wall1 is seen in fig4 #bj1 x4 ,the similarity between the living cells and those of the ,coal ,measure fossils is sufficiently illustrated to need no further comment4 ,this similarity is an extremely helpful point when we come to an interpretation of the fossils4 ,in living plants we can study the physiology of the various kinds of cells1 and can deduce from experiment exactly the part they play in the economy of the whole plant4 ,from a study of the tissues in any plant structure we know what function it performed1 and can very often estimate the nature of the surrounding conditions under which the plant was growing4 ,to take a single example1 the palisade tissue1 illustrated in fig4 #be1 p1 in living plants always contains green colouring matter1 and lies just below the epidermis1 usually of leaves1 but sometimes also of green stems4 ,these cells do most of the starch manufacture for the plant1 and are found best developed when exposed to a good light4 ,in very shady places the leaves seldom have this type of cell4 ,now1 when cells just like these are found in fossils 7as is illustrated in fig4 #cd71 we can assume all the physiological facts mentioned above1 and rest assured that that leaf was growing under normal conditions of light and was actively engaged in starch-building when it was alive4 ,from the physiological standpoint the fossil leaf is entirely the same as a normal living one4 ,illustration3 ,fig4 #cd4--;,from a ,photo of a ,fossil ,lea e1 ,epidermis2 p1 palisade cells2 pr1 soft parenchyma cells 7poorly preserved72 s1 sclerenchyma above the vascular bundle4 ,from the morphological standpoint1 also1 the features of the plant body from the ,coal ,measure period fall into the same divisions as those of the present4 ,roots1 stems1 leaves1 and reproductive organs1 the essentially distinct parts of a plant1 are to be found in a form entirely recognizable1 or sufficiently like that now in vogue to be interpreted without great difficulty4 ,in the detailed structure of the reproductive organs more changes have taken place than in any others1 both in internal organization and external appearance4 ,already1 in the ,early ,palozoic period1 the distinction between leaves1 stems1 roots1 and reproductive organs was as clearly marked as it is to-day1 and1 judging by their structure1 they must each have performed the physiological functions they now do4 ,roots have changed least in the course of time1 probably because1 in the earth1 they live under comparatively uniform conditions in whatever period of the world's history they are growing4 ,naturally1 between the roots of different species there are slight differences2 but the likeness between fern roots from the ,palozoic and from a living fern is absolutely complete4 ,this is illustrated in fig4 #ce1 which shows the microscopic structure of the two roots when cut in transverse direction4 ,the various tissues will be recognized as coming into the table on p4 #ed1 so that both in the details of individual cells and in the general arrangement of the cell groups or tissues the roots of these fossil and living ferns agree4 ,illustration3 ,fig4 #ce4--;,a1 ,root of ,living ,fern4 ,b1 ,root of ,palozoic ,fossil ,fern4 c1 ,cortex2 px1 protoxylem in two groups2 m1 metaxylem2 s1 space in fossil due to decay of soft cells4 ,among stems there has been at all periods more variety than among the roots of the corresponding plants1 and in the following chapter1 when the differences between living and fossil plants will be considered1 there will be several important structures to notice4 ,nevertheless1 there are very many characters in which the stems from such widely different epochs agree4 ,the plants in the palozoic forests were of many kinds1 and among them were those with weak trailing stems which climbed over and supported themselves on other plants1 and also tall1 sturdy shafts of woody trees1 many of which were covered with a corky bark4 ,leaves were attached to the stems1 either directly1 as in the case of some living plants1 or by leaf stalks4 ,in external appearance and in general function the stems then were as stems are now4 ,in the details of the individual cells also the likeness is complete2 it is in the grouping of the cells1 the anatomy of the tissues1 that the important differences lie4 ,it has been remarked already that increase in complexity of the plant form usually goes with an increase in complexity of the cells and variety of the tissues4 ,the general ground tissue in nearly all plants is very similar2 it is principally in the vascular system that the advance and variety lie4 ,plant anatomists lay particular stress on the vascular system1 which1 in comparison with animal anatomy1 holds an even more important position than does the skeleton4 ,to understand the essential characters of stems1 both living and fossil1 and to appreciate their points of likeness or difference1 it is necessary to have some knowledge of the general facts of anatomy2 hence the main points on which stress is laid will be given now in brief outline4 ,leaving aside consideration of the more rudimentary and less defined structure of the alg and mosses1 all plants may be said to possess a 8vascular system04 ,this is typically composed of elongated wood 7or xylem7 with accessory cells 7see p4 #eg1 table71 and bast 7phloem71 also with accessory cells4 ,these specialized conducting elements lie in the ground tissue1 and in nearly all cases are cut off from direct contact with it by a definite sheath1 called the endodermis 7see p4 #ee1 fig4 #bf74 ,very often there are also groups or rings of hard thick-walled cells associated with the vascular tissues1 which protect them and play an important part in the consolidation of the whole stem4 ,illustration3 ,fig4 #cf4--;,diagram of ,simplest ,arrangement of ,complete ,stele in a ,stem ,w1 ,central solid wood2 ,p1 ring of bast2 ,e1 enclosing sheath of endodermis2 ,c1 ground tissue or cortex4 ,the simplest1 and probably evolutionally the most primitive form which is taken by the vascular tissues1 is that of a single central strand1 with the wood in the middle1 the bast round it1 and a circular endodermis enclosing all1 as in fig4 #cf1 which shows a diagram of this arrangement4 ,such a mass of wood and bast surrounded by an endodermis1 is technically known as a stele1 a very convenient term which is much used by anatomists4 ,in its simplest form 7as in fig4 #cf7 it is called a protostele1 and is to be found in both living and fossil plants4 ,a number of plants which get more complex steles later on1 have protosteles in the early stages of their development1 as in ,pteris aurita for example1 a species allied to the bracken fern1 which has a hollow ring stele when mature4 ,illustration3 ,fig4 #cg4--;,diagram of a ,stele with a few ,cells of ,pith p in the ,middle of the ,wood4 ,lettering as in fig4 #cf ,illustration3 ,fig4 #ch4--;,diagram showing ,extensive ,pith p in the ,wood4 ,lettering as in fig4 #cf ,the next type of stele is quite similar to the protostele1 but with the addition of a few large unspecialized cells in the middle of the wood 7p1 fig4 #cg72 these are the commencement of the hollowing process which goes on in the wood1 resulting later in the formation of a considerable pith1 as is seen in fig4 #ch1 where the wood is now a hollow cylinder1 as the phloem has been from the first4 ,when this is the case1 a second sheath or endodermis generally develops on the inner side of the wood1 outside the pith1 and cuts the vascular tissues off from the inner parenchyma4 ,a further step is the development of an inner cylinder of bast so that the vascular ring is completely double1 with endodermis on both sides of the cylinder1 as is seen in fig4 #ci4 ,illustration3 ,fig4 #ci4--;,a ,cylindrical ,stele1 with e1 inner endodermis1 and ph1 inner phloem2 ,w1 wood2 ,p1 outer phloem2 ,e1 outer endodermis4 ,l1 part of the stele going out to supply a large leaf1 thus breaking what would otherwise appear as a closed ring stele ,in all these cases there is but one strand or cylinder1 of vascular tissue in the stem1 but one stele1 and this type of anatomy is known as the monostelic or single-steled type4 ,illustration3 ,fig4 #dj4--;,a ,ring ,stele apparently broken up into a ,number of ,protosteles by many ,leaf ,gaps ,when from the double cylinder just described a strand of tissue goes off to supply a large leaf1 a considerable part of the stele goes out and breaks the ring4 ,this is shown in fig4 #ci1 where ,l is the part of the stele going to a leaf1 and the rest the broken central cylinder4 ,when the stem is short1 and leaves grow thickly so that bundles are constantly going out from the main cylinder1 this gets permanently broken1 and its appearance when cut across at any given point is that of a group of several steles arranged in a ring1 each separate stele being like the simple protostele in its structure4 ,see fig4 #dj4 ,this type of stem has long been known as polystelic 7i4e4 many-steled71 and it is still a convenient term to describe it by4 ,there has been much theoretical discussion about the true meaning of such a 8polystelic0 stem1 which cannot be entered into here2 it may be noted1 however1 that the various strands of the broken ring join up and form a meshwork when we consider the stem as a whole1 it is only in a single section that they appear as quite independent protosteles4 ,nevertheless1 as we generally consider the anatomy of stems in terms of single sections1 and as the descriptive word 8polystelic0 is a very convenient and widely understood term1 it will be used throughout the book when speaking of this type of stem anatomy4 ,such a type as this1 shown in fig4 #dj1 is already complex1 but it often happens that the steles branch and divide still further1 until there is a highly complicated and sometimes bewildering system of vascular strands running through the ground tissue in many directions1 but cut off from it by their protective endodermal sheaths4 ,such complex systems are to be found both in living and fossil plants1 more especially in many of the larger ferns 7see fig4 #hh74 ,higher plants in general1 however1 and in particular flowering plants1 do not have a polystelic vascular arrangement1 but a specialized type of monostele4 ,illustration3 ,fig4 #da4--,monostele in which the ,central ,pith is ,star-shaped1 and the ,wood breaking up into ,separate ,groups p1 ,pith2 ,w1 wood2 ,p1 phloem2 ,e1 endodermis2 ,c1 cortex4 ,referring again to fig4 #cg as a starting-point1 imagine the pith in the centre to spread in a star-shaped form till the points of the star touched the edges of the ring1 and thus to break the wood ring into groups4 ,a stage in this process 7which is not yet completed7 is shown in fig4 #da1 while in fig4 #db the wood and bast groups are entirely distinct4 ,in the flowering plants the cells of the endodermis are frequently poorly characterized1 and the pith cells resemble those of the cortical ground tissue1 so that the separate groups of wood and bast 7usually known as 8vascular bundles01 in distinction from the 8steles0 of fig4 #dj7 appear to lie independently in the ground tissue4 ,these strands1 however1 must not be confused with steles1 they are only fragments of the single apparently broken up stele which runs in the stem4 ,illustration3 ,fig4 #db4--,monostele in which the ,pith has invaded all the ,tissues as far as the ,endodermis1 and broken the ,wood and ,phloem up into ,separate ,bundles4 ,these are usually called 8vascular bundles0 in the flowering plants ,illustration3 ,fig4 #dc4--,showing actively growing ,zone c 7,cambium7 in the ,vascular ,bundles1 and joining across the ground tissue between them ,the vascular bundle1 of all except the ,monocotyledons1 has a potentiality for continued growth and expansion which places it far above the stele in value for a plant of long life and considerable growth4 ,the cells lying between the wood and the bast1 the soft parenchyma cells always accompanying such tissues1 retain their vitality and continue to divide with great regularity1 and to give rise to a continuous succession of new cells of wood on the one side and bast on the other2 see fig4 #cc1 c1 b4 ,in this way the primary1 distinct vascular bundles are joined by a ring of wood1 see fig4 #dc1 to which are added further rings every season1 till the mass of wood becomes a strong solid shaft4 ,this ever-recurring activity of the cambium gives rise to what are known as 8annual rings0 in stems1 see fig4 #dd1 in which the wood shows both primary distinct groups in the centre1 and the rings of growth of later years4 ,cambium with this power of long-continued activity is found in nearly all the higher plants of to-day 7except the ,monocotyledons71 but in the fern and lycopod groups it is in abeyance4 ,certain cases from nearly every family of the ,pteridophytes are known1 where some slight development of cambium with its secondary thickening takes place1 but in the groups below the ,gymnosperms cambium has almost no part to play4 ,on the other hand1 so far back as the ,carboniferous period1 the masses of wood in the ,pteridophyte trees were formed by cambium in just the same way as they are now in the higher forms4 ,its presence was almost universal at that time in the lower groups where to-day there are hardly any traces of it to be found4 ,illustration3 ,fig4 #dd4--,stem with ,solid ,cylinder of ,wood developed from the ,cambium1 showing three 8annual rings04 ,in the centre may still be seen the separate groups of the wood of the primary 8vascular bundles0 ,it will be seen from this short outline of the vascular system of plants1 that there is much variety possible from modifications of the fundamental protostele4 ,it is also to be noted that the plants of the ,coal ,measures had already evolved all the main varieties of steles which are known to us even now1#f and that the development of secondary thickening was very widespread4 ,in several cases the complexity of type exceeds that of modern plants 7see ,chap4 ,,vii71 and there are to be found vascular arrangements no longer extant4 ,when we turn to the ,reproductive ,organs1 we find that the points of likeness between the living and the fossil forms are not so numerous or so direct as they are in the case of the vegetative system4 ,illustration3 ,fig4 #de4--;,fern ,sporangia ,a1 fossil2 ,b1 living4 ,as has been indicated1 the families of plants typical of the ,coal ,measures were not those which are the most prominent to-day1 but belonged to the lower series of ,pteridophytes4 ,in their simpler forms the fructifications then and now resemble each other very closely1 but in the more elaborate developments the points of variety are more striking1 so that they will be dealt with in the following chapter4 ,cases of likeness are seen in the sporangia of ferns1 some of which appear to have been practically identical with those now living4 ,this is illustrated in fig4 #de1 which shows the outline of the cells of the sporangia of living and fossil side by side4 ,illustration3 ,fig4 #df4--;,a1 ,living ,lycopod cone2 ,b1 ,lepidodendron 7fossil7 cone4 a1 ,axis2 s1 scale2 ,s1 sporangium with spores4 ,one side of a longitudinal section ,in the general structure also of the cones of the simpler types of ,lepidodendron 7fossil1 see frontispiece7 there is a close agreement with the living ,lycopods1 though as regards size and output of spores there was a considerable difference in favour of the fossils4 ,the plan of each is that round the axis of the cone simple scales are arranged1 on each of which1 on its upper side1 is seated a large sporangium bearing numerous spores all of one kind 7see fig4 #df74 ,equally similar are the cones of the living ,equisetum and some of the simple members of the fossil family ,calamite1 but the more interesting cases are those where differences of an important morphological nature are to be seen4 ,as regards the second#g generation there is some very important evidence1 from extremely young stages1 which has recently been given to the world4 ,in a fern sporangium germinating spores were fossilized so as to show the first divisions of the spore cell4 ,these seem to be identical with the first divisions of some recent ferns 7see fig4 #dg74 ,this is not only of interest as showing the close similarity in detail between plants of such widely different ages1 but is a remarkable case of delicate preservation of soft and most perishable structures in the 8coal balls04 ,illustration3 ,fig4 #dg4--;,germinating ,fern ,spores ,a and ,b1 from carboniferous fossils2 ,c1 living fern4 7,a and ,b after ,scott47 ,while these few cases illustrate points of likeness between the fructifications of the ,coal ,measures and of to-day1 the large size and successful character of the primitive ,coal ,measure plants was accompanied by many developments on the part of their reproductive organs which are no longer seen in living forms1 and the greater number of palozoic fructifications must be considered in the next chapter4 ,,chapter ,,vii ,,minute ,,structure ,,of ,,fossil ,,plants--,,differences ,,from ,,living ,,ones ,we have seen in the last chapter that the main morphological divisions1 roots1 stems1 leaves1 and fructifications1 were as distinct in the ,coal ,measure period as they are now4 ,there is one structure1 however1 found in the ,coal ,measure fossils1 which is hardly paralleled by anything similar in the living plants1 and that is the fossil known as ,stigmaria4 ,stigmaria is the name given1 not to a distinct species of plant1 but to the large rootlike organs which we know to have belonged to all the species of ,lepidodendron and of ,sigillaria4 ,in the frontispiece these organs are well seen1 and branch away at the foot of the trunk1 spreading horizontally1 to all appearance merely large roots4 ,they are especially regularly developed1 however1 the main trunk giving rise always to four primary branches1 these each dividing into two equal branches1 and so on--in this they are unlike the usual roots of trees4 ,they bore numerous rootlets1 of which we know the structure very well1 as they are the commonest of all fossils1 but in their internal anatomy the main 8roots0 had not the structure which is characteristic of roots1 but were like stems4 ,in living plants there are many examples of stems which run underground1 but they always have at least the rudiments of leaves in the form of scales1 while the fossil structures have apparently no trace of even the smallest scales1 but bear only rootlets1 thus resembling true roots4 ,the questions of morphology these structures raise are too complex to be discussed here1 and ,stigmaria is only introduced as an example1 one of the very few available1 of a palozoic structure which seems to be of a nature not clearly determinable as either root1 stem1 leaf1 or fructification4 ,among living plants the fine rootlike rhizophores of ,selaginella bear some resemblance to ,stigmaria in essentials1 though so widely different from them in many ways1 and they are probably the closest analogy to be found among the plants of to-day4 ,the individual cells1 we have already seen1 are strikingly similar in the case of fossil and living plants4 ,there are1 of course1 specific varieties peculiar to the fossils1 of which perhaps the most striking seem to be some forms of hair cells4 ,for example1 in a species of fern from the ,french rocks there were multicellular hairs which looked like little stems of ,equisetum owing to regular bands of teeth at the junctions of the cells4 ,these hairs were quite characteristic of the species--but hairs of all sorts have always abounded in variety1 so that such distinction has but minor significance4 ,illustration3 ,fig4 #dh4--,stele of ,lepidodendron ,w1 surrounded by a small ring of secondary wood ,s ,as was noted in the table 7p4 #eh7 the only cell types of prime importance which were not evolved by the ,palozoic plants were the wood vessels1 phloem and accompanying cells which are characteristic of the flowering plants4 ,among the fossils the vascular arrangements are most interesting1 and1 as well as all the types of stele development noted in the previous chapter as common to both living and fossil plants1 there are further varieties found only among the fossils 7see fig4 #ej74 ,the simple protostele described 7on p4 #fa7 is still found1 particularly in the very young stages of living ferns1 but it is a type of vascular arrangement which is not common in the mature plants of the present day4 ,in the ,coal ,measure period1 however1 the protostele was characteristic of one of the two main groups of ferns4 ,in different species of these ferns1 the protostele assumed a large variety of shapes and forms as well as the simple cylindrical type4 ,the central mass of wood became five-rayed in some1 star-shaped1 and even very deeply lobed1 with slightly irregular arms1 but in all these cases it remained fundamentally monostelic4 ,frequently secondary tissue developed round the protosteles of plants whose living relatives have no such tissue4 ,a case of this kind is illustrated in fig4 #dh1 which shows a simple circular stele surrounded by a zone of secondary woody tissue in a species of ,lepidodendron4 ,illustration3 ,fig4 #di4--,lepidodendron1 showing ,part of the ,hollow ,ring of ,primary ,wood ,w1 with a relatively large amount of ,secondary ,tissue ,s1 surrounding it ,in many species of ,lepidodendron the quantity of secondary wood formed round the primary stele was very great1 so that 7as is the case in higher plants7 the primary wood became relatively insignificant compared with it4 ,in most species of ,lepidodendron the primary stele is a hollow ring of wood 7cf4 fig4 #ch1 p4 #fb7 round which the secondary wood developed1 as is seen in fig4 #di4 ,these two cases illustrate a peculiarity of fossil plants4 ,among living ones the solid and the simple ring stele are almost confined to the ,pteridophytes1 where secondary wood does not develop1 but the palozoic ,pteridophytes1 while having the simple primary types of steles1 had quantities of secondary tissue1 which was correlated with their large size and dominant position4 ,illustration3 ,fig4 #ej4--;,diagram of ,steles of the ,english ,medullosa1 showing three irregular1 solid1 steles ,a1 with secondary thickenings ,s1 all round each4 a1 ,small accessory steles ,among polystelic types 7see p4 #fc7 we find interesting examples in the fossil group of the ,medullose1 which are much more complex than any known at present1 both owing to their primary structure and also to the peculiar fact that all the steles developed secondary tissue towards the inner as well as the outer side4 ,one of the simpler members of this family found in the ,english ,coal ,measures is illustrated in fig4 #ej4 ,here there are three principal protosteles 7and several irregular minor ones7 each of which has a considerable quantity of secondary tissue all round it1 so that a portion of the secondary wood is growing in towards the actual centre of the stem as a whole--a very anomalous state of affairs4 ,in the more complex ,continental type of ,medullosa there are very large numbers of steles4 ,in the one figured from the ,continent in fig4 #ea but a few are represented4 ,there is a large outer double-ring stele1 with secondary wood on both sides of it1 and within these a number of small steles1 all scattered through the ground tissue1 and each surrounded by secondary wood4 ,in actual specimens the number of these central steles is much greater than that indicated in the diagram4 ,no plant exists to-day which has such an arrangement of its vascular cylinder4 ,it almost appears as though at the early period1 when the ,medullose flourished1 steles were experimenting in various directions4 ,such types as are illustrated in figs4 #ej and #ea are obviously wasteful 7for secondary wood developing towards the centre of a stem is bound to finally meet71 and complex1 but apparently inefficient1 which may partly account for the fact that this type of structure has not survived to the present1 though simpler and equally ancient types have done so4 ,illustration3 ,fig4 #ea4--;,continental ,medullosa1 showing ,r1 outer double-ring stele with secondary wood all round it2 ,s1 inner stellate steles1 also surrounded in each case by secondary tissue ,further details of the anatomy of fossils will be mentioned when we come to consider the individual families2 those now illustrated suffice to show that in the ,coal ,measures very different arrangements of steles were to be found1 as well as those which were similar to those existing now4 ,the significance of these differences will become apparent when their relation to the other characters of the plants is considered4 ,the fructifications1 always the most important parts of the plant1 offer a wide field1 and the divergence between the commoner palozoic and recent types seems at first to be very great4 ,indeed1 when palozoic reproductive bodies have to be described1 it is often necessary to use the common descriptive terms in an altered and wider sense4 ,among the plants of to-day there are many varieties of the simple single-celled reproductive masses which are called spores1 and which are usually formed in large numbers inside a spore case or sporangium4 ,among the higher plants seeds are also known in endless variety1 all of which1 compared with spores1 are very complex1 for they are many-celled structures1 consisting essentially of an embryo or young plant enclosed in various protective coats4 ,the distinction between the two is sharp and well defined1 and for the student of living plants there exists no difficulty in separating and describing seeds and spores4 ,but when we look back through the past eras to palozoic plants the subject is not so easy1 and the two main types of potentially reproductive masses are not sharply distinct4 ,the seed1 as we know it among recent plants1 and as it is generally defined1 had not fully evolved2 while the spores were of great variety and had evolved in several directions1 some of which seem to have been intermediate stages between simple spores and true seeds4 ,these seedlike spores served to reproduce the plants of the period1 but their type has since died out and left but two main methods among living plants1 namely the essentially simple spores1 the very simplicity of whose organization gives them a secure position1 and the complex seeds with their infinite variety of methods for protecting and scattering the young embryos they contain4 ,among the ,coal ,measure fossils we can pick up some of the early stages in the evolution of the seed from the spore1 or at least we can examine intermediate stages between them which give some idea of the possible course of events4 ,hence1 though the differences from our modern reproductive structures are so noticeable a feature of the palozoic ones1 it will be seen that they are really such differences as exist between the members at the two ends of a series1 not such as exist between unrelated objects4 ,very few types can be mentioned here1 and to make their relations clear a short series of diagrams with explanations will be found more helpful than a detailed account of the structures4 ,illustration3 ,fig4 #eb4--,spores ,each spore a single cell which develops with three others in tetrads 7groups of four74 ,very numerous tetrads enclosed in a spore case or sporangium which develops on a leaflike segment called the sporophyll4 ,each spore germinates independently of the others after being scattered1 all being of the same size4 ,common in fossils and living ,pteridophytes4 ,illustration3 ,fig4 #ec4--,spores ,each a single cell like the preceding1 but here only one tetrad in a sporangium ripens1 so that each contains only four spores4 ,compared with the preceding types these spores are very large4 ,otherwise details similar to above4 ,some fossils have such sporangia with eight spores1 or some other small number2 living ,selaginellas have four4 ,in the same cone sporangia with small spores are developed and give rise to the male organs4 ,illustration3 ,fig4 #ed4--8,spores0 of ,seedlike ,structure ,out of a tetrad in each sporangium only one spore ripens1 ,s in figure1 the others1 s1 abort4 ,the wall of the sporangium1 w1 is more massive than in the preceding cases1 and from the sporophyll1 flaps1 sp f1 grow up on each side and enclose and protect the sporangium4 ,the one big spore appears to germinate inside these protective coats1 and not to be scattered separately from them4 ,only found in fossils1 one of the methods of reproduction in ,lepidodendron4 ,other sporangia with small spores were developed which gave rise to the male organs4 ,illustration3 ,fig4 #ee4--8,seed0 ,in appearance this is like a seed1 but differs from a true seed in having no embryo1 and is like the preceding structure in having a very large spore1 ,s1 though there is no trace of the three aborting ones4 ,the spore develops in a special mass of tissue known as the nucellus1 n1 which partly corresponds to the sporangium wall of the previous types4 ,in it a cavity1 p c1 the pollen chamber1 receives the pollen grains which enter at the apex of the 8seed04 ,there is a complex coat1 ,c1 which stands round the nucellus but is not joined to it1 leaving the space l between them4 ,only in fossils2 ,trigonocarpus 7see p4 #abb7 is similarly organized4 ,small spores in fern-like sporangia1 called pollen grains4 ,illustration3 ,fig4 #ef4--8,seed0 ,very similarly organized to the above1 but the coat is joined to the nucellus about two-thirds of its extent1 and up to the level l4 ,in the pollen chamber1 p c1 a cone of nucellar tissue projects1 and the upper part of the coat is fluted1 but these complexities are not of primary importance4 ,the large spore ,s germinated and was fertilized within the 8seed01 but apparently produced no embryo before it ripened4 ,small 8spores0 in fern-like sporangia form the pollen grains4 ,only in fossils1 e4g4 ,lagenostoma4 7,see p4 #aai47 ,illustration3 ,fig4 #eg4--,seed ,essentially similar to the preceding1 except in the possession of an embryo e1 which is1 however1 small in comparison with the endosperm which fills the spore ,s4 ,the whole organization is simpler than in the fossil ,lagenostoma1 but the coat is fused to the nucellus further up 7see l74 ,small 8spores0 form the pollen grains4 ,living and fossil type1 ,cycads and ,ginkgo4 ,illustration3 ,fig4 #eh4--,seed ,in the ripe seed the large embryo e practically fills up all the space within the two seed coats c#a and c#b2 endosperm1 pollen chamber1 c41 have been eliminated1 and the young ovule is very simple and small as a result of the protection and active service of the carpels in which it is enclosed4 ,small 8spores0 form the pollen grains4 ,typical of living ,dicotyledons4 ,these few illustrations represent only the main divisions of an army of structures with an almost unimaginable wealth of variety which must be left out of consideration4 ,for the structures illustrated in figs4 #ed1 #ee1 and #ef we have no name1 for their possible existence was not conceived of when our terminology was invented1 and no one has yet christened them anew with distinct names4 ,they are evidently too complex in organization and too similar to seeds in several ways to be called spores1 yet they lack the essential element in a seed1 namely1 an embryo4 ,the term 8ovule0 7usually given to the young seed which has not yet developed an embryo7 does not fit them any better1 for their tissues are ripened and hard1 and they were of large size and apparently fully grown and mature4 ,for the present a name is not essential2 the one thing that is important is to recognize their intermediate character and the light they throw on the possible evolution of modern seeds4 ,a further point of great interest is the manner in which these 8seeds0 were borne on the plant4 ,to-day seeds are always developed 7with the exception of ,cycas7 in cones or flowers1 or at least special inflorescences4 ,but the 8seed0 of ,lagenostoma 7fig4 #ef71 as well as a number of others in the group it represents1 were not borne on a special structure1 but directly on the green foliage leaves4 ,they were in this on a level with the simple sporangia of ferns which appear on the backs of the fronds1 a fact which is of great significance both for our views on the evolution of seeds as such1 and for the bearing it has on the relationships of the various groups of allied plants4 ,this will be referred to subsequently 7,chapter ,,xi71 and is mentioned now only as an example of the difference between some of the characters of early fossils and those of the present day4 ,it is true that botanists have long recognized the organ which bears seeds as a modified leaf4 ,the carpels of all the higher plants are looked on as homologous with leaves1 although they do not appear to be like them externally4 ,sometimes among living plants curious diseases cause the carpels to become foliar1 and when this happens the diseased carpel reverts more or less to the supposed ancestral leaf-like condition4 ,it is only among the ancient 7but recently discovered7 fossils1 however1 that seeds are known to be borne normally on foliage leaves4 ,from ,mesozoic plants we shall learn new conceptions about flowers and reproductive inflorescences in general1 but these must be deferred to the consideration of the family as a whole 7,chapter ,,xiii74 ,enough has been illustrated to show that though the individual cells1 the bricks1 so to speak1 of plant construction1 were so similar in the past and present1 yet the organs built up by them have been continually varying1 as a child builds increasingly ambitious palaces with the same set of bricks4 ,,chapter ,,viii ,,past ,,histories ,,of ,,plant ,,families ,i4 ,flowering ,plants1 ,angiosperms ,in comparison with the other groups of plants the flowering families are of recent origin1 yet in the sense in which the word is usually used they are ancient indeed1 and the earliest records of them must date at least to periods hundreds of thousands of years ago4 ,through all the ,tertiary period 7see p4 #cd7 there were numerous flowering plants1 and there is evidence that many families of both ,monocotyledons and ,dicotyledons existed in the ,upper ,cretaceous times4 ,further back than this we have little reliable testimony1 for the few specimens of so-called flowering plants from the ,lower ,mesozoic are for the most part of a doubtful nature4 ,the flowering plants seem to stand much isolated from the rest of the plant world2 there is no direct evidence of connection between their oldest representatives and any of the more primitive families4 ,so far as our actual knowledge goes1 they might have sprung into being at the middle of the ,mesozoic period quite independently of the other plants then living2 though there are not wanting elaborate and almost convincing theories of their connection with more than one group of their predecessors 7see p4 #ajh74 ,it is a peculiarly unfortunate fact that although the rocks of the ,cretaceous and ,tertiary are so much less ancient than those of the ,coal ,measures1 they have preserved for us far less well the plants which were living when they were formed4 ,hitherto no one has found in ,mesozoic strata masses of exquisitely mineralized ,angiosperm fragments#h like those found in the ,coal ,measures1 which tell us so much about the more ancient plants4 ,cases are known of more or less isolated fragments with their microscopical tissues mineralized4 ,for example1 there are some palms and ferns from ,south ,america which show their anatomical structure very clearly preserved in silica1 and which seem to resemble closely the living species of their genera4 ,the bulk of the plants preserved from these periods are found in the form of casts or impressions 7see p4 #aj71 which1 as has been pointed out already1 are much less satisfactory to deal with1 and give much less reliable results than specimens which have also their internal structure petrified4 ,the quantity of material1 however1 is great1 and impressions of single leaves innumerable1 and of specimens of leaves attached to stems1 and even of flowers and fruits1 are to be found in the later beds of rock4 ,these are generally clearly recognizable as belonging to one or other of the living families of flowering plants4 ,leaf impressions are by far the most frequent1 and our knowledge of the ,tertiary flora is principally derived from a study of them4 ,their outline and their veins are generally preserved1 often also their petioles and some indication of the thickness and character of the fleshy part of the leaf4 ,from the outline and veins alone an expert is generally able to determine the species to which the plant belongs1 though it is not always quite safe to trust to these determinations or to draw wide-reaching conclusions from them4 ,in fig4 #ei is shown a photograph of the impression of a ,tertiary leaf1 which illustrates the condition of an average good specimen from rocks of the period4 ,its shape and the character of the veins are sufficient to mark it out immediately as belonging to the ,dicotyledonous group of the flowering plants4 ,seeds and fruits are also to be found2 and in some very finely preserved specimens from ,japan stamens from a flower and delicate seeds are seen clearly impressed on the light stone4 ,in fig4 #fj is illustrated a couple of such seeds1 which show not only their wings but also the small antenn-like stigmas4 ,specimens so perfectly preserved are practically as good as herbarium material of recent plants1 and in this way the externals of the ,tertiary plants are pretty well known to us4 ,illustration3 ,fig4 #ei4--;,dicotyledonous ,leaf ,impression from ,tertiary ,rocks ,illustration3 ,fig4 #fj4--,seeds from ,japanese ,tertiary ,rocks2 at a are seen the two stigmas still preserved ,a problem which has long been discussed1 and which has aroused much interest1 is the relative antiquity of the ,monocotyledonous and the ,dicotyledonous branches of the flowering plants4 ,a peculiar fascination seems to hang over this still unsolved riddle1 and a battle of flowers may be said to rage between the lily and the rose for priority4 ,recent work has thrown no decisive light on the question1 but it has undoubtedly demolished the old view which supposed that the ,monocotyledons 7the lily group7 appeared at a far earlier date upon this earth than the ,dicotyledons4 ,the old writers based their contention on incorrectly determined fossils4 ,for instance1 seeds from the ,palozoic rocks were described as ,monocotyledons because of the three or six ribs which were so characteristic of their shell2 we know now that these seeds 7,trigonocarpus7 belong to a family already mentioned in another connection 7p4 #gb71 the ,medullose 7see p4 #abb71 the affinity of which lies between the cycads and the ferns4 ,leaves of ,cordaites1 again1 which are broad and long with well-marked parallel veins1 were described as those of a ,monocotyledonous plant like the ,yucca of to-day2 but we now know them to belong to a family of true ,gymnosperms possibly distantly related to ,taxus 7the ,yew tree74 ,recent work1 which has carefully sifted the fossil evidence1 can only say that no true ,monocotyledons have yet been found below the ,lower ,cretaceous rocks1 and that at that period we see also the sudden inrush of ,dicotyledons4 ,hence1 so far as palontology can show1 the two parallel groups of the flowering plants arose about the same time4 ,it is of interest to note1 however1 that the only petrifaction of a flower known from any part of the world is an ovary which seems to be that of one of the ,liliace4 ,in the same nodules1 however1 there are several specimens of ,dicotyledonous woods1 so that it does not throw any light on the question of priority4 ,with the evidence derived from the comparative study of the anatomy of recent flowering plants we cannot concern ourselves here1 beyond noting that the results weigh in favour of the ,dicotyledons as being the more primitive1 though not necessarily developed much earlier in point of time4 ,until very much more is discovered than is yet known of the origin of the flowering plants as a whole1 it is impossible to come to a more definite conclusion about this much-discussed subject4 ,let us now attempt to picture the vegetable communities since the appearance of the flowering plants4 ,the facts which form the bases of the following conceptions have been gathered from many lands by numerous workers in the field of fossil botany1 from scattered plant remains such as have been described4 ,when the flowering plants were heralded in they appeared in large numbers1 and already by the ,cretaceous period there were very many different species4 ,of these a number seem to belong to genera which are still living1 and many of them are extremely like living species4 ,it would be wearisome and of little value to give a list of all the recorded species from this period1 but a few of the commoner ones may be mentioned to illustrate the nature of the plants then flourishing4 ,several species of ,quercus 7the ,oak7 appeared early1 particularly ,quercus ,ilex2 leaves of the ,juglandace 7,walnut family7 were very common1 and among the ,tertiary fossils appear its fruits4 ,both ,populus 7the ,poplar7 and ,salix 7the ,willow7 date from the early rocks1 while ,ficus 7the ,fig7 was very common1 and ,casuarina 7the ,switch ,plant7 seems to have been widely spread4 ,magnolias also were common1 and it appears that ,platanus 7the ,plane7 and ,eucalyptus coexisted with them4 ,it will be immediately recognized that the above plants have all living representatives1 either wild or cultivated1 growing in this country at the present day1 so that they are more or less familiar objects1 and there appears to have been no striking difference between the early flowering plants and those of the present day4 ,between the ancient ,lycopods1 for example1 and those now living the differences are very noteworthy2 but the earliest of the known flowering plants seem to have been essentially like those now flourishing4 ,it must be remembered in this connection that the existing flowering plants are immensely nearer in point of time to their origin than are the existing ,lycopods1 and that when such ons have passed as divide the present from the ,palozoic1 the flowering plants of the future may have dwindled to a subordinate position corresponding to that held by the ,lycopods now4 ,a noticeable character of the early flowering-plant flora1 when taken as a whole1 is the relatively large proportion of plants in it which belong to the family ,amentifer 7oaks1 willows1 poplars1 c474 ,this is supposed by some to indicate that the family is one of the most primitive stocks of the ,angiosperms4 ,this view1 however1 hardly bears very close scrutiny1 because it derives its main support from the large numbers of the ,amentifer as compared with other groups4 ,now1 the ,amentifer were 7and are7 largely woody resistant plants1 whose very nature would render them more liable to be preserved as impressions than delicate trees or herbs1 which would more readily decay and leave no trace4 ,similarly based on uncertain evidence is the surmise that the group of flowers classed as ,gamopetal 7flowers with petals joined up in a tube1 like convolvulus7 did not flourish in early times1 but are the higher and later development of the flower type4 ,now1 ,viburnum 7allied to the honeysuckle7 belongs to this group1 and it is found right down in the ,cretaceous1 and ,sambucus 7,elder1 of the same family7 is known in the early ,tertiary4 ,these two plants are woody shrubs or small trees1 while many others of the family are herbs1 and it is noteworthy that it is just these woody1 resistant forms which are preserved as fossils2 their presence demonstrates the antiquity of the group as a whole1 and the absence of other members of it may be reasonably attributed to accidents of preservation4 ,in the ,tertiary also we get a member of the heath family1 viz4 ,andromeda1 and another tube-flower1 ,bignonia1 as well as several more woody gamopetalous flowers4 ,hence it is wise to be very cautious about drawing any important conclusions from the relative numbers of the different species1 or the absence of any type of plant from the lists of those as yet known from the ,cretaceous4 ,when quantities of structurally preserved material can be examined containing the flowering plants in petrifactions1 then it will be possible to speak with some security of the nature of the ,mesozoic flora as a whole4 ,the positive evidence which is already accumulated1 however1 is of great value1 and from it certain deductions may be safely made4 ,specimens of ,cretaceous plants from various parts of the world seem to indicate that there was a very striking uniformity in the flora of that period all over the globe4 ,in ,america and in ,central ,europe1 for example1 the same types of plants were growing4 ,we shall see that1 as time advanced1 the various types became separated out1 dying away in different places1 until each great continent and division of land had a special set of plants of its own4 ,at the commencement of the reign of flowering plants1 however1 they seem to have lived together in the way we are told the beasts first lived in the garden of ,eden4 ,at the beginning of the ,tertiary period there were still many tropical forms1 such as ,palms1 ,cycads1 ,nipa1 various ,artocarpace1 ,laurace1 ,araliace1 and others1 growing side by side with such temperate forms as ,quercus1 ,alnus1 ,betula1 ,populus1 ,viburnum1 and others of the same kind4 ,before the middle of the ,tertiary was reached the last ,cycads died in what is now known as ,europe2 and soon after the middle ,tertiary all the tropical types died out of this zone4 ,at the same time those plants whose leaves appear to have fallen at the end of the warm season began to become common1 which is taken as an indication of a climatic influence at work4 ,some writers consider that in the ,cretaceous times there was no cold season1 and therefore no regular period of leaf fall1 but as the climate became temperate the deciduous trees increased in numbers2 yet the ,gymnospermic and ,angiospermic woods which are found with petrified structure show well-marked annual rings and seem to contradict this view4 ,toward the end of the ,tertiary times there were practically no more tropical forms in the ,european flora1 though there still remained a number of plants which are now found either only in ,america or only in ,asia4 ,the ,glacial epoch at the close of the ,tertiary appears to have driven all the plants before it1 and afterwards1 when its glaciers retreated1 shrinking up to the ,north and up the sides of the high mountains1 the plant species that returned to take possession of the land in the ,quaternary or present period were those which are still inhabiting it1 and the floras of the tropics1 ,asia1 and ,america were no longer mixed with that of ,europe4#i ,,chapter ,,ix ,,past ,,histories ,,of ,,plant ,,families ,,ii4 ,higher ,gymnosperms ,the more recent history of the higher ,gymnosperms1 in the ,upper ,cretaceous and ,tertiary periods1 much resembles that of the flowering plants as sketched in the previous chapter4 ,many of the genera appear to have been those still living1 and some of the species even may have come very close to or have been identical with those of to-day4 ,the forms now characteristic of the different continents were growing together1 and appear to have been widely distributed over the globe4 ,for example1 ,sequoia and ,taxodium1 two types now characteristic of ,america1 and ,glyptostrobus1 at present found in ,asia1 were still growing with the other ,european types in ,europe so late as middle ,tertiary times4 ,as in the case of the ,angiosperms1 the fossils we have of ,cretaceous and ,tertiary ,gymnosperms are nearly all impressions and casts1 though some more or less isolated stems have their structure preserved4 ,hence our knowledge of these later ,gymnosperms is far from complete4 ,from the older rocks1 however1 we have both impressions and microscopically preserved material1 and are more fully acquainted with them than with those which lived nearer our own time4 ,hard1 resistant leaves1 which are so characteristic of most of the living genera of ,gymnosperms1 seem to have been also developed in the past members of the group1 and these tend to leave clear impressions in the rocks1 so that we have reliable data for reconstructing the external appearance of the fossil forms from the ,palozoic period4 ,the resinous character of ,gymnosperm wood probably greatly assisted its preservation1 and fragments of it are very common in rocks of all ages1 generally preserved in silica so as to show microscopic structure4 ,the isolated wood of ,gymnosperms1 however1 is not very instructive1 for from the wood alone 7and usually it is just fragments of the secondary wood which are preserved7 but little of either physiological or evolutional value can be learned4 ,when twigs with primary tissues and bark and leaves attached are preserved1 then the specimens are of importance1 for their true character can be recognized4 ,fortunately among the coal balls there are many such fragments1 some of which are accompanied by fruits and male cones1 so that we know much of the ,palozoic ,gymnosperms1 and find that in some respects they differ widely from those now living4 ,there is1 therefore1 much more to be said about the fossil ,gymnosperms than about the ,angiosperms1 both because of the better quality of their preservation and because their history dates back to a very much earlier period than does the ,angiospermic record4 ,indeed1 we do not know when the ,gymnosperms began2 the well-developed and ancient group of ,cordaite was flourishing before the ,carboniferous period1 and must therefore date back to the rocks of which we have no reliable information from this point of view1 and the origin of the ,gymnosperms must lie in the pre-,carboniferous period4 ,the group of ,gymnosperms includes a number of genera of different types1 most of which may be arranged under seven principal families4 ,in a sketch of this nature it is1 of course1 quite impossible to deal with all the less-important families and genera4 ,those that will be considered here are the following3-- ,coniferales 7see p4 #ij74 ,araucare1 e4g4 ,monkey-puzzle ,genera both living and fossil4 ,fossil forms undoubted so far back as the ,jurassic1 and presumably further4 ,abietine1 e4g4 ,pine and ,larch ,genera both living and fossil4 ,fossils recognized as far back as the ,lower ,cretaceous4 ,cupresse1 e4g4 ,juniper1 ,cypress ,genera both living and fossil4 ,fossils recognized as far back as the ,jurassic4 ,taxe1 e4g4 ,yew ,genera living and fossil4 ,fossils recognized as far back as the ,cretaceous4 ,cordaitales 7see p4 #ib74 ,cordaite1 e4g4 ,cordaites ,fossil only4 ,characteristic of ,devonian1 ,carboniferous1 and ,permian periods4 ,poroxyle1 e4g4 ,poroxylon ,fossil only4 ,characteristic of the ,carboniferous and ,permian4 ,ginkgoales 7see p4 #ih74 ,ginkgoace1 e4g4 ,ginkgo ,fossil and living1 dating back1 apparently with little change1 to ,palozoic times4 ,we must pay the most attention to the two last groups1 as they are so important as fossils1 and the ,cordaite were a very numerous family in ,coal ,measure times4 ,they had their period of principal development so long ago that it is probable that no direct descendants remain to the present time1 though some botanists consider that the ,taxe are allied to them4 ,of the groups still living it is difficult1 almost impossible1 to say which is the highest1 the most evolved type4 ,in the consideration of the ,gymnosperm family it is brought home with great emphasis how incomplete and partial our knowledge is as yet4 ,many hold that the ,araucare are the most primitive of the higher ,gymnosperms4 ,in support of this view the following facts are noted4 ,they have a simple type of fructification1 with a single seed on a simple scale1 and many scales arranged round an axis to form a cone4 ,in the microscopic structure of their wood they have double rows of bordered pits1 a kind of wood cell which comes closer to the old fossil types than does the wood of any of the other living genera4 ,further than this1 wood which is almost indistinguishable from the wood of recent ,araucarias is found very far back in the rocks1 while their leaves are broad and simple1 and attached directly to the stem in a way similar to the leaves of the fossil ,cordaite1 and very different from the needle leaves on the secondary stems of the ,pine family2 so that there appears good ground for considering the group an ancient and probably a primitive one4#aj ,on the other hand1 there are not wanting scientists who consider the ,abietine the living representatives of the most primitive and ancient stock1 though on the whole the evidence seems to indicate more clearly that the ,pine-tree group is specialized and highly modified4 ,their double series of foliage leaves1 their complex cones 7whose structures are not yet fully understood71 and their wood all support the latter view4 ,some1 again1 consider the ,taxe as a very primitive group1 and would place them near the ,cordaite1 with which they may be related4 ,their fleshy seeds1 growing not in cones but on short special axes1 support this view1 and it is certainly true that in many ways the large seeds1 with their succulent coats and big endosperm1 are much like those of the lower ,gymnosperms and of several fossil types4 ,those1 however1 who hold to the view that the ,abietine are primitive1 see in the ,taxe the latest and most modified type of ,gymnosperm4 ,it will be seen from this that there is no lack of variety regarding the interpretation of ,gymnosperm structures4 ,the ,gymnosperms do not stand in such an isolated position as do the ,angiosperms4 ,whatever the variety of views held about the details of the relative placing of the families within the group1 all agree in recognizing the evidence which enables us to trace with confidence the connection between the lower ,gymnosperms and the families of ferns4 ,there are many indications of the intimate connection between higher and lower ,gymnosperms4 ,between the series exist what might be described as different degrees of cousinship1 and in the lower groups lie unmistakable clues to their connection with more ancient groups in the past which bridge over the gaps between them and the ferns4 ,for the present1 however1 let us confine ourselves to the history of the more important ,gymnosperms1 the discussion of their origin and the groups from which they may have arisen must be postponed until the necessary details about those groups have been mentioned4 ,to a consideration of the living families of ,araucare1 ,abietine1 ,cupresse1 and ,taxe we can allow but a short space2 their general characters and appearance are likely to be known to the reader1 and their details can be studied from living specimens if they are not4 ,for purposes of comparison with the fossils1 however1 it will be necessary to mention a few of the principal features which are of special importance in discussing phylogeny4 ,the ,araucariace are woody trees which attain a considerable size1 with broad-based1 large leaves attached directly to the stem4 ,in the leaves are a series of numerous parallel vascular bundles4 ,the wood cells in microscopic section show two rows or more of round bordered pits4 ,the cones are very large1 but the male and female are different in size and organization4 ,the female cone is composed of series of simple scales arranged spirally round the axis1 and each scale bears a single seed and a small ligule4 ,the pollen grains from the male cone are caught on the ligule and the pollen tubes enter the micropyle of the ovule1 bringing in passive male cells which may develop in large numbers in each grain4 ,the seeds when ripe are stony1 and some are provided with a wing from part of the tissue of the scale4 ,in the ripe cones the scales separate from the cone axis4 ,the ,abietine are woody trees1 some reaching a great height1 all with a strong main stem4 ,the leaves are of two kinds3 primary ones borne directly attached to the stem 7as in first-year shoots of the ,larch71 and secondary ones borne in tufts of two 7in ,pine7 or a large number 7in older branches of ,larch7 on special short branches1 the primary leaves only developing as brown scales closely attached to the stems4 ,leaves generally very fine and needlelike1 and with a central vascular bundle4 ,the wood in microscopic section shows a single row of round bordered pits on the narrow trache4 ,the female cones are large1 male and female differing greatly in size and organization4 ,the female cone1 composed of a spiral series of pairs of scales1 which often fuse together as the cone ripens4 ,each upper scale of the pair bears two seeds4 ,the pollen grains from the male cone enter the micropyle of the seed and are caught in the tissue 7apex of nucellus7 there2 the pollen tubes discharge passive male cells1 only two of which develop in each grain4 ,the seeds when ripe are stony and provided with a wing from the tissue of the scale on which they were borne4 ,the ,cupresse are woody trees reaching no great height1 and of a bushy1 branching growth4 ,the leaves are attached directly to the main stem1 and arrange themselves in alternating pairs of very small leaves1 closely pressed to the stem4 ,the wood in microscopic section shows a single row of round bordered pits on the trache4 ,the cones are small1 and the scales forming them arranged in cycles4 ,the female scales bear a varying number of seeds4 ,the pollen grain has two passive male cells4 ,the seeds when ripe are stony1 with wings1 though in some cases 7species of ,juniper7 the cone scales close up and become fleshy1 so that the whole fruit resembles a berry4 ,the ,taxe are woody1 though not great trees1 bushily branched4 ,the leaves are attached spirally all round the stem1 but place themselves so as to appear to lie in pairs arranged in one horizontal direction4 ,the wood in microscopic section shows a single row of round bordered pits on the trache4 ,there are small male cones1 but the seeds are not borne on cones1 growing instead on special short axes1 where there may be several young ovules1 but on which usually two seeds ripen4 ,the seeds are big1 and have an inner stone and outer fleshy covering4 ,some have special outer fleshy structures known as 8arils01 e4g4 the red outer cup round the yew 8berry0 7which is not a berry at all1 but a single unenclosed seed with a fleshy coat74 ,when we turn to the ,cordaite we come to a group of plants which bears distinct relationship to the preceding1 but which has a number of individual characters4 ,it is a group of which we should know nothing were it not for the fossils preserved in the ,palozoic rocks2 yet1 notwithstanding the fact that it flourished so long ago1 it is a family of which we know much4 ,at the time of the ,coal ,measures and the succeeding ,permo-carboniferous period1 it was of great importance1 and1 indeed1 in some of the ,french deposits it would seem as though whole layers of coal were composed entirely of its leaves4 ,among the fossil remains of this family there are impressions1 casts1 and true petrifactions1 so that we know both its external appearance and the internal anatomy of nearly every part of several species of the genus4 ,for a long time the various fossil remains of the plant were not recognized as belonging to each other and together forming the records of one and the same plant--the broad1 long leaves with their parallel veins were looked on as ,monocotyledons 7see fig4 #fa72 the pith casts 7see fig4 #fc7 were thought to be peculiar constricted stems1 and were called ,sternbergia2 while the wood1 which was known from its microscopic structure1 was called ,araucarioxylon--but the careful work of many masters of fossil botany1 whose laborious studies we cannot describe in detail here1 brought all these fragments together and proved them to belong to ,cordaites4 ,illustration3 ,fig4 #fa4--,leaf of ,cordaites1 l1 attached by its broad base to a ,stem1 s ,we now know that ,cordaites were large trees1 with strong upright shafts of wood1 to whose branches large simple leaves were attached4 ,the leaves were much bigger than those of any living ,gymnosperm1 even than those of the ,kauri ,pine 7a member of the ,araucariace71 and seem in some species to have exceeded #c ft4 in length4 ,the trees branched only at the top of the main shaft1 and with their huge sword-like leaves must have differed greatly in appearance from any plant now living4 ,the leaves had many parallel veins1 as can be seen in fig4 #fa1 and were attached by a broad base directly to the main stem2 thus coming closer to the ,araucarias than the other groups of ,gymnosperms in their leaf characters4 ,illustration3 ,fig4 #fb;,a4--,microscopic ,section of ,part of a ,leaf of ,cordaites ,v1 ,vascular bundle2 ,w1 wood of bundle2 sh1 its sheath2 ,s#a1 large sclerenchyma mass alternating with bundles2 ,s#b and ,s#c1 sclerenchyma caps of bundle2 ,p1 soft tissue of leaf4 ,the internal anatomy is often well preserved1 and there is a number of species of leaves whose anatomy is known4 ,as will be expected from the parallel veins1 in each section there are many vascular bundles running equidistantly through the tissue4 ,fig4 #fb;,a shows the microscopic details from a well-preserved leaf4 ,in all the species patches of sclerenchyma were developed1 and everything indicates that they were tough and well protected against loss of water1 even to a greater extent than are most of the leaves of living ,gymnosperms4 ,in the stems the pith was much larger than that in living ,gymnosperms 7where the wood is generally very solid71 and it was hollow in older stems1 except for discs of tissue across the cavity4 ,the internal cast from these stems has been described before1 and is seen in fig4 #fc4 ,illustration3 ,fig4 #fb;,b4--,much-magnified ,wood ,elements from ,cordaites ,stem seen in longitudinal section1 the type known as ,araucarioxylon4 ,note the hexagonal outlines of the bordered pits1 which lie in several rows ,the wood was formed in closely packed radiating rows by a normal cambium 7see p4 #ff71 and the trache so formed had characteristic rows of bordered pits 7see fig4 #fb;,b74 ,the wood comes nearer to that of the living ,araucarias than any other1 and indeed the numerous pieces of fossil wood of this type which are known from all the geological periods are called ,araucarioxylon4#aa ,a double strand goes out from the main mass of wood1 which afterwards divides and subdivides to provide the numerous bundles of the leaf4 ,illustration3 ,fig4 #fc4--;,cast of ,hollow ,pith of ,cordaites1 the constrictions corresponding to discs of solid tissue across the cavity ,in the case of these fossils we are fortunate enough to have the fructifications1 both male and female1 in a good state of preservation4 ,as in other ,gymnosperms1 the male and female cones are separate1 but they differed less from each other in their arrangement than do those of any of the living types hitherto mentioned4 ,they can hardly be described as true cones1 though they had something of that nature2 the seeds seem to be borne on special short stems1 round which are also sterile scales4 ,in the seed and the way it is borne perhaps the ,cordaite may be compared more nearly with the ,taxe than with the other groups4 ,a seed1 not yet ripe1 is shown in slightly diagrammatic form in fig4 #fd1 where the essential details are illustrated4 ,the seeds of this family sometimes reached a considerable size1 and had a fleshy layer which was thick in comparison with the stone1 and externally comparable with a cherry--though1 of course1 of very different nature in reality1 for ,cordaites1 like ,taxus1 is a ,gymnosperm1 with simple naked seeds1 while a cherry is the fruit of an ,angiosperm4 ,in a few words1 these are the main characters of the large group of ,cordaites1 which held the dominant position among ,gymnosperms in the ,palozoic era4 ,they have relationships1 or perhaps one should say likenesses1 to many groups4 ,their stem- and root-anatomy is similar to the ,conifer of the present day1 the position of the ovules is like that in the ,taxace1 the male cones in some measure recall those of ,ginkgo1 the anatomy of their leaves has points which are comparable with those of the ,cycads1 to which group also the large pith in the stem and the structure of some details in the seeds unite them4 ,their own specially distinctive characters lie in their crown of huge leaves1 and unbranched shaft of stem1 the similarity of their male and female inflorescences1 and some points in their pollen grains which have not been mentioned4 ,the type is a very complex one1 possibly coming near the stock which1 having branched out in various directions1 gave rise to several of the living families4 ,illustration3 ,fig4 #fd4--,representation of ,cordaites ,seed and its ,axis with ,scales1 slightly diagrammatic1 modified from ,renault4 ,a1 ,axis with s1 scales2 c1 coat of the seed1 from which the inner parts have shrunk away2 n1 nucellus2 p4c1 pollen chamber containing pollen grains which enter through m4 ,plants which come very near to the ,cordaite are the ,poroxyle4 ,of this group we have unfortunately no remains of fructifications in organic connection1 so that its actual position must remain a little doubtful till they are discovered4 ,there seems no doubt that they must have borne seeds4 ,still1 it has been abundantly demonstrated in recent years that the anatomy of the root1 stem1 and leaves indicates with considerable exactness the position of any plant1 so that1 as these are known1 we can deduce from them1 with a feeling of safety1 the position that ,poroxylon takes in the natural system4 ,in its anatomy the characters are those of the ,cordaite1 with certain details which show a more primitive nature and seem to be characteristic of the groups below it in organization4 ,poroxylon is not common1 and until recently had not been found in the ,lower ,coal ,measures of ,england4 ,the plants appear to have been much smaller than ,cordaites1 with delicate stems which bore relatively large simple leaves4 ,the anatomy of the root was that common in ,gymnosperms1 but the stem had a very large pith1 and the leaves were much like those of ,cordaites in having parallel veins4 ,an important character in the anatomy of the stem was the presence of what is known as centripetal wood4 ,this must be shortly explained4 ,in all the stems hitherto considered1 the first-formed wood cells 7protoxylems1 see p4 #eg7 developed at the central point of the wood1 towards the pith 7see fig4 #ai1 px1 p4 #di74 ,this is characteristic of all ,angiosperms and the higher ,gymnosperms 7except in a couple of recently investigated ,pines71 but among the lower plants we find that part of the later wood develops to the inner side of these protoxylem masses4 ,the distinction is shown in fig4 #fe4 ,illustration3 ,fig4 #fe4--;,a1 ,normal bundle of higher plant2 x1 protoxylem on inner side next the pith p1 and the older wood w outside it1 centrifugal wood4 ,b1 ,bundle with wood cells c developed on inner side of protoxylem1 centripetal wood2 the arrow indicates the direction of the centre of the stem4 ,this point is one to which botanists have given much attention1 and on which they have laid much weight in considering the affinities of the lower ,gymnosperms and the intermediate groups between them and the ferns1 which are found among the fossils4 ,in ,cordaites this point of connection with the lower types is not seen1 but in ,poroxylon1 which has otherwise a stem anatomy very similar to ,cordaites1 we find groups of centripetal wood developed inside the protoxylem of primary bundles4 ,for this reason1 principally1 is ,poroxylon of interest at present1 as in its stem anatomy it seems to connect the ,cordaites type with that of the group below it in general organization4 ,ginkgoales4--,reference to p4 #dd shows that ,ginkgo1 the ,maidenhair tree1 belongs to the ,ginkgoales1 a group taking equal rank with the large and complex series of the ,coniferales4 ,the ,ginkgoales of the present day1 however1 have but one living representative4 ,ginkgo stands alone1 the single living species of its genus1 representing a family so different from any other living family that it forms a prime group by itself4 ,had the tree not been held sacred in ,china and ,japan1 it is probable that it would long since have been extinct1 for it is now known only in cultivation4 ,it is indeed a relic from the past which has been fortunately preserved alive for our examination4 ,it belongs to the fossil world1 as a belated ,november rose belongs to the summer4 ,because of its beauty and interest the plant is now widely distributed under cultivation1 and is available for study almost as freely as the other types of living ,gymnosperms already mentioned1 so that but a short summary of its more important features is needed here4 ,old plants1 such as can be seen growing freely in ,japan 7in ,kew ,gardens there is also a fine specimen71 are very tall handsome woody trees1 with noble shafts and many branches4 ,the leaves grow on little side shoots and are the most characteristic external feature of the tree2 their living form is illustrated in fig4 #ff1 which shows the typical simple shape as well as the lobed form of the leaf which are to be found1 with all intermediate stages1 on the same tree4 ,no other plant 7save a few ferns1 which can generally be distinguished from it without difficulty7 has leaves at all like these1 so that it is particularly easy to identify the fossil remains1 of which there are many4 ,illustration3 ,fig4 #ff4--;,a1 ,tuft of ,ginkgo ,leaves1 showing their 8maidenhair0-like shape4 ,b1 ,single deeply-divided ,leaf to be found on the same tree1 usually on young branches4 ,the wood is compact and fine grained1 the rings of secondary tissue being developed from a normal cambium as in the case of the higher ,gymnosperms1 and the individual trache have round bordered pits4 ,there are small male cones1 but the seeds are not borne in cones4 ,they develop on special stalks on which are no scales1 but a small mass of tissue at the base of the seed called the 8collar04 ,usually there are two young ovules1 of which often only one ripens to a fleshy seed1 though both may mature4 ,illustration3 ,fig4 #fg4--,ripe ,stage of ,ginkgo ,seeds attached to their ,stalk4 c1 8,collar0 of seed4 ,the ripe seed reaches the size shown in the diagram1 and is orange coloured and very fleshy2 within it is a stone encasing the endosperm1 which is large1 green1 and starchy1 and contains the embryo with two cotyledons4 ,this embryo is small compared with the endosperm1 cf4 fig4 #eg1 p4 #gf1 which is somewhat similar to that of ,ginkgo in this stage4 ,of the microscopic characters of the reproductive organs the most remarkable is the male cell4 ,this is not a passive nucleus1 as in the plants hitherto considered1 but is an actively swimming cell of some size1 provided with a spiral of cilia 7hairlike structures7 whose movements propel it through the water4 ,in the cavity of the unripe seed these swim towards the female cell1 and actively penetrate it4 ,the arrangements of the seed are diagrammatically shown in fig4 #fh1 which should be compared with that of ,cycas1 fig4 #gf1 with which it has many points in common4 ,illustration3 ,fig4 #fh4--,section through ,seed of ,ginkgo p4c1 ,pollen chamber in the nucellus n1 which is fused to the coat c to the level l2 sc1 stony layer in coat2 ,s1 the big spore1 filled with endosperm tissue 7in this case green in colour72 e1 egg cells1 one of which will produce the embryo after fertilization4 ,the nature of the male cell in ,cordaites is not yet known1 but there is reason to suspect it may have been actively swimming also4 ,as this is uncertain1 however1 we may consider ,ginkgo the most highly organized plant which has such a primitive feature1 a feature which is a bond of union between it and the ferns1 and which1 when it was discovered about a dozen years ago1 caused a considerable sensation in the botanical world4 ,to turn now to the fossil records of this family4 ,leaf impressions of ,ginkgo are found in rocks of nearly all ages back even to the ,upper ,palozoic4 ,they show a considerable variety of form1 and it is certain that they do not all belong to the same species as the living plant1 but probably they are closely allied4 ,fig4 #fi shows a typical impression from the ,lower ,mesozoic rocks4 ,in this specimen1 the cells of the epidermis were fortunately sufficiently well preserved to be seen with the microscope1 and there is a distinct difference in the size and shape of the cells of living and fossil species1 see fig4 #gj2 but this difference is slight as compared with the great similarity of form and appearance1 as can be seen on comparing figs4 #fi and #ff1 ,b1 so that the fossil is at the most a different species of the genus ,ginkgo4 ,among the fossil leaves there is greater variety than among the living ones1 and some which are very deeply lobed so as to form a divided palm-like leaf go by different names1 e4g4 ,baiera1 but they are supposed to belong to the same family4 ,fossil seeds and male cones are also known as impressions1 and are found far back in the ,mesozoic rocks4 ,from the fossil impressions it is certain that ,ginkgo and plants closely allied to it were very widespread in the past1 as they are found all over ,europe as well as the other continents4 ,particularly in the ,lower ,mesozoic rocks ,ginkgo seems to have been a world-wide type growing in great abundance4 ,illustration3 ,fig4 #fi4--,leaf ,impression of ,ginkgo from ,mesozoic ,rocks of ,scotland ,illustration3 ,fig4 #gj4--,showing ,epidermis with ,stomates from the lower side of the ,leaf seen in fig4 #fi e1 ,epidermis cells2 s1 stomates2 v1 long cells of epidermis lying over the veins4 ,in the ,palozoic the records are not so undoubted1 but there is strong evidence which leads us to suppose that if the genus now living were not then extant1 at least other closely related genera were1 and there seems to be good grounds for supposing that ,ginkgo and ,cordaites may have both arisen from some ancient common stock4 ,,chapter ,x ,,past ,,histories ,,of ,,plant ,,families ,,iii4 ,the ,bennettitales ,this fascinating family is known only from the fossils1 and is so remote in its organization from any common living forms that it may perhaps be a little difficult for those who do not know the ,cycads to appreciate the position of ,bennettites4 ,it would probably be better for one studying fossil plants for the first time to read the chapters on the ,cycads1 ,pteridosperms1 and ,ferns before this chapter on the present group1 which has characters connecting it with that series4 ,until recently the bulk of the fossils which are found as impressions of stems and foliage of this family were very naturally classed as ,cycads4 ,they are extremely common in the ,mesozoic rocks 7the so-called ,age of ,cycads71 and in the external appearance of both stems and leaves they are practically identical with the ,cycads4 ,a few incomplete fructifications of some species have been known in ,europe for many years1 but it is only recently that they have been fully known4 ,this is owing to ,wieland's#ab work on the ,american species1 which has made known the complete organization of the fructifications from a mass of rich and well-petrified material4 ,in the ,lower ,cretaceous and ,upper ,jurassic rocks of ,america these plants abound1 with their microscopic structure well preserved1 and their fructifications show an organization of a different nature from that of any past or present ,cycad4 ,probably owing to their external appearance1 ,wieland describes the plants as 8,cycads0 in the title of his big book on them2 but the generic name he uses1 ,cycadeoidea1 seems less known in this country than the equally well-established name of ,bennettites1 which has long been used to denote the ,european specimens of this family1 and which will be used in the following short account of the group4 ,at the present time no family of fossils is exciting more interest4 ,their completely ,cycadean appearance and their unique type of fructification have led many botanists to see in them the forerunners of the ,angiosperms1 to look on them as the key to that mystery--the origin of the flowering plants4 ,this position will be discussed and the many facts in its favour noted1 but we must not forget that the ,bennettitales have only recently been realized fully by botanists1 and that a new toy is ever particularly charming1 a new cure particularly efficacious1 and a new theory all-persuasive4 ,from their detailed study of the flowering plants botanists have leaned toward different groups as the present representatives of the primitive types4 ,the various claims of the different families to this position cannot be considered here2 probably that of the ,ranales 7the group of families round ,ranunculace as a central type7 is the best supported4 ,yet these plants are most frequently delicate herbs1 which would have stood relatively less chance of fossilization than the other families which may be considered primitive4 ,they are peculiarly remote from the group of ,bennettite in their vegetative structure1 a fact the importance of which seems to have been underrated1 for in the same breath we are assured that the ,bennettites are a kind of cousin to the ancient ,angiosperms1 and that the ,ranales are among the most primitive living ,angiosperms1 and therefore presumably nearest the ancient ones4 ,however1 let us leave the charms of controversy on one side and look at the actual structure of the group4 ,they were widely spread in ,lower ,mesozoic times1 the plants being preserved as casts1 impressions1 and with structure in great numbers4 ,the bulk of the described structural specimens have been obtained from the rocks of ,england1 ,france1 ,italy1 and ,america1 although leaf impressions are almost universally known4 ,the genus ,williamsonia belongs to this family1 and is one of the best known of ,mesozoic plant impressions4 ,externally the ,bennettite were identical in appearance with stumpy ,cycads1 and their leaves it is which gave rise to the surmise1 so long prevalent1 that the ,lower ,mesozoic was the 8,age of ,cycads01 just as it was the ,pteridosperm leaves that gave the ,palozoic the credit of being the 8,age of ,ferns04 ,in the anatomy of both stem and leaf1 also1 the characters are entirely ,cycadean2 the outgoing leaf trace is indeed simpler in its course than that of the ,cycads4 ,illustration3 ,fig4 #ga4--;,half of a ,longitudinal ,section through a ,mature ,cone of ,bennettites ,a1 ,short conical axis2 s1 enclosing bracts2 ,s1 seeds2 sc1 sterile scales between the seeds4 ,the fructifications1 however1 differ fundamentally from those of the ,cycads1 as indeed they do from those of any known family4 ,they took the form of compact cones1 which occurred in very large numbers in the mature plants hidden by the leaf bases4 ,in ,williamsonia1 of which we know much less detail1 the fructifications stood away from the main axis on long pedicels4 ,in ,bennettites the cones were composed of series of sheathing scales surrounding a short conical axis on which stood thin radiating stalks1 each bearing a seed4 ,between them were long-stalked sterile scales with expanded ends4 ,a part of a cone is illustrated diagrammatically in fig4 #ga4 ,the whole had much the appearance of a complex fruit4 ,in some specimens these features alone are present in the cones1 but in younger cones from the ,american plants further structures are found attached4 ,below the main axis of the seed-bearing part of the cone was a series of large complex leaflike structures closely resembling fern leaves in their much-divided nature4 ,on the pinn of these leaves were crowded innumerable large sporangia1 similar to those of a fern1 which provided the pollen grains4 ,the fossils are particularly well preserved1 and have been found with these male 7pollen-bearing7 organs in the young unopened stages1 and also in the mature unfolded condition1 as well as the ripening seed cones from which they have faded1 just as the stamens fade from a flower when the seeds enlarge4 ,illustration3 ,fig4 #gb4--;,diagram of ,complete ,cone of ,bennettites ,a1 ,central axis of conical shape terminating in the seed-bearing cone ,s4 7,after ,wieland71 and bearing successively ,br41 bracts1 comparable with floral leaves2 ,m1 large complex leaves with pollen sacs4 ,it appears that these huge complex leaflike structures were really stamens1 but nevertheless they were rolled up in the circinate form as are young fern leaves1 and as they unrolled and spread out round the central cone they must have had the appearance of a whorl of leaves 7see fig4 #gb74 ,this1 in a few words1 is the main general character of the fructification4 ,the most important features1 on which stress is laid1 are the following4 ,the association of the male and female structures on the same axis1 with the female part above the male4 ,this arrangement is found only in the flowering plants2 the lower plants1 which have male and female on the same cone1 have them mixed1 or the female below1 and are in any case much simpler in their entire organization4 ,the conical form of the axis is also important1 as is the fact that it terminates in the seed-bearing structures4 ,illustration3 ,fig4 #gc4--;,diagram of ,cross ,section of ,bennettites1 ,seed1 with ,embryo c1 ,double-layered seed coat2 n1 crushed nucellus2 cot41 two cotyledons which practically fill the seed4 ,the position of the individual seeds1 each on the end of a single stalk1 is remarkable1 as are the long-stalked bracts whose shield-like ends join in the protection of the seeds4 ,these structures together give the cone much of the appearance of a complex fruit of a flowering plant1 but the structure of the seeds themselves is that of a simple ,gymnosperm4 ,in the seeds1 however1 was an embryo4 ,in this they differ from all known seeds of an earlier date1 which1 as has been already noted 7see p4 #gg71 are always devoid of one4 ,this embryo is one of the most important features of the plant4 ,it had two cotyledons which filled the seed space 7see fig4 #gc71 and left almost no trace of the endosperm4 ,reference to p4 #aab will show that this is an advance on the ,cycad seed1 which has a small embryo embedded in a large mass of endosperm1 and that it practically coincides with the ,dicotyledonous type4 ,the seed with its embryo suggested comparison with the ,angiosperms long before the complete structure of the fructification was known4 ,the fern-like nature of the pollen-bearing structures is another very important point4 ,were any one of these leaflike 8stamens0 found isolated its fern-like nature would not have been questioned a year or two ago1 and their presence in the 8flower0 of ,bennettites is a strong argument in favour of the ,fern-,pteridosperm affinities of the group4 ,had the parts of this remarkable fructification developed on separate trees1 or on separate branches or distinct cones of the same one1 they would have been much less suggestive than they are at present1 and the fructifications might well have been included among those of the ,gymnosperms1 differing little more 7apart from the embryo7 from the other ,gymnosperm genera than they do from each other4 ,in fact1 the extremely fern-like nature of the male organs is almost more suggestive of a ,pteridosperm affinity1 for even the simplest ,cycads have well-marked scaly cones as their male organs4 ,the female cone1 again1 considered as an isolated structure1 can be interpreted as being not vitally different from ,cordaites1 where the seeds are borne on special short stalks amidst scales4 ,the embryo would1 in any case1 point to a position among advanced types2 but it is so common for one organ of a plant to evolve along lines of its own independently1 or in advance of the other organs1 that the embryo structure alone could not have been held to counterbalance the ,cycadean stems and leaves1 the ,pteridosperm-like male organs1 and the ,gymnospermic seeds4 ,but all these parts occur on the same axis1 arranged in the manner typical of ,angiosperms4 ,the seed-bearing structures at the apex1 the 8stamens0 below them1 and a series of expanded scales below these again1 which it takes little imagination to picture as incipient petals and sepals2 and behold--the thing is a flower6 ,and being a 8flower01 is in closest connection with the ancestors of the modern flowering plants1 which must consequently have evolved from some ,cycadean-like ancestor which also gave rise to the ,bennettitales4 ,thus can the flowering plants be linked on to the series that runs through the ,cycads directly to the primitive ferns6 ,it is evident that this group1 of all those known among the fossils1 comes most closely to an approximation of ,angiospermic structure and arrangement4 ,enough has been said to show that in their actual nature they are not ,angiosperms1 though they have some of their characters1 while at the same time they are not ,cycads1 though they have their appearance4 ,they stand somewhere between the two4 ,though many botanists at present hold that this mixture of characters indicates a relationship equivalent to a kind of cousinship with the ,angiosperms1 and both groups may be supposed to have originated from a ,cycadean stock1 this theory has not yet stood the test of time1 nor is it supported by other evidence from the fossils4 ,we will go so far as to say that it appears as though some ,angiosperms arose in that way2 but flowering plants show so many points utterly differing from the whole ,cycadean stock that a little scepticism may not be unwholesome4 ,it is well to remember the ,lycopods1 where 7as we shall see1 p4 #ada7 structures very like seeds were developed at the time when the ,lycopods were the dominant plants1 and we do not find any evidence to prove that they led on to the main line of seed plants4 ,similarly1 ,cycads may have got what practically amounted to flowers at the time when they were the dominant group1 and it is very conceivable that they did not lead on to the main line of flowering plants4 ,whatever view may be held1 however1 and whatever may be the future discoveries relating to this group of plants1 we can see in the ,bennettitales points which throw much light on the potentialities of the ,cycadean stock1 and structures which have given rise to some most interesting speculations on the subject of the ,angiosperms4 ,this group is another of the jewels in the crown of fossil botany1 for the whole of its structures have been reconstructed from the stones that hold all that remains of this once extensive and now extinct family of plants4 ,,chapter ,,xi ,,past ,,histories ,,of ,,plant ,,families ,,iv4 ,the ,cycads ,the group of the ,cycadales1 which has a systematic value equivalent to the ,ginkgoales1 contains a much larger variety of genera and species than does the latter4 ,there are still living nine genera1 with more than a hundred and fifty species1 which form 7though a small one compared with most of the prime groups7 a well-defined family4 ,they are the most primitive ,gymnosperms1 the most primitive seed-bearing plants now living1 and in their appearance and characters are very different from any other modern type4 ,their external resemblance to the group of the ,bennettitales1 however1 is very striking1 and indeed1 without the fructifications it would be impossible to distinguish them4 ,the best known of the genera is that of ,cycas1 of which an illustration is given in fig4 #gd4 ,the thick1 stumpy stem and crown of 8palm0-like leaves give it a very different appearance from any other ,gymnosperm4 ,commonly the plants reach only a few feet in height1 but very old specimens may grow to the height of #cj ft4 or more4 ,the other genera are smaller1 and some have short stems and a very fern-like appearance1 as1 for example1 the genus ,stangeria1 which was supposed to be a fern when it was first discovered and before fruiting specimens had been seen4 ,the large compound leaves are all borne directly on the main stem1 generally in a single rosette at its apex1 and as they die off they leave their fleshy leaf bases1 which cover the stem and remain for an almost indefinite number of years4 ,the wood of the main trunks differs from that of the other ,gymnosperms in being very loosely built1 with a large pith and much soft tissue between the radiating bands of wood4 ,there is a cambium which adds zones of secondary tissue1 but it does not do its work regularly1 and the cross section of an old ,cycad stem shows disconnected rings of wood1 accompanied by much soft tissue4 ,the cells of the wood have bordered pits on their walls1 and in the main axis the wood is usually all developed in a centrifugal direction1 but in the axis of the cones some centripetal wood is found 7refer to c1 fig4 #fe1 p4 #ig74 ,illustration3 ,fig4 #gd4--,plant of ,cycas1 showing the main stem with the crown of leaves and the irregular branches which come on an old plant ,in their fructifications the ,cycads stand even further apart from the rest of the ,gymnosperms4 ,one striking point is the enormous size of their male cones4 ,the male cones consist of a stout axis1 round which are spiral series of closely packed simple scales covered with pollen-bearing sacs 7which bear no inconsiderable likeness to fern sporangia71 the whole cone reaching #a ft4 in length in some genera1 and weighing several pounds4 ,all the other ,gymnosperms1 except the ,araucare1 where they are an inch or two long1 have male cones but a fraction of an inch in length4 ,illustration3 ,fig4 #ge4--,seed-bearing ,scale of ,cycas1 showing its lobed and leaflike character s1 ,seeds attached on either side below the divisions of the sporophyll4 ,in all the members of the family1 excepting ,cycas itself1 the female fructifications also consist of similarly organized cones bearing a couple of seeds on each scale instead of the numerous pollen sacs4 ,in ,cycas the male cones are like those of the other genera1 and reach an enormous size2 but there are no female cones1 for the seeds are borne on special leaflike scales4 ,these are illustrated in fig4 #ge1 which shows also that there are not two seeds 7as in the other genera with cones7 to each scale1 but an indefinite number4 ,the leafy nature of the seed-bearing scale is an important and interesting feature4 ,although theoretically botanists are accustomed to accept the view that seeds are always borne on specially modified leaves 7so that to a botanist even the 8shell0 of a pea-pod and the box of a poppy capsule are leaves71 yet in ,cycas alone among living plants are seeds really found growing on a large structure which has the appearance of a leaf4 ,hence1 from this point of view 7see p4 #de1 however1 for a caution against concluding that the whole plant is similarly lowly organized71 ,cycas is the most primitive of all the living plants that bear seeds1 and hence presumably the likest to the fossil ancestors of the seed-bearing types4 ,in this character it is more primitive than the fossil group of the ,cordaite1 and comes very close to an intermediate group of fossils to be considered in the next chapter4 ,illustration3 ,fig4 #gf4--,seed of ,cycas cut open n1 ,the nucellus1 fused at the level l to the coat c2 sc1 stony layer of coat2 p4c1 pollen chamber in apex of the nucellus2 ,s1 8spore01 filled with endosperm1 in which lies the embryo e4 ,to enter into the detailed anatomy of the seeds would lead us too far into the realms of the specialist1 but we must notice one or two points about them4 ,firstly1 their very large size1 for ripe seeds of ,cycas are as large as peaches 7and peaches1 it is to be noted1 are fruits1 not seeds71 and particularly the large size they attain before they are fertilized and have an embryo4 ,among the higher plants the young seeds remain very minute until an embryo is secured by the act of fertilization1 but in the ,cycads the seeds enlarge and lay in a big store of starch in the endosperm before the embryo appears1 so that in the cases in which fertilization is prevented large1 sterile 8seeds0 are nevertheless produced4 ,this must be looked on as a want of precision in the mechanism1 and as a wasteful arrangement which is undeniably primitive4 ,an even more wasteful arrangement appears to have been common to the 8seeds0 of the ,palozoic period1 for1 though many fossil 8seeds0 are known in detail from the old rocks1 not one is known to have any trace of an embryo4 ,a general plan of the ,cycas seed is shown in fig4 #gf1 which should be compared with that of ,ginkgo 7fig4 #fh74 ,the large size of the endosperm and the thick and complex seed-coats are characteristic features of both these structures4 ,another point that makes the ,cycad seeds of special interest is the fact that the male cells 7as in ,ginkgo7 are developed as active1 free-swimming sperms1 which swim towards the female cell in the space provided for them in the seed 7see p4c1 fig4 #gf74 ,the characters of the ,cycads as they are now living prove them to be an extremely primitive group1 and therefore presumably well represented among the fossils2 and indeed among the ,mesozoic rocks there is no lack of impressions which have been described as the leaves of ,cycads4 ,there is1 however1 very little reliable material1 and practically none which shows good microscopic structure4 ,leaf impressions alone are most unsafe--more unsafe in this group1 perhaps1 than in any other--for reasons that will be apparent later on1 and the conclusions that used to be drawn about the vast number of ,cycads which inhabited the globe in the early ,mesozoic must be looked on with caution1 resulting from the experience of recent discoveries proving many of these leaves to belong to a different family4 ,there remain1 however1 many authentic specimens which show that ,cycas certainly goes back very far in history1 and specimens of this genus are known from the older ,mesozoic rocks4 ,we cannot say1 however1 as securely as used to be said1 that the ,mesozoic was the 8,age of ,cycads01 although it was doubtless the age of plants which had much of the external appearance of ,cycads4 ,from the ,palozoic we have no reliable evidence of the existence of ,cycads1 though the plants of that time included a group which has an undoubted connection with them4 ,indeed1 so far as fossil evidence goes1 we must suppose that the ,cycads1 since their appearance1 possibly at the close of the ,palozoic1 have never been a dominant or very extensive family1 though they grew in the past all over the world1 and in ,europe seem to have remained till the middle of the ,tertiary epoch4 ,,chapter ,,xii ,,past ,,histories ,,of ,,plant ,,families ,v4 ,pteridosperms ,this group consists entirely of plants which are extinct1 and which were in the height of their development in the ,coal ,measure period4 ,as a group they are the most recently discovered in the plant world1 and but a few years ago the name 8,pteridosperm0 was unknown4 ,they form1 however1 both one of the most interesting of plant families and one of the most numerous of those which flourished in the ,carboniferous period4 ,to mention first the vital point of interest in their structure1 they show leaves which in all respects appear like ordinary foliage leaves1 and yet bear seeds4 ,these leaves1 which we now know bore the seeds1 had long been considered as typical fern leaves1 and had been named and described as fern leaves4 ,there are two extremely important results from the discovery of this fossil group1 viz4 that leaves1 to all appearance like ordinary foliage1 can directly bear seeds1 and that the leaves1 though like fern leaves1 bore seeds like those of a ,cycad4 ,as the name ,pteridosperm indicates1 the group is a link between the ferns and the seed-bearing plants1 and as such is of special interest and value to botanists4 ,the gradual recognition of this group from among the numerous plant fragments of ,palozoic age is one of the most interesting of the accumulative discoveries of fossil botany4 ,ever since fossil remains attracted the attention of enquiring minds many 8ferns0 have been recognized among the rich impressions of the ,coal ,measures4 ,most of them1 however1 were not connected with any structural material1 and were given many different names of specific value4 ,so numerous were these fern 8species0 that it was supposed that in the ,coal ,measure period the ferns must have been the dominant class1 and it is often spoken of even yet as the 8,age of ,ferns04 ,from the rocks of the same age1 preserved with their microscopical structure perfect1 were stems which were called ,lyginodendron4 ,in the coal balls associated with these stems 7which were the commonest of the stems so preserved7 were also roots1 petioles1 and leaflets1 but they were isolated1 like the most of the fragments in a coal ball1 and to each was given its name1 with no thought of the various fragments having any connection with each other4 ,gradually1 however1 various fragments from the coal balls had been recognized as belonging together2 one specimen of a petiole attached to a stem sufficed to prove that all the scattered petioles of the same type belonged also to that kind of stem1 and when leaves were found attached to an isolated fragment of the petiole1 the chain of proof was complete that the leaves belonged to the stem1 and so on4 ,by a series of lengthy and painstaking investigations all the parts of the plant now called ,lyginodendron have been brought together1 and the impressions of its leaves have been connected with it1 these being of the fernlike type so long called ,sphenopteris1 illustrated in fig4 #gg4 ,illustration3 ,fig4 #gg4--,sphenopteris ,leaf ,impression1 the fernlike foliage of ,lyginodendron ,illustration3 ,fig4 #gh;,a4--,diagram of the ,transverse ,section of ,stem of the ,lyginodendron p1 ,pith2 ,p1 primary wood groups2 ,w1 secondary wood2 l4t1 leaf trace2 s1 sclerized bands in the cortex2 ,s1 longitudinal view of wood elements to show the rows of bordered pits4 ,the anatomy of the main stem is very suggestive of that of a ,cycad4 ,the zones of secondary wood are loosely built1 the quantity of soft tissue between the radiating bands of wood1 and the size of the pith being large1 while from the main axis double strands of wood run out to the leaf base4 ,the primary bundles1 however1 are not like those of a ,cycad stem1 but have groups of centripetal wood within the protoxylem1 and thus resemble the primary bundles of ,poroxylon 7see p4 #ig71 which are more primitive in this respect than those of the ,cycads4 ,the roots of ,lyginodendron1 when young1 were like those of the ,marattiaceous ferns1 their five-rayed mass of wood being characteristic of that family1 and different from the type of root found in most other ferns 7cf4 fig4 #gh;,b with fig4 #ce on p4 #fj74 ,unlike fern roots of any kind1 however1 they have well-developed zones of secondary wood1 in which they approach the ,gymnospermic roots 7see fig4 #gh;,b1 s74 ,illustration3 ,fig4 #gh;,b4--,transverse ,section of ,root of ,lyginodendron w1 ,five-rayed mass of primary wood2 s1 zone of secondary wood2 c1 cortical and other soft tissues4 ,a further mixture of characters is seen in the vascular bundles of the petioles4 ,a double strand1 like that in the lower ,gymnosperms1 goes off to the leaf base from the main axis1 but in the petiole itself the bundle is like a normal fern stele1 and shows no characters in transverse section which would separate it from the ferns4 ,such a petiole is illustrated in fig4 #gi1 with its ,v-shaped fernlike stele4 ,on the petioles and stems were certain rough1 spiny structures of the nature of complex hairs4 ,in some cases they are glandular1 as is seen in g in fig4 #gi1 and as they seem to be unique in their appearance they have been of great service in the identification of the various isolated organs of the plant4 ,as is seen from fig4 #gg1 the leaves were quite fern-like1 but in structural specimens they have been found with the characteristic glandular hairs of the plant4 ,the seeds were so long known under the name of ,lagenostoma that they are still called by it1 though they have been identified as belonging to ,lyginodendron4 ,they were small 7about in4 in maximum length7 when compared with those of most other plants of the group1 or of the ,cycads1 with which they show considerable affinity4 ,they are too complex to describe fully1 and have been mentioned already 7see p4 #gf71 so that they will not be described in much detail here4 ,the diagrammatic figure 7fig4 #ef7 shows the essential characters of their longitudinal section1 and their transverse section1 as illustrated in fig4 #hj1 shows the complex and elaborate mechanism of the apex4 ,illustration3 ,fig4 #gi4--,transverse ,section through ,petiole of ,lyginodendron v1 ,fern-like stele2 c1 cortex2 g1 glandular hairlike protuberances4 ,round the 8seed0 was a sheath1 something like the husk round a hazel nut1 which appears to have had the function of a protective organ1 though what its real morphological nature may have been is as yet an unsolved problem4 ,on the sheath were glandular hairs like those found on the petiole and leaves1 which were1 indeed1 the first clues that led to the discovery of the connection between the seed and the plant ,lyginodendron4 ,the pollen grains seem to have been produced in sacs very like fern sporangia developed on normal foliage leaves1 each grain entered the cavity pc in the seed 7see fig4 #ef71 but of the nature of the male cell we are ignorant4 ,in none of the fossils has any embryo been found in the 8seeds01 so that presumably they ripened1 or at least matured their tissues1 before fertilization4 ,these1 in a few words1 are the essentials of the structures of ,lyginodendron4 ,but this plant is only one of a group1 and at least two other of the ,pteridosperms deserve notice1 viz4 ,medullosa1 which is more complex1 and ,heterangium1 which is simpler than the central type4 ,illustration3 ,fig4 #hj4--;,diagram of ,transverse ,section of ,lagenostoma ,seed near the ,apex1 showing the nine flutings f of the coat c2 v1 the vascular strand in each2 nc1 cone of nucellar tissue standing up in the fluted apex of the nucellus n2 pc1 the pollen chamber with a few pollen grains2 s1 space between nucellus and coat4 ,compare with diagram #ef4 ,heterangium is found also in rocks rather older than the coal series of ,england1 though of ,carboniferous age1 viz4 in the ,calciferous sandstone series of ,scotland1 it occurs also in the ordinary ,coal ,measure nodules4 ,it is in several respects more primitive than ,lyginodendron1 and in particular in the structure of its stele comes nearer to that of ferns4 ,the stele is1 in fact1 a solid mass of primary wood and wood parenchyma1 corresponding in some degree to the protostele of a simple type 7see p4 #fa1 fig4 #cf71 but it has towards the outside groups of protoxylem surrounded by wood in both centripetal and centrifugal directions1 which are just like the primary bundles in ,lyginodendron4 ,outside the primary mass of wood is a zone of secondary wood1 but the quantity is not large in proportion to it 7see fig4 #ha71 as is common in ,lyginodendron4 ,though the primary mass is so fernlike in appearance the larger tracheids show series of bordered pits1 as do most of the tracheids of the ,pteridosperms1 in which they show a ,gymnosperm-like character4 ,illustration3 ,fig4 #ha4--;,heterangium ,a1 ,half of the stele of a stem1 showing the central mass of wood ,s mixed with parenchyma p4 ,the protoxylem groups p4 x4 lie towards the outside of the stele4 ,surrounding it is the narrow zone of small-celled secondary wood ,w4 ,b1 ,a few of the wood cells in longitudinal view3 p4 x41 ,protoxylem2 p1 parenchyma4 ,s1 ,large vessels with rows of bordered pits4 ,the foliage of ,heterangium was fernlike1 with much-divided leaves similar to those of ,lyginodendron4 ,we have reason to suspect1 though actual proof is wanting as yet1 that small ,gymnosperm-like seeds were borne directly on these leaves4 ,medullosa has been mentioned already 7see p4 #gb7 because of the interesting and unusually complex type of its vascular anatomy4 ,each individual stele of the group of three in the stem1 however1 is essentially similar to the stele of a ,heterangium4 ,though the whole arrangement appears to differ so widely from other stems in the plant world1 careful comparison with young stages of recent ,cycads has indicated a possible remote connection with that group1 while in the primary arrangements of the protosteles a likeness may be traced to the ferns4 ,the roots1 even in their primary tissues1 were like those of ,gymnosperms1 but the foliage with its compound leaves was quite fern-like externally4 ,a small part of a leaf is shown in fig4 #hc1 and is clearly like a fern in superficial appearance4 ,the leaves were large1 and the leaf bases strong and well supplied with very numerous branching vascular bundles4 ,illustration3 ,fig4 #hb4--,steles of ,medullosa in ,cross ,section of the ,stem ,a1 ,primary solid wood2 ,s1 surrounding secondary wood4 ,illustration3 ,fig4 #hc4--,part of a ,leaf of ,medullosa1 known as ,alethopteris1 for long supposed to be a ,fern ,the connection between this plant and certain large three-ribbed seeds known as ,trigonocarpus is strongly suspected1 though actual continuity is not yet established in any of the specimens hitherto discovered4 ,these seeds have been mentioned before 7p4 #gf and p4 #hb74 ,they were larger than the other fossil seeds which we have mentioned1 and1 with their fleshy coat1 were similar in general organization to the ,cycads1 though the fact that the seed coat stood free from the inner tissues right down to the base seems to mark them as being more primitive 7cf4 fig4 #ee1 p4 #gf74 ,of impressions of the ,pteridosperms the most striking is1 perhaps1 the foliage known as ,neuropteris 7see fig4 #f1 p4 #ac71 to which the large seeds are found actually attached 7cf4 fig4 #he74 ,illustration3 ,fig4 #hd4--;,diagrammatic ,section of a ,transverse ,section of a ,seed of ,trigonocarpus ,s1 ,stone of coat with three main ridges and six minor ones4 ,f1 ,flesh of coat3 i f1 inner flesh2 n1 nucellus1 crushed and free from coat2 s1 spore wall4 ,illustration3 ,fig4 #he4--;,fragment of ,foliage of ,neuropteris with ,seed attached1 showing the manner in which the seeds grew on the normal foliage leaves in the ,pteridosperms ,ever-increasing numbers of the 8ferns0 are being recognized as belonging to the ,pteridosperms1 but ,heterangium1 ,lyginodendron1 and ,medullosa form the three principal genera1 and are in themselves a series indicating the connection between the fernlike and ,cycadean characters4 ,before the fructifications were suspected of being seeds the anatomy of these plants was known1 and their nature was partly recognized from it alone1 though at that time they were supposed to have only fernlike spores4 ,the very numerous impressions of their fernlike foliage from the ,palozoic rocks indicate that the plants which bore such leaves must have existed at that time in great quantity4 ,they must have been1 in fact1 one of the dominant types of the vegetation of the period4 ,the recent discovery that so large a proportion of them were not ferns1 but were seed-bearing plants1 alters the long-established belief that the ferns reached their high-water mark of prosperity in the ,coal ,measure period4 ,indeed1 the fossils of this age which remain undoubtedly true ferns are far from numerous4 ,it is the seed-bearing ,pteridosperms which had their day in ,palozoic times4 ,whether they led directly on to the ,cycads is as yet uncertain1 the probability being rather that they and the ,cycads sprang from a common stock which had in some measure the tendencies of both groups4 ,that the ,pteridosperms in themselves combined many of the most important features of both ,ferns and ,gymnosperms is illustrated in the account of them given above1 which may be summarized as follows3-- ,salient ,characters of the ,pteridosperms ,g,gymnospermic ,f,fernlike ,f ,primary structure of root4 ,g ,secondary thickening of root4 ,f ,in ,heterangium and ,medullosa the ,f solid centripetal primary wood of stele4 ,g ,pits on trache of primary wood4 ,g ,secondary thickening of stem4 ,g ,double leaf trace4 ,f ,fernlike stele in petiole4 ,f ,fernlike leaves4 ,f ,sporangia pollen-sac-like4 ,f ,reproductive organs borne directly on ordinary foliage leaves4 ,g ,general organization of the seed4 ,thus it can be seen at a glance1 without entering into minuti1 that the characters are divided between the two groups with approximate equality4 ,the connection with ,ferns is clear1 and the connection with ,gymnosperms is clear4 ,the point which is not yet determined1 and about which discussion will probably long rage1 is the position of this group in the whole scheme of the plant world4 ,do they stand as a connecting link between the ferns on one hand and the whole train of higher plants on the other1 or do they lead so far as the ,cycads and there stop8 ,,chapter ,,xiii ,,past ,,histories ,,of ,,plant ,,families ,,vi4 ,the ,ferns ,unfortunately the records in the rocks do not go back so far as to touch what must have been the most interesting period in the history of the ferns1 namely1 the point where they diverged from some simple ancestral type1 or at least were sufficiently primitive to give indications of their origin from some lower group4 ,before the ,devonian period all plant impressions are of little value1 and by that early pre-,carboniferous time there are preserved complex leaves1 which are to all appearance highly organized ferns4 ,to-day the dominant family in this group is the ,polypodiace4 ,it includes nearly all our ,british ferns1 and the majority of species for the whole world4 ,this family does not appear to be very old1 however1 and it cannot be recognized with certainty beyond ,mesozoic times4 ,from the later ,mesozoic we have only material in the form of impressions1 from which it is impossible to draw accurate conclusions unless the specimens have sporangia attached to them1 and this is not often the case4 ,the cuticle of the epidermis or the spores can sometimes be studied under the microscope after special treatment1 but on the whole we have very little information about the later ,mesozoic ferns4 ,a couple of specimens from the older ,mesozoic have been recently described1 with well-preserved structure1 and they belong to the family of the ,osmundas 7the so-called 8flowering ferns01 because of the appearance of special leaves on which all the sporangia are crowded71 and show in the anatomical characters of their stems indications that they may be related to an old group1 the ,botryopteride1 in which are the most important of the ,palozoic ferns4 ,in the ,palozoic rocks there are numerous impressions as well as fern petrifactions1 but in the majority of cases the connection between the two is not yet established4 ,there were two main series of ferns1 which may be classed as belonging to ,i4 ,marattiace4 ,,ii4 ,botryopteride4 ,of these the former has still living representatives1 though the group is small and unimportant compared with what it once was2 the latter is entirely extinct1 and is chiefly developed in the ,carboniferous and succeeding ,permian periods4 ,the latter group is also the more interesting1 for its members show great variety1 and series may be made of them which seem to indicate the course taken in the advance towards the ,pteridosperm type4 ,for this reason the group will be considered first1 while the structure of the ,pteridosperms is still fresh in our minds4 ,the ,botryopteride formed an extensive and elaborate family1 with its numerous members of different degrees of complexity4 ,there is1 unfortunately1 but little known as to their external appearance1 and almost no definite information about their foliage4 ,they are principally known by the anatomy of their stems and petioles4 ,some of them had upright trunks like small tree ferns 7living tree ferns belong to quite a different family1 however71 others appear to have had underground stems1 and many were slender climbers4 ,illustration3 ,fig4 #hf4--,stele of ,asterochlaena1 showing its deeply lobed nature ,in their anatomy all the members of the family have monostelic structure 7see p4 #fb74 ,this is noteworthy1 for at the present time though a number of genera are monostelic1 no family whose members reach any considerable size or steady growth is exclusively monostelic4 ,in the shape of the single stele1 there is much variety in the different genera1 some having it so deeply lobed that only a careful examination enables one to recognize its essentially monostelic nature4 ,in fig4 #hf a radiating star-shaped type is illustrated4 ,between this elaborate type of protostele in ,asterochlaena1 and the simple solid circular mass seen in ,botryopteris itself 7fig4 #hh7 are all possible gradations of structure4 ,illustration3 ,fig4 #hg4--,the ,stele of a ,botryopteridean ,stem1 showing soft tissue in the centre of the solid wood of the protostele4 7,microphoto47 ,in several of the genera the centre of the wood is not entirely solid1 but has cells of soft tissue1 an incipient pith1 mixed with scattered tracheids1 as in fig4 #hg4 ,in most of the genera numerous petioles are given off from the main axis1 and these are often of a large size compared with it1 and may sometimes be thicker than the axis itself4 ,together with the petiole usually come off adventitious roots1 as is seen in fig4 #hh1 which shows the main axis of a ,botryopteris4 ,the petioles of the group show much variety in their structure1 and some are extremely complex4 ,a few of the shapes assumed by the steles of the petioles are seen in fig4 #hi2 they are not divided into separate bundles in any of the known forms1 as are many of the petiole steles of other families4 ,illustration3 ,fig4 #hh4--,main ,axis of ,botryopteris with simple solid ,protostele x4 ,a petiole about to detach itself p and the strand going out to an adventitious root r are also seen4 7,micro-photograph47 ,illustration3 ,fig4 #hi4--;,diagrams showing the ,shapes of the ,steles in some of the ,petioles of different ,genera of ,botryopteride ,a1 ,zygopteris2 ,b1 ,botryopteris2 ,c1 ,tubicaulis2 ,d1 ,asterochlaena4 ,in one genus of the family secondary wood has been observed4 ,this is highly suggestive of the condition of the stele in ,heterangium1 where the large mass of the primary wood is surrounded by a relatively small quantity of secondary thickening1 developed in normal radial rows from a cambium4 ,another noteworthy point in the wood of these plants is the thickening of the walls of the wood cells4 ,many of them have several rows of bordered pits1 and are1 individually1 practically indistinguishable from those of the ,pteridosperms1 cf4 fig4 #ha and fig4 #ij4 ,these are unlike the characteristic wood cells of modern ferns and of the other family of ,palozoic ferns4 ,the foliage of most members of the family is unknown1 or at least1 of the many impressions which possibly belong to the different genera1 the most part have not yet been connected with their corresponding structural material4 ,there are indications1 however1 that the leaves were large and complexly divided4 ,the fructifications were presumably fern sporangia of normal but rather massive type4 ,of most genera they are not known1 though in a few they have been found in connection with recognizable parts of their tissue4 ,the best known of the sporangia are large1 in comparison with living sporangia 7actually about #b4e millimetres long71 oval sacs clustered together on little pedicels4 ,the spores within them seem in no way essentially different from normal fern spores4 ,the coexistence of the ,botryopteride and ,pteridosperms1 and the several points in the structure of the former which seem to lead up to the characters of the latter group1 are significant4 ,the ,botryopteride1 even were they an entirely isolated group1 would be interesting from the variety of structures and the variations of the monostele in their anatomy2 and the prominent place they held in the ,palozoic flora1 as the greatest family of ferns of that period1 gives them an important position in fossil botany4 ,illustration3 ,fig4 #ij4--,trache of ,wood of ,botryopteridean ,fern in ,longitudinal ,section1 showing the rows of pits on the walls4 7,microphoto47 ,the other family of importance in ,palozoic times1 the ,marattiace1 has descendants living at the present day1 though the family is now represented by a small number of species belonging to but five genera which are confined to the tropics4 ,perhaps the best known of these is the giant 8,elephant ,fern01 which sends up from its underground stock huge complex fronds ten or a dozen feet high4 ,other species are of the more usual size and appearance of ferns1 while some have sturdy trunks above-ground supporting a crown of leaves4 ,the members of this family have a very complex anatomy1 with several series of steles of large size and irregular shape4 ,their fructifications are characteristic1 the sporangia being placed in groups of about five to a dozen1 and fused together instead of ripening as separate sacs as in the other fern families4 ,impressions of leaves with this type of sorus 7group of fern sporangia7 are found in the ,mesozoic rocks1 and these bridge over the interval between the living members of the family and those which lived in ,palozoic times4 ,in the ,coal ,measure and ,permian periods these plants flourished greatly1 and there are remains of very numerous species from that time4 ,the family was much more extensive then than it is now1 and the individual members also seem to have reached much greater dimensions1 for many of them had the habit of large tree ferns with massive trunks4 ,up till ,triassic times half of the ferns appear to have belonged to this family2 since then1 however1 they seem to have dwindled gradually down to the few genera now existing4 ,on the ,continent fossils of this type with well-preserved structure have long been known to the general public1 as their anatomy gave the stones a very beautiful appearance when polished1 so that they were used for decorative purposes by lapidaries before their scientific interest was recognized4 ,the members of the ,palozoic ,marattiace which have structure preserved generally go by the generic name ,psaronius1 in which there is a great number of species4 ,they show considerable uniformity in their essential structure 7in which they differ noticeably from the group of ferns just described71 so that but one type will be considered4 ,in external appearance they probably resembled the 8tree ferns0 of the present day 7though these belong to an entirely different family71 with massive stumps1 some of which reached a height of #fj ft4 ,the large spreading leaves were arranged in various ways on the stem1 some in a double row along it1 as is seen by the impressions of the leaf scars1 and others in complex spirals4 ,on the leaves were the spore sacs1 which were in groups1 some completely fused like those of the modern members of the family1 and others with independent sporangia massed in well-defined groups4 ,in their microscopic structure also they appear to have been closely similar to those of the living ,marattiace4 ,the transverse section of a stem shows the most characteristic and best-known view of the plant4 ,this is shown in fig4 #ia1 in somewhat diagrammatic form4 ,the mass of rootlets which entirely permeate and surround the outer tissues of the stem is a very striking and characteristic feature of all the species of ,psaronius4 ,though such a mass of roots is not found in the living species1 yet the microscopic structure of an individual fossil root is almost identical with that of a living ,marattia4 ,though these plants were so successful and so important in ,palozoic times1 the group even then seems to have possessed little variety and little potentiality for advance in new directions4 ,they stand apart from the other fossils1 and the few forms which now compose the living ,marattiace are isolated from the present successful types of modern ferns4 ,from the ,psaronie we can trace no development towards a modern series of plants1 no connection with another important group in the past4 ,they appear to have culminated in the later ,palozoic and to have slowly dwindled ever since4 ,it has been suggested that the male fructifications of the ,bennettite and the ,pteridosperms show some likeness to the ,marattiace1 but there does not seem much to support any view of phylogenetic connection between them4 ,illustration3 ,fig4 #ia4--,transverse ,section of ,stem of ,psaronius v1 ,numerous irregularly-shaped steles2 s1 irregular patches of sclerenchyma2 l1 leaf trace going out as a horseshoe-shaped stele2 c1 zone of cortex with numerous adventitious roots r running through it2 sc1 sclerized cortical zone of roots2 w1 vascular strand of roots4 ,before leaving the palozoic ferns1 mention should be made of the very numerous leaf impressions which seem to show true fern characters1 though they have not been connected with material showing their internal structure4 ,among them it is rare to get impressions with the sori or sporangia1 but such are known and are in themselves enough to prove the contention that true ferns existed in the ,palozoic epoch4 ,for it might be mentioned as a scientific curiosity1 that after the discovery that so many of the leaf impressions which had always been supposed to be ferns1 really belonged to the seed-bearing ,pteridosperms1 there was a period of panic among some botanists1 who brought forward the startling idea that there were no ferns at all in the ,palozoic periods1 and that modern ferns were degenerated seed-bearing plants6 ,illustration3 ,fig4 #ib4--;,impression of ,palozoic ,fern1 showing sori on the pinnules4 7,photo47 ,these two big groups from the ,palozoic include practically all the ferns that then flourished4 ,they have been spoken of 7together with a few other types of which little is known7 as the ,primofilices1 a name which emphasizes their primitive characters4 ,as can be seen by the complex organization of the genera1 however1 they themselves had advanced far beyond their really primitive ancestors4 ,there is clear indication that the ,botryopteride were in a period of change1 what might almost be termed a condition of flux1 and that from their central types various families separated and specialized4 ,behind the ,botryopteride1 however1 we have no specimens to show us the connection between them and the simpler groups from which they must have sprung4 ,from a detailed comparative study of plant anatomy we can deduce some of the essential characters of such ancestral plants1 but here the realm of fossil botany ceases1 to give place to theoretical speculation4 ,as a fact1 there is a deep abyss between the ferns and the other families of the ,pteridophytes1 which is not yet bridged firmly enough for any but specialists1 used to the hazardous footing on such structures1 to attempt to cross it4 ,until the buttresses and pillars of the bridge are built of the strong stone of fossil structures we must beware of setting out on what would prove a perilous journey4 ,in the ,coal ,measures and previous periods we see the ferns already represented by two large families1 differing greatly from each other1 and from the main families of modern ferns which sprung at a later date from some stock which we have not yet recognized4 ,but though their past is so obscure1 the palozoic ferns and their allies throw a brilliant light on the course of evolution of the higher groups of plants1 and the gulf between ferns and seed-bearing types may be said to be securely bridged by the ,botryopteride and the ,pteridosperms4 ,,chapter ,,xiv ,,past ,,histories ,,of ,,plant ,,families ,,vii4 ,the ,lycopods ,the present-day members of this family are not at all impressive1 and in their lowliness may well be overlooked by one who is not interested in unpretending plants4 ,the fresh green mosslike ,selaginella grown by florists as ornamental borders in greenhouses and the creeping 8club moss0 twining among the heather on a ,highland moor are probably the best known of the living representatives of the ,lycopods4 ,in the past the group held a very different position1 and in the distant era of the ,coal ,measures it held a dominant one4 ,many of the giants of the forest belonged to the family 7see frontispiece71 and the number of species it contained was very great4 ,let us turn at once to this halcyon period of the group4 ,the history of the times intervening between it and the present is but the tale of the dying out of the large species1 and the gradual shrinking of the family and dwarfing of its representative genera4 ,it is difficult to give the characters of a scientific family in a few simple words2 but perhaps we may describe the living ,lycopods as plants with creeping stems which divide and subdivide into two with great regularity1 and which bear large numbers of very small pointed leaves closely arranged round the stem4 ,the fruiting organs come at the tips of the branches1 and sometimes themselves divide into two1 and in these cone-like axes the spore cases are arranged1 a single one on the upper side of each of the scales 7see p4 #fg1 fig4 #df1 ,a74 ,in the ,lycopods the spores are all alike1 in the ,selaginellas there are larger spores borne in a small number 7four7 in some sporangia 7see fig4 #ec1 p4 #ge71 and others in large numbers and of smaller size on the scales above them4 ,the stems are all very slender1 and have no zones of secondary wood4 ,they generally creep or climb1 and from them are put out long structures something like roots in appearance1 which are specially modified stem-like organs giving rise to roots4 ,from the fossils of the ,coal ,measures ,lepidodendron must be chosen as the example for comparison4 ,the different species of this genus are very numerous1 and the various fossilized remains of it are among the commonest and best known of palontological specimens4 ,the huge stems are objects of public interest1 and have been preserved in the ,victoria ,park in ,glasgow in their original position in the rocks1 apparently as they grew with their spreading rootlike organs running horizontally4 ,a great stump is also preserved in the ,manchester ,museum1 and is figured in the frontispiece4 ,while among the casts and impressions the leaf bases of the plant are among the best preserved and the most beautiful 7see fig4 #ic74 ,the cone has already been illustrated 7see fig4 #df and fig4 #i71 and is one of the best known of fossil fructifications4 ,illustration3 ,fig4 #ic4--,photo of ,leaf ,bases of ,lepidodendron ,c1 ,scar of leaf2 ,s1 leaf base4 ,in the scar3 v1 mark of severed vascular bundle1 and p1 of parichnos4 l1 ,ligule scar4 ,from the abundant1 though scattered material1 fossil botanists have reconstructed the plants in all their detail4 ,the trunks were lofty and of great thickness1 bearing towards the apex a much-branched crown1 the branches1 even down to the finest twigs1 all dividing into two equal parts4 ,the leaves1 as would be expected from the great size of the plants1 were much bigger than those of the recent species 7fig4 #ic shows the actual size of the leaf bases71 but they were of the same relatively small size as compared with the stems1 and of the same simple pointed shape4 ,a transverse section across the apex of a fertile branch shows these closely packed leaves arranged in series round the axis1 those towards the outside show the central vascular strand which runs through each4 ,illustration3 ,fig4 #id4--,section across an ,axis surrounded by many ,leaves1 which shows their simple shape and single central vascular bundle v ,the markings left on the well-preserved leaf-scars indicate the main features of the internal anatomy of the leaves4 ,they had a single central vascular strand 7v1 fig4 #ic71 on either side of which ran a strand of soft tissue p called the parichnos1 which is characteristic of the plants of this group4 ,while another similarly obscure structure associated with the leaf is the little scale-like ligule l on its upper surface4 ,the anatomy of the stems is interesting1 for in the different species different stages of advance are to be found1 from the simple solid protostele with a uniform mass of wood to hollow ring steles with a pith4 ,an interesting intermediate stage between these two is found in ,lepidodendron selaginoides 7see fig4 #ie71 where the central cells of the wood are not true water-conducting cells1 but short irregular water-storage tracheides 7see p4 #ef71 which are mixed with parenchyma4 ,all the genera of these fossils have a single central stele1 round which it is usual to find a zone of secondary wood of greater or less extent according to the age of the plant4 ,illustration3 ,fig4 #ie4--,transverse ,section of ,lepidodendron selaginoides1 showing the circular mass of primary wood1 the central cells of which are irregular water-storage tracheides s1 ,zone of secondary wood2 c1 inner cortical tissues2 r1 intrusive burrowing rootlet2 oc1 outer cortical tissues with corky external layers k4 7,microphoto47 ,some stems instead of this compact central stele have a ring of wood with an extensive pith4 ,such a type is illustrated in fig4 #if1 which shows but a part of the circle of wood1 and the zone of the secondary wood outside it1 which greatly exceeds the primary mass in thickness4 ,this zone of secondary wood became very extensive in old stems1 for1 as will be imagined1 the primary wood was not sufficient to supply the large trunks4 ,the method of its development from a normal cambium in radiating rows of uniform tracheides is quite similar to that which is found in the pines to-day4 ,this is the most important difference between the living and the fossil stems of the family1 for no living plants of the family have such secondary wood4 ,on the other hand1 the individual elements of this wood are different from those of the higher families hitherto considered1 and have narrow slit-like pits separated by bands of thickening on the longitudinal walls4 ,such tracheides are found commonly in the ,pteridophytes1 both living and fossil4 ,their type is seen in fig4 #if1 ,b1 which should be compared with that in figs4 #gh1 ,a and #fb1 ,b to see the contrast with the higher groups4 ,illustration3 ,fig4 #if4--;,a1 ,lepidodendron ,stem with ,hollow ,ring of ,wood ,w and ,zone of ,secondary ,wood ,s4 ,b1 ,longitudinal ,view of the ,narrow ,pits of the ,wood ,elements4 ,to supply the vascular tissues of the leaf traces1 simple strands come off from the outer part of the primary wood1 where groups of small-celled protoxylem project 7see px in fig4 #ig74 ,the leaf strands lt move out through the cortex in considerable numbers to supply the many leaves1 into each of which a single one enters4 ,illustration3 ,fig4 #ig4--,transverse ,section of ,outer ,part of ,primary ,wood of ,lepidodendron1 showing px1 projecting protoxylem groups2 lt1 leaf trace coming from the stele and passing 7as lt#a7 through the cortex ,as regards the fructifications of ,lepidodendron much could be said were there space4 ,the many genera of ,lepidodendron bore several distinct types of cones of different degrees of complexity4 ,in several of the genera the cones were simple in organization1 directly comparable with those of the living ,lycopods1 though on a much larger scale 7see p4 #fg74 ,in some the spores were uniform1 all developing equally in numerous tetrads4 ,the sporophyll was radially extended1 and along it the large sausage-shaped sporangia were attached 7see fig4 #ih74 ,the tips of the sporophylls overlapped and afforded protection to the sporangia4 ,the axis of the cone had a central stele with wood elements like those in the stem4 ,the appearance of a transverse section of an actual cone is shown in fig4 #ii4 ,here the sporangia are irregular in shape1 owing to their contraction after ripeness and during fossilization4 ,other cones had sporangia similar in size and shape1 but which produced spores of two kinds1 large ones resulting from the ripening of only two or three tetrads in the lower sporangia1 and numerous small ones in the sporangia above4 ,illustration3 ,fig4 #ih4--,longitudinal ,diagram1 showing the arrangement of the elongated sporangia on the sporophylls a1 ,main axis1 round which the sporophylls are inserted2 ,s1 sporangium2 s1 leaflike end of sporophyll4 ,the similarity between the ,lepidodendron and the modern ,lycopod cone has been pointed out already 7p4 #fg71 and it is this which forms the principal guarantee that they belong to the same family1 though the size and wood development of the palozoic and the modern plants differ so greatly4 ,the large group of the ,lepidodendra included some members whose fructifications had advanced so far beyond the simple sporangial cones described above as to approach very closely to seeds in their construction4 ,this type was described on p4 #ge1 fig4 #ed1 in a series of female fructifications1 so that its essential structure need not be recapitulated4 ,illustration3 ,fig4 #ii4--,transverse ,section through ,cone of ,lepidodendron ,a1 ,main axis with woody tissue2 st1 stalks of sporophylls cut in oblique longitudinal direction2 s1 tips of sporophylls cut across2 ,s1 sporangia with a few groups of spores4 7,microphoto47 ,the section shown in fig4 #ajj is that cut at right angles to that in which the sporangia are shown in fig4 #ih1 viz4 tangential to the axis4 ,a remarkable feature of the plant is that there were also round those sporangia which bore the numerous small spores 7corresponding to pollen grains7 enclosing integument-like flaps similar to those shown in fig4 #ajj1 sp4 f4 ,illustration3 ,fig4 #ajj4--,section through one ,sporangium of ,lepidocarpon sp1 ,sporophyll2 sp4f41 flaps of sporophyll protecting sporangium2 ,s1 large spore within the sporangium wall w2 s1 the three aborted spores of the tetrad to which ,s belongs4 ,this type of fructification is the nearest approach to seed and pollen grains reached by any of the ,pteridophytes1 and its appearance at a time when the ,lycopods were one of the dominant families is suggestive of the effect that such a position has on the families occupying it1 however lowly they may be4 ,the simple ,pteridophyte ,lycopods had not only the tall trunks and solid woody structure of a modern tree1 but also a semblance of its seeds4 ,whether this line of development ever led on to any of the higher families is still uncertain4 ,the feeling of most specialists is that it did not2 but there are not wanting men who support the view that the lycopod affinity evolved in time and entered the ranks of the higher plants1 and indeed there are many points of superficial likeness between the palozoic ,lycopods and the ,conifer4 ,judged from their internal structure1 however1 the series through the ferns and ,pteridosperms leads much more convincingly to the seed plants4 ,in their roots1 or rather in the underground structures commonly called roots1 the ,lepidodendrons were also remarkable4 ,even more symmetrically than in their above-ground branching1 the base of their trunks divided2 there were four main large divisions1 each of which branched into two and these into two again4 ,these structures were called ,stigmaria1 and were common to all species of ,lepidodendron and also the group of ,sigillaria 7see fig4 #ajb74 ,on these horizontally running structures 7well shown in the frontispiece7 small appendages were borne all over their surface in great profusion1 which were1 both in their function and microscopic structure1 rootlets4 ,they left circular scars of a characteristic appearance on the big trunks1 of which they were the only appendages4 ,these scars show clearly on the fragments along the ledge to the left of the photograph4 ,the exact morphological nature of the big axes is not known2 their anatomy is not like that of roots1 but is that of a stem1 yet they do not bear what practically every stem1 whether underground or not1 has developed1 namely leaves1 or scales representing reduced leaves4 ,their nature has been commented on previously 7p4 #fi71 and we cannot discuss the point further1 but must be content to consider them as a form of root-bearing stem1 practically confined to the ,lycopods and principally developed among the palozoic fossils of that group4 ,illustration3 ,fig4 #aja4--,transverse ,section through a ,rootlet of ,stigmaria oc1 ,outer cortex2 s1 space2 ic1 inner cortex2 w1 wood of vascular strand 7wood only preserved72 px1 protoxylem group4 ,in microscopic structure the rootlets are extremely well known1 because in their growth they have penetrated the masses of the tissues of other plants which were being petrified and have become petrified with them4 ,the mass of decaying vegetable tissue on which the living plants of the period flourished were everywhere pierced by these intrusive rootlets1 and they are found petrified inside otherwise perfect seeds1 in the hearts of woody stems1 in leaves and sporangia1 and sometimes even inside each other6 ,fig4 #ie shows such a root r lying in the space left by the decay of the soft tissue of the inner cortex in an otherwise excellently preserved ,lepidodendron stem 7see also fig4 #aja74 ,in fig4 #aja their simple structure is seen4 ,they are often extremely irregular in shape1 owing to the way they seem to have twisted and flattened themselves in order to fit into the tissues they were penetrating4 ,no root hairs seem to have been developed in these rootlets1 but otherwise their structure is that of a typical simple root1 and very like the swamp-penetrating rootlets of the living ,isoetes4 ,the ,stigmarian axes and their rootlets are very commonly found in the 8underclays0 and 8gannister0 beds which lie below the coal seams 7see p4 #be71 and they may sometimes be seen attached to a bit of the trunk growing upwards through the layers4 ,they and the aerial stems of ,lepidodendron are perhaps the commonest and most widely known of fossil plants4 ,before leaving the palozoic ,lycopods another genus must be mentioned1 which is also a widely spread and important one1 though it is less well known than its contemporary4 ,the genus ,sigillaria is best known by its impressions and casts of stems covered by leaf scars4 ,the stems were sometimes deeply ribbed1 and the leaf scars were arranged in rows and were more or less hexagonal in outline1 as is seen in fig4 #ajb1 which shows a cast and its reverse of the stem of a typical ,sigillaria4 ,illustration3 ,fig4 #ajb4--;,cast and ,reverse of ,leaf ,scars of ,sigillaria4 ,in ,a the shape of the leaf bases is clearly shown1 the central markings in each being the scar of the vascular bundle and parichnos ,in its primary wood ,sigillaria differed from ,lepidodendron in being more remote from the type with a primary solid stele4 ,its woody structure was that of a ring1 in some cases irregularly broken up into crescent-shaped bundles4 ,the secondary wood was quite similar to that of ,lepidodendron4 ,stigmaria and its rootlets belong equally to the two plants1 and hitherto it has been impossible to tell whether any given specimen of ,stigmaria had belonged to a ,lepidodendron or a ,sigillaria4 ,between the two genera there certainly existed the closest affinity and similarity in general appearance4 ,these two genera represent the climax of development of the ,lycopod family4 ,in the ,lower ,mesozoic some large forms are still found1 but all through the ,mesozoic periods the group dwindled1 and in the ,tertiary little is known of it1 and it seems to have taken the retiring position it occupies to-day4 ,,chapter ,,xv ,,past ,,histories ,,of ,,plant ,,families ,,viii4 ,the ,horsetails ,the horsetails of to-day all belong to the one genus1 ,equisetum1 among the different species of which there is a remarkably close similarity4 ,most of the species love swampy land1 and even grow standing up through water2 but some live on the dry clay of ploughed fields4 ,wherever they grow they usually congregate in large numbers1 and form little groves together4 ,they are easily recognized by their delicate stems1 branching in bottle-brush fashion1 and the small leaves arranged round them in whorls1 with their narrow teeth joined to a ring at the base4 ,at the end of some of the branches come the cones1 with compactly arranged and simple sporophylls all of one kind4 ,in ,england most plants of this family are but a few inches or a foot in height1 though one species sometimes reaches #f ft41 while in ,south ,america there are groves of delicate-stemmed plants #bj ft4 high4 ,the ribbed stems and the whorls of small1 finely toothed leaves are the most important external characteristics of the plants1 while in their internal anatomy the hollow stems have very little wood1 which is arranged in a series of small bundles1 each associated with a hollow canal in the ground tissue4 ,the family stands apart from all others1 and even between it and the group of ,lycopods there seems to be a big gap across which stretch no bonds of affinity4 ,has the group always been in a similar position1 and stood isolated in a backwater of the stream of plant life8 ,illustration3 ,fig4 #ajc4--;,impression of ,leaf ,whorl of ,equisetites from the ,mesozoic ,rocks1 showing the narrow toothed form of the leaves4 7,photo47 ,in the late ,tertiary period they seem to have held much the same position as they do now1 and we learn nothing new of them from rocks of that age4 ,when1 however1 we come to the ,mesozoic1 the members of the family are of greater size1 though they appear 7to judge from their external appearance7 to have been practically identical with those now living in all their arrangements4 ,in some beds their impressions are very numerous1 but unfortunately most are without any indication of internal structure4 ,fossils from the ,mesozoic are called ,equisetites1 a name which indicates that they come very close to the living ones in their characters4 ,in the ,lower ,mesozoic some of these stems seem to have reached the great size of a couple of feet in circumference1 but to have no essential difference from the others of the group4 ,when1 however1 we come to the ,palozoic rocks we find many specimens with their structure preserved1 and we are at once in a very different position as regards the family4 ,first in the ,permian we meet with the important genus of plant called ,calamites1 which were very abundant in the ,coal ,measures4 ,many of the ,calamites were of great size1 for specimens with large trunks have been found #cj ft4 and more long1 which when growing must certainly have been much taller than that4 ,the number of individuals must also have been very great1 for casts and impressions of the genus are among the commonest fossils4 ,they were1 in fact1 one of the dominant groups of the period4 ,like the ,lycopods1 the ,equisetace reached their high-water mark of development in the ,carboniferous period2 at that time the plants were most numerous1 and of the largest size and most complicated structure that they ever attained4 ,illustration3 ,fig4 #ajd4--,small ,branches attached to stouter ,axis of ,calamites4 ,photo of ,impression ,as will be immediately suspected from analogy with the ,lycopods1 they differed from the modern members of the family in their strongly developed anatomy1 and in the strength and quantity of their secondary wood4 ,yet in their external appearance they probably resembled the living genus in all essentials1 and the groves of the larger ones of to-day growing in the marshes probably have the appearance that the palozoic plants would have had if looked at through a reversed opera glass4 ,fig4 #ajd is a photograph of some of the small branches of a ,calamite1 in which the ribbed stem can be seen1 and on the small side twigs the fine1 pointed leaves lying in whorls4 ,in most of the fossil specimens1 however1 particularly the larger ones1 the ribs are not those of the true surface1 but are those marked on the internal cast of the pith4 ,illustration3 ,fig4 #aje4--,transverse ,section of ,calamites ,stem with ,secondary ,wood w formed in ,regular ,radial ,rows in a ,solid ,ring c1 ,canals associated with the primary bundles2 p1 cells of the pith1 which is hollow with a cavity l1 cor1 ,cortex and outer tissues well preserved4 7,microphoto47 ,among tissue petrifactions there are many ,calamite stems of various stages of growth4 ,in the very young ones there are only primary bundles1 and these little stems are like those of a living ,equisetum in their anatomy1 and have a hollow pith and small vascular bundles with canals associated4 ,the fossil forms1 however1 soon began to grow secondary wood1 which developed in regular radial rows from a cambium behind the primary bundles and joined to a complete ring4 ,a stem in this stage of development is seen in fig4 #aje1 where only the wood and internal tissues are preserved4 ,the very characteristic canals associated with the primary bundles are clearly shown4 ,the amount of secondary wood steadily increased as the stems grew 7there appear to have been no 8annual rings07 till there was a very large quantity of secondary tissue of regular texture1 through which ran small medullary rays1 so that the stems became increasingly like those of the higher plants as they grew older4 ,it is the primary structure which is the important factor in considering their affinity1 and that is essentially the same as in the other members of the family in which secondary thickening is not developed4 ,as we have seen already in other groups of fossils1 secondary wood appears to develop on similar lines whenever it is needed in any group1 and therefore has but little value as an indication of systematic position4 ,this important fact is one1 however1 which has only been realized as a result of the study of fossil plants4 ,illustration3 ,fig4 #ajf4--;,diagram of the ,arrangement of the ,bundles at the ,node of a ,calamite1 showing how those of consecutive internodes alternate n1 ,region of node ,illustration3 ,fig4 #ajg4--,leaf of ,calamites in ,cross ,section v1 ,vascular bundles2 s1 cells of sheath1 filled with blackened contents2 p1 palisade cells2 e1 epidermis4 ,the longitudinal section of the stems1 when cut tangentially1 is very characteristic1 as the bundles run straight down to each node and there divide1 the neighbouring halves joining so that the bundles of each node alternate with those of the ones above and below it 7see fig4 #ajf74 ,the leaves which were attached at the nodes were naturally much larger than those of the present ,equisetums1 though they were similarly simple and undivided4 ,their anatomy is preserved in a number of cases 7see fig4 #ajg71 and was simple1 with a single small strand of vascular tissue lying in the centre4 ,they had certain large cells1 sometimes very black in the fossils1 which may have been filled with mucilage4 ,illustration3 ,fig4 #ajh4--,transverse ,section of ,young ,root of ,calamites w1 ,wood of axis2 l1 spaces in the lacunar cortex1 whose radiating strands r are somewhat crushed2 ex1 outermost cells of cortex with thickened wall4 ,illustration3 ,fig4 #aji4--;,diagram of ,cone of ,calamites ,a1 ,main axis2 br1 sterile bracts2 sp1 sporophylls with four sporangia ,s attached to each1 of which two only are seen4 ,the young roots of these plants have a very characteristic cortex1 which consists of cells loosely built together in a lacelike fashion1 with large air spaces1 so that they are much like water plants in their appearance 7see fig4 #ajh74 ,indeed1 so unlike the old roots and the stems are they1 that for long they were called by another name and supposed to be submerged stems1 but their connection with ,calamites is now quite certain4 ,as their woody axis develops1 the secondary tissue increases and pushes off the lacelike cortex1 and the roots become very similar in their anatomy to the stems4 ,both have similar zones of secondary wood1 but the roots do not have those primary canals which are so characteristic of the stems1 and thereby they can be readily distinguished from them4 ,the fructifications of the ,calamites were not unlike those of the living types of the family1 though in some respects slightly more complex4 ,round each cone axis developed rings of sporophylls which alternated with sterile sheathing bracts4 ,each sporophyll was shaped like a small umbrella with four spokes1 and stood at right angles to the axis1 bearing a sporangium at each of the spokes4 ,a diagram of this arrangement is seen in fig4 #aji4 ,illustration3 ,fig4 #aaj4--,longitudinal ,section of ,part of ,calamites ,cone br1 ,sterile bracts attached to axis2 sp1 attachment of sporophylls2 ,s1 sporangia4 ,at ,x a group of four sporangia is seen round the sporophyll1 which is seen at a4 7,microphoto47 ,a photograph of an actual section of such a cone1 cut slightly obliquely through the length of the axis1 is seen in fig4 #aaj1 where the upper groups of sporangia are cut tangentially1 and show their grouping round the sporophyll to which they are attached4 ,a few single tetrads of spores are enlarged in fig4 #aaa1 where it will be seen that the large spores are of a similar size1 but that the small ones of the tetrads are very irregular4 ,they are aborting members of the tetrad1 and appear to have been used as food by the other spores4 ,in each sporangium large numbers of these tetrads develop and all the ripe spores seem to have been of one size4 ,in a species of ,calamites 7,c4 casheana71 otherwise very similar to the common one we have been considering1 there is a distinct difference in the sizes of the spores from different sporangia4 ,the small ones1 however1 were only about one-third of the diameter of the large ones1 so that the difference was very much less marked than it was between the small and large spores of the ,lycopods4 ,among the palozoic members of the group are other genera closely allied to1 but differing from ,calamites in some particulars4 ,one of these is ,archocalamites1 which has a cone almost identical with that of the living ,equisetums1 as it has no sterile bracts mingled with the umbrella-like sporophylls4 ,other genera are more complex than those described for ,calamites1 and even in the simple coned ,archocalamites itself the leaves are finely branched and divided instead of being simple scales4 ,but no genus is so completely known as is ,calamites1 which will itself suffice as an illustration of the palozoic ,equisetace4 ,though the genus1 as was pointed out above1 shows several important characters differing from those of ,equisetum1 and parallel to some extent to those of the palozoic ,lycopods1 yet these features are more of a physiological nature than a systematic one1 and they throw no light on the origin of the family or on its connection with the other ,pteridophytes4 ,it is in the extinct family dealt with in the next chapter that we find what some consider as a clue to the solution of these problems4 ,illustration3 ,fig4 #aaa4--,tetrads of ,spores of ,calamites ,s1 ,normal-sized spores2 a1 b1 c41 aborting spores4 ,,chapter ,,xvi ,,past ,,histories ,,of ,,plant ,,families ,,ix4 ,sphenophyllales ,the group to which ,sphenophyllum belongs is of considerable interest and importance1 and is1 further1 one of those extinct families whose very existence would never have been suspected had it not been discovered by fossil botanists4 ,not only is the family as a whole extinct1 it also shows features in its anatomy which are not to be paralleled among living stems4 ,sphenophyllum became extinct in the ,palozoic period1 but its interest is very real and living to-day1 and in the peculiar features of its structure we see the first clue that suggests a common ancestor for the still living groups of ,lycopods and ,equisetace1 which now stand so isolated and far apart4 ,before1 however1 we can consider the affinities of the group1 we must describe the structure of a typical plant belonging to it4 ,the genus ,sphenophyllum includes several species 7for which there are no common ,english names1 as they are only known to science7 whose differences are of less importance than their points of similarity1 so that one species only1 ,s4 plurifoliatum1 will be described4 ,we have a general knowledge of the external appearance of ,sphenophyllum from the numerous impressions of leaves attached to twigs which are found in the rocks of the ,carboniferous period4 ,these impressions present a good deal of variety1 but all have rather delicate stems with whorls of leaves attached at regular intervals4 ,the specimens are generally easy to recognize from the shape of the leaves1 which are like broad wedges attached at the point 7see fig4 #aab74 ,in some cases the leaves are more finely divided and less fanlike1 and it may even happen that on the same branch some may be wedge-shaped like those in fig4 #aab1 and others almost hairlike4 ,this naturally suggests comparison with water plants1 which have finely divided submerged leaves and expanded aerial ones4 ,in the case of ,sphenophyllum1 however1 the divided leaves sometimes come at the upper ends of the stems1 quite near the cones1 and so can hardly have been those of a submerged part4 ,the very delicate stems and some points in their internal anatomy suggest that the plant was a trailing creeper which supported itself on the stouter stems of other plants4 ,illustration3 ,fig4 #aab4--;,impression of ,sphenophyllum ,leaves attached to the ,stem1 showing the wedge-shaped leaflets arranged in whorls ,the stems were ribbed1 but unlike those of the ,calamites the ribs ran straight down the stem through the nodes1 and did not alternate there1 so that the bundles at the node did not branch and fuse as they did in ,calamites4 ,the external appearance of the long slender cones was not unlike that of the ,calamite cones1 though their internal details showed important distinctions4 ,in one noticeable external feature the plants differed from those of the last two groups considered1 and that was in their size4 ,palozoic ,lycopods and ,equisetace reached the dimensions of great trees1 but hitherto no treelike form of ,sphenophyllum has been discovered1 and in the structure-petrifactions the largest stems we know were less than an inch in diameter4 ,in the internal anatomy of these stems lies one of the chief interests and peculiarities of the plants4 ,in the very young stage there was a sharply pointed solid triangle of wood in the centre 7fig4 #aac71 at each of the corners of which was a group of small cells1 the protoxylems4 ,the structure of such a stem is like that of a root1 in which the primary wood all grows inwards from the protoxylems towards the centre1 and had we had nothing but these isolated young stems it would have been impossible to recognize their true nature4 ,illustration3 ,fig4 #aac4--,sphenophyllum1 ,transverse ,section of ,young ,stem c1 ,cortex1 the soft tissue within which has decayed and left a space1 in which lies the solid triangle of wood1 with the small protoxylem groups px at each corner4 7,microphoto47 ,such very young stems are rare1 for the development of secondary wood began early1 and it soon greatly exceeded the primary wood in amount4 ,fig4 #aad shows a photograph of a stem in which the secondary wood is well developed4 ,the primary triangle of wood is still to be seen in the centre1 and corresponds to that in fig4 #aac1 while closely fitting to it are the bays of the first-formed secondary wood1 which makes the wood mass roughly circular4 ,outside this the secondary wood forms a regular cylinder round the axis1 which shows no sign of annual rings4 ,the cells of the wood are large and approximately square in shape1 while at the angles formed at the junction of every four cells is a group of small1 thin-walled parenchyma1 see fig4 #aae4 ,there are no medullary rays going out radially through the wood1 such as are found in all other zones of secondary wood1 and in this arrangement of soft tissue the plants are unique4 ,illustration3 ,fig4 #aad4--,sphenophyllum1 ,transverse ,section with ,secondary ,wood ,w4 ,at c the cork formation is to be seen4 7,microphoto47 ,beyond the wood was a zone of soft tissue and phloem1 which is not often preserved1 while outside that was the cork1 which added to the cortical tissues as the stem grew 7see fig4 #aad1 c74 ,illustration3 ,fig4 #aae4--;,group of ,wood ,cells w1 showing their shape and the small soft-walled cells at the angles between them p ,petrified material of leaves and roots is rare1 and both are chiefly known through the work of the ,french palobotanist ,renault4 ,the leaves are chiefly remarkable for the bands of sclerized strengthening tissue1 and generally had the structure of aerial1 not submerged leaves4 ,the roots were simple in structure1 and1 as in ,calamites1 had secondary tissue like that in the stems4 ,in the case of the fructifications it is the ,english material which has yielded the most illuminating specimens4 ,the cones were long and slender1 externally covered by the closely packed tips of the scales1 which overlapped deeply4 ,between the whorls of scales lay the sporangia1 attached to their upper sides by slender stalks4 ,a diagram will best explain how they were arranged 7see fig4 #aaf74 ,two sporangia were attached to each bract1 but their stalks were of different lengths1 so that one sporangium lay near the axis and one lay outside it toward the tip of the bract4 ,illustration3 ,fig4 #aaf4--;,diagram of ,arrangement of ,scales and ,sporangia in ,cones of ,sphenophyllum ,a1 ,axis2 br1 bract2 ,s1 sporangium1 with stalk st4 ,in its anatomy the stalk of the cone has certain features similar to those in the stem proper1 which were among the first indications that led to the discovery that the cone belonged to ,sphenophyllum4 ,there were numerous spores in each of the sporangia1 which had coats ornamented with little spines when they were ripe 7fig4 #aag1 if examined with a magnifying glass1 will show this74 ,hitherto the only spores known are of uniform size1 and there is no evidence that there was any differentiation into small 7male7 and large 7female7 spores such as were found in some of the ,lepidodendrons4 ,in this respect ,sphenophyllum was less specialized than either ,lepidodendron or ,calamites4 ,in the actual sections of ,sphenophyllum cones the numerous sporangia seem massed together in confusion1 but usually some are cut so as to show the attachment of the stalk1 as in fig4 #aag1 st4 ,as the stalk was long and slender1 but a short length of it is usually cut through in any one section1 and to realize their mode of attachment to the axis 7as shown in fig4 #aaf7 it is necessary to study a series of sections4 ,illustration3 ,fig4 #aag4--,part of ,cone of ,sphenophyllum1 showing sporangia sp1 some of which are cut so as to show a part of their stalks st4 ,b1 ,bract4 7,microphoto47 ,of the other plants belonging to the group1 ,bowmanites ,rmeri is specially interesting4 ,its sporangia were borne on stalks similar to those of ,sphenophyllum1 but each stalk had two sporangia attached to it4 ,two sporangia are also borne on each stalk in ,s4 fertile4 ,these plants help in elucidating the nature of the stalked sporangia of ,sphenophyllum1 for they seem to indicate a direct comparison between them and the sporophylls of the ,equisetales4 ,there is1 further1 another plant1 of which we only know the cone1 of still greater importance4 ,this cone 7,cheirostrobus7 is1 however1 so complex that it would take far too much space to describe it in detail4 ,even a diagram of its arrangements is extraordinarily elaborate4 ,to the specialist the cone is peculiarly fascinating1 for its very complexity gives him great scope for weaving theories about it2 but for our purposes most of these are too abstruse4 ,illustration3 ,fig4 #aah4--;,a1 ,diagram of ,three-lobed ,bract from ,cone of ,cheirostrobus4 a1 ,axis2 br1 the three sterile lower lobes of the bract2 sp1 the three upper sporophyll-like lobes1 to each of which were attached four sporangia ,s4 ,b1 ,part of the above seen in section longitudinal to the axis4 7,modified from ,scott47 ,its most important features are the following4 ,round the axis were series of scales1 twelve in each whorl1 and each scale was divided into an upper and a lower portion1 each of which again divided into three lobes4 ,the lower three of each of these scale groups were sterile and bractlike1 comparable1 perhaps1 with the bracts in fig4 #aaf2 while the upper three divisions were stalks round each of which were four sporangia4 ,each sporophyll segment thus resembled the sporophyll of ,calamites1 while the long sausage-shaped sporangia themselves were more like those of ,lepidodendron4 ,in fig4 #aah is a diagram of a trilobed bract with its three attached sporophylls4 ,round the axis were very numerous whorls of such bracts1 and as the cone was large there were enormous numbers of spore sacs4 ,a point of interest is the character of the wood of the main axis1 which is similar to that of ,lepidodendron in many respects1 being a ring of centripetally developed wood with twelve projecting external points of protoxylem4 ,this cone#ac is the most complex fructification of any of the known ,pteridophytes1 whether living or fossil1 which alone ensures it a special importance1 though for our purpose the mixed affinities it shows are of greater interest4 ,to mention some of its characters3--,the individual segments of the sporophylls1 each bearing four sporangia1 are comparable with those of ,calamites1 while the individual sporangia and the length of the sporophyll stalk are similar in appearance to those of ,lepidodendron4 ,the wood of the main axis also resembles that of a typical ,lepidodendron4 ,the way the vascular bundles of the bract pass out from the axis1 and the way the stalks bearing the sporangia are attached to the sterile part of the bracts1 are like the corresponding features in ,sphenophyllum1 and still more like ,bowmanites4 ,many other points of comparison are to be found in these plants1 but without going into further detail enough has been indicated to support the conclusion that ,cheirostrobus is a very important clue to the affinities of the ,sphenophyllales and early ,pteridophytes4 ,it is indeed considered to have belonged to an ancient stock of plants1 from which the ,equisetace1 and ,sphenophylla1 and possibly also the ,lycopods all sprang4 ,sphenophyllum1 ,bowmanites1 and ,cheirostrobus1 a series of forms that became extinct in the ,palozoic1 remote in their structure from any living types1 whose existence would have been entirely unsuspected but for the work of fossil botany1 are yet the clues which have led to a partial solution of the mysteries surrounding the present-day ,lycopods and ,equisetums1 and which help to bridge the chasm between these remote and degenerate families4 ,,chapter ,,xvii ,,past ,,histories ,,of ,,plant ,,families ,x4 ,the ,lower ,plants ,in the plant world of to-day there are many families including immense numbers of species whose organization is simpler than that of the groups hitherto considered4 ,taken all together they form1 in fact1 a very large proportion of the total number of living species1 though the bulk of them are of small size1 and many are microscopic4 ,these 8lower plants0 include all the mosses1 and the flat green liverworts1 the lichens1 the toadstools1 and all the innumerable moulds and parasites causing plant diseases1 the green weeds growing in water1 and all the seaweeds1 large and small1 in the sea1 the minute green cells growing in crevices of the bark of trees1 and all the similar ones living by millions in water4 ,truly a host of forms with an endless variety of structures4 ,yet when we turn to the fossil representatives of this formidable multitude1 we find but few4 ,indeed1 of the fossil members of all these groups taken together we know less that is of importance and real interest than we do of any single family of those hitherto considered4 ,the reasons for this dearth of fossils of the lower types are not quite apparent1 but one which may have some bearing on it is the difficulty of mineralization4 ,it is self-evident that the more delicate and soft-walled any structure is the less chance has it of being preserved without decay long enough to be fossilized4 ,as will have been understood from ,chapter ,,ii1 even when the process of fossilization took place1 geologically speaking1 rapidly1 it can never have been actually accomplished quickly as compared with the counter processes of decay4 ,hence all the lower plants1 with their soft tissue and lack of wood and strengthening cells1 seem on the face of it to stand but little chance of petrifaction4 ,there is much in this argument1 but it is not a sufficient explanation of the rarity of lower plant fossils4 ,all through the preceding chapters mention has been made of very delicate cells1 such as pith1 spores1 and even germinating spores 7see fig4 #dg1 p4 #fh71 with their most delicate outgrowing cells4 ,if then such small and delicate elements from the higher plants are preserved1 why should not many of the lower plants 7some of which are large and sturdy7 be found in the rocks8 ,as regards the first group1 the mosses1 it is probable that they did not exist in the ,palozoic period1 whence our most delicately preserved fossils are derived4 ,there seems much to support the view that they have evolved comparatively recently although they are less highly organized than the ferns4 ,quite recently experiments have been made with their near allies the liverworts1 and those which were placed for one year under conditions similar to those under which plant petrifaction took place1 were found to be perfectly preserved at the end of the period2 though they would naturally decay rapidly under usual conditions4 ,this shows that ,bryophyte cells are not peculiarly incapable of preservation as fossils1 and adds weight to the negative evidence of the rocks1 strengthening the presumption of their late origin4 ,that some of the lower plants1 among the very lowest and simplest1 can be well preserved is shown in the case of the fossil fungi which often occur in microscopic sections of palozoic leaves1 where they infest the higher plants as similar parasitic species do to-day4 ,we must now bring forward the more important of the facts known about the fossils of the various groups of lower plants4 ,bryophytes4--,mosses4 ,of this family there are no specimens of any age which are so preserved as to show their microscopical structure4 ,of impressions there are a few from various beds which show1 with more or less uncertainty in most cases1 stems and leaves of what appear to be mosses similar to those now extant1 but they nearly all lack the fructifications which would determine them with certainty4 ,these impressions go by the name of ,muscites1 which is a dignified cloak for ignorance in most cases4 ,the few which are quite satisfactory as impressions belong to comparatively recent rocks4 ,liverworts are similarly scanty1 and there is nothing among them which could throw any light on the living forms or their evolution4 ,the more common are of the same types as the recent ones1 and are called ,marchantites1 specimens of which have been found in beds of various ages1 chiefly1 however1 in the more recent periods of the earth's history4 ,it is of interest to note that among all the delicate tissue which is so well preserved in the 8coal balls0 and other palozoic petrifactions1 there are no specimens which give evidence of the existence of mosses at that time4 ,it is not unlikely that they may have evolved more recently than the other groups of the 8lower0 plants4 ,charace4--,members of this somewhat isolated family 7,stoneworts7 are better known1 as they frequently occur as fossil casts4 ,this is probably due to their character1 for even while alive they tend to cover their delicate stems and leaves1 and even fruits1 with a limy incrustation4 ,this assists fossilization to some degree1 and fossil ,charas are not uncommon4 ,usually they are from the recently deposited rocks1 and the earliest true ,charas date only to the middle of the ,mesozoic4 ,an interesting occurrence is the petrifaction of masses of these plants together1 which indicate the existence of an ancient pool in which they must have grown in abundance at one time4 ,a case has been described where masses of ,chara are petrified where they seem to have been growing1 and in their accumulations had gradually filled up the pond till they had accumulated to a height of #h feet4 ,the plants1 however1 have little importance from our present point of view4 ,fungi4--,of the higher fungi1 namely1 8toadstools01 we have no true fossils4 ,some indications of them have been found in amber1 but such specimens are so unsatisfactory that they can hardly afford much interest4 ,illustration3 ,fig4 #aai4--,the ,hyph of ,fungi ,parasitic on a ,woody ,tree c1 ,cells of host2 h1 hyph of fungus1 with dividing cell walls4 ,the lower fungi1 however1 and in particular the microscopic and parasitic forms1 occur very frequently1 and are found in the ,coal ,measure fossils4 ,penetrating the tissues of the higher plants1 their hosts1 the parasitic cells are often excellently preserved1 and we may see their delicate hyph wandering from cell to cell as in fig4 #aai1 while sometimes there are attached swollen cells which seem to be sporangia4 ,from the ,palozoic we get leaves with nests of spores of the fungus which had attacked and spotted them as so many do to leaves to-day 7see fig4 #abj74 ,what is specially noticeable about these plants is their similarity to the living forms infesting the higher plants of the present day4 ,already in the ,palozoic the sharp distinction existed between the highly organized independent higher plants and their simple parasites4 ,the higher plants have changed profoundly since that time1 stimulated by ever-changing surroundings1 but the parasites living within them are now much as they were then1 just sufficiently highly organized to rob and reproduce4 ,a form of fungus inhabitant which seems to be useful to the higher plant appears also to have existed in ,palozoic times1 viz4 ,mycorhiza4 ,in the roots of many living trees1 particularly such as the ,beech and its allies1 the cells of the outer layers are penetrated by many fungal forms which live in association with the tree and do it some service at the same time as gaining something for themselves4 ,this curious1 and as yet incompletely understood physiological relation between the higher plants and the fungi1 existed so far back as the ,palozoic period1 from which roots have been described whose cells were packed with minute organisms apparently identical with ,mycorhiza4 ,illustration3 ,fig4 #abj4--;,fossil ,leaf l with ,nests of ,infesting ,fungal ,spores f on its lower side ,alg4--,green ,alg 7pond weeds74 ,many impressions have been described as alg from time to time1 numbers of which have since been shown to be a variety of other things1 sometimes not plants at all4 ,other impressions may really be those of alg1 but hitherto they have added practically nothing to our knowledge of the group4 ,several genera of alg coat themselves with calcareous matter while they are alive1 much in the same way as do the ,charas1 and of these1 as is natural1 there are quite a number of fossil remains from ,tertiary and ,mesozoic rocks4 ,this is still more the case in the group of the ,red ,alg 7seaweeds71 of which the calcareous-coated genera1 such as ,corallina and others1 have many fossil representatives4 ,these plants appear so like corals in many cases that they were long held to be of animal nature4 ,the genus ,lithothamnion now grows attached to rocks1 and is thickly encrusted with calcareous matter4 ,a good many species of this genus have been described among fossils1 particularly from the ,tertiary and ,cretaceous rocks4 ,as the plant grew in association with animal corals1 it is not always very easy to separate it from them4 ,brown ,alg 7seaweeds7 have often been described as fossils4 ,this is very natural1 as so many fossils have been found in marine deposits1 and when among them there is anything showing a dark1 wavy impression1 it is usually described as a seaweed4 ,and possibly it may be one1 but such an impression does not lead to much advance in knowledge4 ,from the early ,palozoic rocks of both ,europe and ,america a large fossil plant is known from the partially petrified structure of its stem4 ,there seem to be several species1 or at least different varieties of this1 known under the generic name ,nematophycus4 ,specimens of this genus are found to have several anatomical characters common to the big living seaweeds of the ,laminaria type1 and it is very possible that the fossils represent an early member of that group4 ,in none of these petrified specimens1 however1 is there any indication of the microscopic structure of reproductive organs1 so that the exact nature of the fossils is not determinable4 ,it is probable that though perhaps allied to the ,laminarias they belong to an entirely extinct group4 ,an interesting and even amusing chapter might be written on all the fossils which look like alg and even have been described as such4 ,the minute river systems that form in the moist mud of a foreshore1 if preserved in the rocks 7as they often are1 with the ripples and raindrops of the past71 look extraordinarily like seaweeds--as do also countless impressions and trails of animals4 ,in this portion of the study of fossils it is better to have a healthy scepticism than an illuminating imagination4 ,diatoms1 with their hard siliceous shells1 are naturally well preserved as fossils 7see fig4 #aba71 for even if the protoplasm decays the mineral coats remain practically unchanged4 ,diatoms to-day exist in great numbers1 both in the cold water of the polar regions and in the heat of hot springs4 ,often1 in the latter1 one can see them actually being turned into fossils4 ,in the ,yellowstone ,park they are accumulating in vast numbers over large areas1 and in some places have collected to a thickness of #f feet4 ,at the bottoms of freshwater lakes they may form an almost pure mud of fine texture1 while on the floor of deep oceans there is an ooze of diatoms which have been separated from the calcareous shells by their greater powers of resistance to solution by salt water4 ,illustration3 ,fig4 #aba4--;,diatom showing the ,double ,siliceous ,coat ,there are enormous numbers of species now living1 and of fossils from the ,tertiary and ,upper ,mesozoic rocks2 but1 strangely enough1 though so numerous and so widely distributed1 both now and in these past periods1 they have not been found in the earlier rocks4 ,in one way the diatoms differ from ordinary fossils4 ,in the latter the soft tissues of the plant have been replaced by stone1 while in the former the living cell was enclosed in a siliceous case which does not decompose1 thus resembling more the fossils of animal shells4 ,bacteria are so very minute that it is impossible to recognize them in ordinary cases4 ,in the matrix of the best-preserved fossils are always minute crystals and granules that may simulate bacterial shapes perfectly4 ,bacillus and ,micrococcus of various species have been described by ,french writers1 but they do not carry conviction4 ,as was stated at the beginning of the chapter1 from all the fossils of all the lower-plant families we cannot learn much of prime importance for the present purpose4 ,yet1 as the history of plants would be incomplete without mention of the little that is known1 the foregoing pages have been added4 ,,chapter ,,xviii ,,fossil ,,plants ,,as ,,records ,,of ,,ancient ,,countries ,the land which to-day appears so firm and unchanging has been under the sea many times1 and in many different ways has been united to other land masses to form continents4 ,at each period1 doubtless1 the solid earth appeared as stable as it is now1 while the country was as well characterized1 and had its typical scenery1 plants1 and animals4 ,we know what an important feature of the character of any present country is its flora2 and we have no reason to suspect that it was ever less so than it is to-day4 ,indeed1 in the ages before men interfered with forest growth1 and built their cities1 with their destructive influences1 the plants were relatively more important in the world landscape than they are to-day4 ,as we go back in the periods of geological history we find the plants had an ever-increasing area of distribution4 ,to-day most individual species and many genera are limited to islands or parts of continents1 but before the ,glacial epoch many were distributed over both ,america and ,europe4 ,in the ,mesozoic ,ginkgo was spread all over the world1 and in the present epoch it was confined to ,china and ,japan till it was distributed again by cultivation2 while in the ,palozoic period ,lepidodendron seemed to stretch wellnigh from pole to pole4 ,the importance of the relation of plant structure to the climate and local physical conditions under which it was growing cannot be too much insisted upon4 ,modern biology and ecology are continually enlarging and rendering more precise our views of this interrelation1 so that we can safely search the details of anatomical structure of the fossil plants for sidelights on the character of the countries they inhabited and their climates4 ,it has been remarked already that most of the fossils which we have well preserved1 whether of plants or animals1 were fossilized in rocks which collected under sea water2 yet it was also noted that of marine plants we have almost no reliable fossils at all4 ,how comes this seeming contradiction8 ,the lack of marine plant fossils probably depends on their easily decomposable nature1 while the presence of the numerous land plants resulted from their drifting out to sea in streams and rivers1 or dropping into the still salt marshes where they grew4 ,hence1 in the rocks deposited in a sea1 we have the plants preserved which grew on adjacent lands4 ,in fresh water1 also1 the plants of the neighbourhood were often fossilized2 but actually on the land itself but little was preserved4 ,the winds and rains and decay that are always at work on a land area tend to break down and wash away its surface1 not to build it up4 ,there are many different details which are used in determining the evidence of a fossil plant4 ,where leaf impressions are preserved which exhibit a close similarity to living species 7as often happens in the ,tertiary period71 it is directly assumed that they lived under conditions like those under which the present plants of that kind are living2 while1 if the anatomy is well preserved 7as in the ,palozoic and several ,mesozoic types71 we can compare its details with that of similar plants growing under known conditions1 and judge of the climate that had nurtured the fossil plant while it grew4 ,previous to the present period there was what is so well known as the ,glacial epoch4 ,in the earthy deposits of this age in which fossils are found plants are not uncommon4 ,they are of the same kind as those now growing in the cold regions of the ,arctic circle1 and on the heights of hills whose temperature is much lower than that of the surrounding lowlands4 ,glacial epochs occurred in other parts of the world at different times2 for example1 in ,south ,africa1 in the ,permo-,carboniferous period1 during which time the fossils indicate that the warmth-loving plants were driven much farther north than is now the case4 ,it is largely from the nature of the plant fossils that we know the climate of ,england at the time preceding the ,glacial epoch4 ,impressions of leaves and stems1 and even of fruits1 are abundant from the various periods of the ,tertiary4 ,many of them were ,angiosperms 7see ,chap4 ,,viii71 and were of the families and even genera which are now living1 of which not a few belong to the warm regions of the earth1 and are subtropical4 ,it is generally assumed that the fossils related to1 or identical with1 these plants must therefore have found in ,tertiary ,northern ,europe a much warmer climate than now exists4 ,not only in ,northern ,europe1 but right up into the ,arctic circle1 such plants occur in ,tertiary rocks1 and even if we had not their living representatives with which to compare them1 the large size and thin texture of their leaves1 their smoothness1 and a number of other characteristics would make it certain that the climate was very much milder than it is at present1 though the value of some of the evidence has been overestimated4 ,from the ,tertiary we are dependent chiefly on impressions of fossils2 anatomical structure would doubtless yield more details1 but even as it is we have quite enough evidence to throw much light on the physiography of the ,tertiary period4 ,the causes for such marked changes of climate must be left for the consideration of geologists and astronomers4 ,plants are passive1 driven before great climatic changes1 though they have a considerable influence on rainfall1 as has been proved repeatedly in ,india in recent times4 ,from the more distant periods it is the plants of the ,carboniferous1 whose structure we know so well1 that teach us most4 ,although there is still very much to be done before knowledge is as complete as we should wish1 there are sufficient facts now discovered to correct several popular illusions concerning the ,palozoic period4 ,the 8deep1 all-enveloping mists1 through which the sun's rays could scarcely penetrate01 which have taken the popular imagination1 appear to have no foundation in fact4 ,there is nothing in the actual structure of the plants to indicate that the light intensity of the climate in which they grew was any less than it is in a smoke-free atmosphere to-day4 ,look at the 8shade leaves0 of any ordinary tree1 such as a ,lime or ,maple1 and compare them with those growing in the sunlight1 even on the same tree4 ,they are larger and softer and thinner4 ,to absorb the same amount of energy as the more brilliantly lighted leaves1 they must expose a larger surface to the light4 ,hence if the ,coal ,measure plants grew in very great shade1 to supply their large growth with the necessary sun energy we should expect to find enormous spreading leaves4 ,but what is the fact8 ,no such large leaves are known4 ,calamites and ,lepidodendron1 the commonest and most successful plants of the period1 had narrow simple leaves with but a small area of surface4 ,they were1 in fact1 leaves of the type we now find growing in exposed places4 ,the ferns had large divided leaves1 but they were finely lobed and did not expose a large continuous area as a true 8shade leaf0 does2 while the height of their stems indicates that they were growing in partial shade--at least1 the shade cast by the small-leaved ,calamites and ,lepidodendrons which overtopped them4 ,indeed there is no indication from geological evidence that so late as ,palozoic times there was any great abnormality of atmosphere1 and from the internal evidence of the plants then growing there is everything to indicate a dry or physiologically dry#ad sunny condition4 ,of the plant fossils from the ,coal ,measures we have at least two types4 ,one1 those commonly found in nodules in the coal itself2 and the other1 nodules in the rocks above the coal which had drifted from high lands into the sea4 ,the former are the plants which actually formed the coal itself1 and from their internal organization we see that these plants were growing with partly submerged roots in brackish swamps4 ,their roots are those of water plants 7see p4 #aej1 young root of ,calamite71 but their leaves are those of the 8protected0 type with narrow surface and various devices for preventing a loss of water by rapid transpiration4 ,if the water they grew in had been fresh they would not have had such leaves1 for there would have been no need for them to economize their water1 but1 as we see in bogs and brackish or salt water to-day 7which is physiologically usable in only small quantities by the plant71 plants even partly submerged protect their exposed leaves from transpiring largely4 ,there are details too numerous to mention in connection with these coal-forming plants which go to prove that there were large regions of swampy ground near the sea where they were growing in a bright atmosphere and uniform climate4 ,extensive areas of coal1 and geological evidence of still more extensive deposits1 show that in ,europe in the ,coal ,measure period there were vast flats1 so near the sea level that they were constantly being submerged and appearing again as dbris drifted and collected over them4 ,such a land area must have differed greatly from the ,europe now existing1 in all its features4 ,but the whole continent did not consist of these flats2 there were hills and higher ground1 largely to the north-east1 on which a dry land flora grew1 a flora where several of the ,pteridosperms and ,cordaites with its allies were the principal plants4 ,these plants have leaves so organized as to suggest that they grew in a region where the climate was bright and dry4 ,a fossil flora which has aroused much interest1 particularly among geologists1 is that known as the ,glossopteris flora4 ,this ,palozoic flora has in general characters similar to those of the ,european ,permo-,carboniferous1 but it has special features of its own1 in particular the genus ,glossopteris and also the genera ,phyllotheca and ,schizoneura4 ,these genera1 with a few others1 are characteristic of the ,permo-,carboniferous period in the regions in the ,southern ,hemisphere now known by the names of ,australasia1 ,south ,africa1 and ,south ,america1 and in ,india4 ,these regions1 at that date1 formed what is called by geologists 8,gondwanaland04 ,in the rocks below those containing the plants there is evidence of glacial conditions1 and it is not impossible that this great difference in climate accounts for the differences which exist between the flora of the ,gondwanaland region and the ,northern ,hemisphere4 ,unfortunately we have not microscopically preserved specimens of the ,glossopteris flora1 which could be compared with those of our own ,palozoic4#ae ,to describe in detail the series of changes through which the seas and continents have passed belongs to the realm of pure geology4 ,here it is only necessary to point out how the evidence from the fossil plants may afford much information concerning these continents1 and as our knowledge of fossil anatomy and of recent ecology increases1 their evidence will become still more weighty4 ,even now1 had we no other sources of information1 we could tell from the plants alone where in the past continents were snow and ice1 heat and drought1 swamps and hilly land4 ,however different in their systematic position or scale of evolutional development1 plants have always had similar minute structure and similar physiological response to the conditions of climate and land surface1 so that in their petrified cells are preserved the histories of countries and conditions long past4 ,,chapter ,,xix ,,conclusion ,in the stupendous pageant of living things which moves through creation1 the plants have a place unique and vitally important4 ,yet so quietly and so slowly do they live and move that we in our hasty motion often forget that they1 equally with ourselves1 belong to the living and evolving organisms4 ,when we look at the relative structures of plants divided by long intervals of time we can recognize the progress they make2 and this is what we do in the study of fossil botany4 ,we can place the salient features of the flora of ,palozoic and ,mesozoic eras in a few pages of print1 and the contrast becomes surprising4 ,but the actual distance in time between these two types of plants is immense1 and must have extended over several million years2 indeed to speak of years becomes meaningless1 for the duration of the periods must have been so vast that they pass beyond our mental grasp4 ,in these periods we find a contrast in the characters of the plants as striking as that in the characters of the animals4 ,whole families died out1 and new ones arose of more complex and advanced organization4 ,but in height and girth there is little difference between the earliest and the latest trees2 there seems a limit to the possible size of plants on this planet1 as there is to that of animals1 the height of mountains1 or the depth of the sea4 ,the 8higher plants0 are often less massive and less in height than the lower--,man is less in stature than was the ,dinosaur--and though by no legitimate stretch of the imagination can we speak of brain in plants1 there is an unconscious superiority of adaptation by which the more highly organized plants capture the soil they dominate4 ,it has been noted in the previous chapters that so far back as the ,coal ,measure period the vegetative parts of plants were in many respects similar to those of the present1 it was in the reproductive organs that the essential differences lay4 ,naturally1 when a race 7as all races do7 depends for its very existence on the chain of individuals leading from generation to generation1 the most important items in the plant structures must be those mechanisms concerned with reproduction4 ,it is here that we see the most fundamental differences between living and fossil plants1 between the higher and the lower of those now living1 between the forest trees of the present and the forest trees of the past4 ,the wood of the palozoic ,lycopods was in the quality and extent and origin of its secondary growth comparable with that of higher plants still living to-day--yet in the fruiting organs how vast is the contrast6 ,the ,lycopods1 with simple cones composed of scales in whose huge sporangia were simple single-celled spores2 the flowering plants1 with male and female sharply contrasted yet growing in the same cone 7one can legitimately compare a flower with a cone71 surrounded by specially coloured and protective scales1 and with the 8spore0 in the tissue of the young seed so modified and changed that it is only in a technical sense that comparison with the ,lycopod spore is possible4 ,to study the minute details of fossil plants it is necessary to have an elaborate training in the structure of living ones4 ,in the preceding chapters only the salient features have been considered1 so that from them we can only glean a knowledge similar to the picture of a house by a ,japanese artist--a thing of few lines4 ,even from the facts brought together in these short chapters1 however1 it cannot fail to be evident how large a field fossil botany covers1 and with how many subjects it comes in touch4 ,from the minute details of plant anatomy and evolution pure and simple to the climate of departed continents1 and from the determination of the geological age of a piece of rock by means of a blackened fern impression on it to the chemical questions of the preservative properties of sea water1 all is a part of the study of 8fossil botany04 ,to bring together the main results of the study in a graphic form is not an easy task1 but it is possible to construct a rough diagram giving some indication of the distribution of the chief groups of plants in the main periods of time 7see fig4 #abb74 ,such a diagram can only represent the present state of our imperfect knowledge2 any day discoveries may extend the line of any group up or down in the series1 or may connect the groups together4 ,it becomes evident that so early as the ,palozoic there are nearly as many types represented as in the present day1 and that in fact everything1 up to the higher ,gymnosperms1 was well developed 7for it is hard indeed to prove that ,cordaites is less highly organized than some of the present ,gymnosperm types71 but flowering plants and also the true cycads are wanting1 as well as the intermediate ,mesozoic ,bennettitales4 ,the peculiar groups of the period were the ,pteridosperm series1 connecting links between fern and cycad1 and the ,sphenophyllums1 connecting in some measure the ,lycopods and ,calamites4 ,with them some of the still living groups of ferns1 ,lycopods1 and ,equisetace were flourishing1 though all the species differed from those now extant4 ,this shows us how very far from the beginning our earliest information is1 for already in the ,palozoic we have a flora as diversified as that now living1 though with more primitive characters4 ,illustration3 ,fig4 #abb4--;,diagram showing the relative distribution of the main groups of plants through the geological eras4 ,the dotted lines connecting the groups and those in the pre-,carboniferous are entirely theoretical1 and merely indicate the conclusions reached at present4 ,the size of the surface of each group roughly indicates the part it played in the flora of each period4 ,those with dotted surface bore seeds1 the others spores4 ,in ,mesozoic times the most striking group is that of the ,cycads and ,bennettitales1 the latter branch suggesting a direct connection between the fern-cycad series and the flowering plants4 ,this view1 so recently published and upheld by various eminent botanists1 is fast gaining ground4 ,indeed1 so popular has it become among the specialists that there is a danger of overlooking the real difficulties of the case4 ,the morphological leap from the leaves and stems of cycads to those of the flowering plants seems a much more serious matter to presuppose than is at present recognized4 ,as is indicated in the diagram1 the groups do not appear isolated by great unbridged gaps1 as they did even twenty years ago4 ,by means of the fossils either direct connections or probable lines of connection are discovered which link up the series of families4 ,at present the greatest gap now lies hedging in the ,moss family1 and1 as was mentioned 7p4 #afc71 fossil botany cannot as yet throw much light on that problem owing to the lack of fossil mosses4 ,this glimpse into the past suggests a prophecy for the future4 ,evolution having proceeded steadily for such vast periods is not likely to stop at the stage reached by the plants of to-day4 ,what will be the main line of advance of the plants of the future1 and how will they differ from those of the present8 ,we have seen in the past how the differentiation of size in the spores resulted in sex1 and in the higher plants in the modifications along widely different lines of the male and female2 how the large spore 7female7 became enclosed in protecting tissues1 which finally led up to true seeds 7see p4 #ge71 while the male being so temporary had no such elaboration4 ,as the seed advances it becomes more and more complex1 and when we reach still higher plants further surrounding tissues are pressed into its service and it becomes enclosed in the carpel of the highest flowering plants4 ,after that the seed itself has fewer general duties1 and instead of those of the ,gymnosperms with large endosperms collecting food before the embryo appears1 small ovules suffice1 which only develop after fertilization is assured4 ,the various families of flowering plants have gone further1 and the whole complex series of bracts and fertile parts which make up a flower is adapted to ensure the crossing of male and female of different individuals4 ,the complex mechanisms which seem adapted for 8cross fertilization0 are innumerable1 and are found in the highest groups of the flowering plants4 ,but some have gone beyond the stage when the individual flowers had each its device1 and accomplished its seed-bearing independently of the other flowers on the same branch4 ,these have a combination of many flowers crowded together into one community1 in which there is specialization of different flowers for different duties4 ,in such a composite flower1 the ,daisy for example1 some are large petalled and brightly coloured to attract the pollen-carrying insects1 some bear the male organs only1 and others the female or seed-producing4 ,here1 then1 in the most advanced type of flowering plant we get back again to the separation of the sexes in separate flowers2 but these flowers are combined in an organized community much more complex than the cones of the ,gymnosperms1 for example1 where the sexes are separate on a lower plane of development4 ,it seems possible that an important group1 if not the dominant group1 of flowering plants in the future will be so organized that the individual flowers are very simple1 with fewer parts than those of to-day1 but that they will be combined in communities of highly specialized individuals in each flower head or cluster4 ,as well as this1 in other species the minute structure of the vital organs may show a development in a direction contrary to what has hitherto seemed advance4 ,until recently flowers and their organs have appeared to us to be specialized in the more advanced groups on such lines as encourage 8cross fertilization04 ,in 8cross fertilization01 in fact1 has appeared to lie the secret of the strength and advance of the races of plants4 ,but modern cytologists have found that many of the plants long believed to depend on cross fertilization are either self-fertilized or not fertilized at all6 ,they have passed through the period when their complex structures for ensuring cross fertilization were used1 and though they retain these external structures they have taken to a simpler method of seed production1 and in some cases have even dispensed with fertilization of the egg cell altogether4 ,the female vitality increased1 the male becomes superfluous4 ,it is simpler and more direct to breed with only one sex1 or to use the pollen of the same individual4 ,many flowers are doing this which until recently had not been suspected of it4 ,we cannot yet tell whether it will work successfully for centuries to come or is an indication of 8race senility04 ,whether in the epochs to come flowering plants will continue to hold the dominant position which they now do is an interesting theoretical problem4 ,flowers were evolved in correlation with insect pollination4 ,one can conceive of a future1 when all the earth is under dominion of man1 in which fruits will be sterilized for man's use1 as the banana is now1 and seed formation largely replaced by gardeners' 8cuttings04 ,in those plants which are now living where the complex mechanisms for cross-fertilization have been superseded by simple self-fertilization1 the external parts of the more elaborate method are still produced1 though they are apparently futile4 ,in the future these vestigial organs will be discarded1 or developed in a more rudimentary form 7for it is remarkable how organs that were once used by the race reappear in members of it that have long outgrown their use71 and the morphology of the flower will be greatly simplified4 ,thus we can foresee on both sides much simplified individual flowers--in the one group the reduced individuals associating together in communities the members of which are highly specialized1 and in the other the solitary flowers becoming less elaborate and conspicuous1 as they no longer need the assistance of insects 7the cleistogamic flowers of the ,violet1 for example1 even in the present day bend toward the earth1 and lack all the bright attractiveness of ordinary flowers71 and perhaps finally developing underground1 where the seeds could directly germinate4 ,in the vegetative organs less change is to be expected1 the examples from the past lead us to foresee no great difference in size or general organization of the essential parts1 though the internal anatomy has varied1 and probably will vary1 greatly with the whole evolution of the plant4 ,but one more point and we must have done4 ,why do plants evolve at all8 ,why did they do so through the geological ages of the past1 and why should we expect them to do so in the future8 ,the answer to this question must be less assured than it might have been even twenty years ago1 when the magnetism of ,darwin's discoveries and elucidations seemed to obsess his disciples4 8,response to environment0 is undoubtedly a potent factor in the course of evolution1 but it is not the cause of it4 ,there seems to be something inherent in life1 something apparently 7though that may be due to our incomplete powers of observation7 apart from observable factors of environment which causes slight spontaneous changes1 mutations1 and some individuals of a species will suddenly develop in a new direction in one or other of their parts4 ,if1 then1 this places them in a superior position as regards their environment or neighbours1 it persists1 but if not1 those individuals die out4 ,the work of a special branch of modern botany seems clearly to indicate the great importance of this seemingly inexplicable spontaneity of life4 ,in environment alone the thoughtful student of the present cannot find incentive enough for the great changes and advances made by organisms in the course of the world's history4 ,the climate and purely physical conditions of the ,coal ,measure period were probably but little different from those in some parts of the world to-day1 but the plants themselves have fundamentally changed4 ,true1 their effect upon each other must be taken into account1 but this is a less active factor with plants than with men1 for we can imagine nothing equivalent to citizenship1 society1 and education in the plant communities1 which are so vital in human development4 ,it seems to have been proved that plants and animals may1 at certain unknown intervals1 8mutate02 and mutation is a fine word to express our recent view of one of the essential factors in evolution4 ,but it is a cloak for an ignorance avowedly less mitigated than when we thought to have found a complete explanation of the causes of evolution in 8environment04 ,in a sketch such as the present1 outlines alone are possible1 detail cannot be elaborated4 ,if it has suggested enough of atmosphere to show the vastness of the landscape spreading out before our eyes back into the past and on into the future1 the task has been accomplished4 ,there are many detailed volumes which follow out one or other special line of enquiry along the highroads and by-ways of this long traverse in creation4 ,if the bird's-eye view of the country given in this book entices some to foot it yard by yard under the guidance of specialists for each district1 it will have done its part4 ,while to those who will make no intimate acquaintance with so far off a land it presents a short account by a traveller1 so that they may know something of the main features and a little of the romance of the fossil world4 ,,appendix ,i ,,list ,,of ,,requirements ,,for ,a ,,collecting ,,expedition ,in order to obtain the best possible results from an expedition1 it is well to go fossil hunting in a party of two1 four1 or six persons4 ,large parties tend to split up into detachments1 or to waste time in trying to keep together4 ,each individual should have strong suitable clothes1 with as many pockets arranged in them as possible4 ,the weight of the stones can thus be distributed over the body1 and is not felt so much as if they were all carried in a knapsack4 ,each collector should also provide himself with-- ,a satchel or knapsack1 preferably of leather or strong canvas1 but not of large size1 for when the space is limited selection of the specimens is likely to be made carefully4 ,one or two hammers4 ,if only one is carried1 it should be of a fair size with a square head and strong straight edge4 ,one chisel1 entirely of metal1 and with a strong straight cutting edge4 ,soft paper to wrap up the more delicate fossils1 in order to prevent them from scraping each other's surfaces2 and one or two small cardboard boxes for very fragile specimens4 ,a map of the district 7preferably geologically coloured74 ,localities should be noted in pencil on this1 indicating the exact spot of finds4 ,for general work the one-inch survey map suffices1 but for detailed work it is necessary to have the six-inch maps of important districts4 ,a small notebook4 ,few notes are needed1 but those few must be taken on the spot to be reliable4 ,a pencil or fountain pen1 preferably both4 ,a penknife1 which1 among other things1 will be found useful for working out very delicate fossils4 ,,appendix ,,ii ,,treatment ,,of ,,specimens #a4 ,the commonest form in which fossils are collected is that which has been described as impression material 7see p4 #ab74 ,in many cases these will need no further attention after the block of stone on which they lie has been chipped into shape4 ,in chipping a block down to the size required it is best to hold it freely in the left hand1 protecting the actual specimen with the palm where possible1 and taking the surplus edges away by means of short sharp blows from the hammer1 striking so that only small pieces come away with each blow4 ,for delicate specimens it is wise to leave a good margin of the matrix round the specimen1 and to do the final clearing with a thin-bladed penknife1 taking away small flakes of the stone with delicate taps on the handle of the knife4 ,specimens from fine sandstones1 shales1 and limestones are usually thoroughly hard and resistant1 and are then much better if left without treatment2 by varnishing and polishing them many amateur collectors spoil their specimens1 for a coat of shiny varnish often conceals the details of the fossil itself4 ,impressions of plants on friable shales1 on the other hand1 or those which have a tendency to peel off as they dry1 will require some treatment4 ,in such cases the best substance to use is a dilute solution of size1 in which the specimen should soak for a short period while the liquid is warm 7not hot71 after which it should be slightly drained and the size allowed to dry in4 ,the congealed substance then holds the plant film on to the rock surface and prevents the rock from crumbling away1 while it is almost invisible and does not spoil the plant with any excessive glaze4 #b4 ,for specimens of casts the same treatment generally applies1 though they are more apt to separate completely from the matrix after one or two sharp blows1 and thus save one the work of picking out the details of their structure4 #c4 ,those blocks which contain petrifactions1 and can therefore be made to show microscopic details1 will require much more treatment4 ,in some cases mere polishing reveals much of the structure--such1 for instance1 were the 8,staarsteine0 of the ,german lapidaries1 where the axis and rootlets of a fossil like a treefern show their very characteristic pattern distinctly4 ,as a rule1 however1 it is better1 and for any detailed work it is essential1 to cut thin sections transversely across and longitudinally through the axis of the specimen and to grind them down till they are so transparent that they can be studied through the microscope4 ,the cutting can be done on a lapidary's wheel1 where a revolving metal disc set with diamond powder acts as a knife4 ,the comparatively thin slice thus obtained is fastened on to glass by means of hard ,canada balsam1 and rubbed down with carborundum powder till it is thin enough4 ,the process1 however1 is very slow1 and an amateur cannot get good results without spending a large amount of time and patience over the work which would be better spent over the study of the plant structures themselves4 ,therefore it is usually more economical to send specimens to be cut by a professional1 if they are good enough to be worth cutting at all1 though it is often advisable to cut through an unpromising block to see whether its preservation is such as would justify the expense4 ,in the case of true 8coal balls0 much can be seen on the cut surface of a block1 particularly if it be washed for a minute in dilute hydrochloric acid and then in water1 and then dried thoroughly4 ,the acid acts on the carbonates of which the stone is largely composed1 and the treatment accentuates the black-and-white contrast in the petrified tissues 7see fig4 #aj74 ,after lying about for a few months the sharpness of the surface gets rubbed off1 as the acid eats it into very delicate irregularities which break and form a smearing powder2 but in such a case all that is needed to bring back the original perfection of definition is a quick wash of dilute acid and water4 ,if the specimens are not rubbed at all the surface is practically permanent4 ,blocks so treated reveal a remarkable amount of detail when examined with a strong hand lens1 and form very valuable museum specimens4 ,the microscope slides should be covered with glass slips 7as they would naturally be if purchased71 and studied under the microscope as sections of living plants would be4 ,microscopic slides of fossils make excellent museum specimens when mounted as transparencies against a window or strong light1 when a magnifying glass will reveal all but the last minuti of their structure4 #d4 ,labelling and numbering of specimens is very important1 even if the collection be but a small one4 ,as well as the paper label giving full details1 there should be a reference number on every specimen itself4 ,on the microscope slides this can be cut with a diamond pencil1 and on the stones sealing wax dissolved in alcohol painted on with a brush is perhaps the best medium4 ,on light-coloured close-textured stones ink is good1 and when quite dry can even be washed without blurring4 ,the importance of marking the stone itself will be brought home to one on going through an old collection where the paper labels have peeled or rubbed off1 or their wording been obliterated by age or mould4 ,a notebook should be kept in which the numbers are entered1 with a note of all the items on the paper label1 and any additional details of interest4 ,,appendix ,,iii ,,literature ,a short list of a few of the more important papers and books to which a student should refer4 ,the innumerable papers of the specialists will be found cited in these1 so that1 as they would be read only by advanced students1 there is no attempt to catalogue them here4 ,carruthers1 ,w41 8,on ,fossil ,cycadean ,stems from the ,secondary ,rocks of ,britain10 published in the ,transactions of the ,linnean ,society1 vol4 xxvi1 #ahgj4 99,geikie1 ,a41 ,a ,text-,book of ,geology1 vols4 i and ii1 ,london1 #aijc4 ,grand',eury1 ,c41 8,flore ,carbonifre du dpartement de la ,loire et du centre de la ,france01 published in the ,mmoirs de l',acadmie des ,sciences1 ,paris1 vol4 xxiv1 #ahgg4 99,kidston1 ,r41 ,catalogue of the ,palozoic ,plants in the ,department of ,geology and ,palontology of the ,british ,museum1 ,london1 #ahhf4 99,lapworth1 ,c41 ,an ,intermediate ,text-,book of ,geology1 twelfth edition1 ,london1 #ahhh4 ,laurent1 ,l41 8,les ,progrs de la palobotanique angiospermique dans la dernire decade01 ,progressus ,rei ,botanic1 vol4 i1 ,heft #b1 pp4 #cai-fh1 ,jena1 #aijg4 ,lindley1 ,j41 and ,hutton1 ,w41 ,the ,fossil ,flora of ,great ,britain1 #c vols41 published in ,london1 #ahca-g4 ,lyell1 ,c41 ,principles of ,geology and ,the ,student's ,lyell1 edited by ,j4 ,w4 ,judd1 ,london1 #ahif4 ,oliver1 ,f4 ,w41 and ,scott1 ,d4 ,h41 8,on the ,structure of the ,palozoic ,seed1 ,lagenostoma ,lomaxi01 published in the ,transactions of the ,royal ,society1 series ,b1 vol4 cxcvii1 ,london1 #aijd4 ,renault1 ,b41 ,cours de ,botanique fossile1 ,paris1 #ahhb1 #d vols4 ,renault1 ,b41 ,bassin ,houiller et ,permien d',autun et d',epinac1 ,atlas and ,text1 #ahic-f1 ,paris4 99,scott1 ,d4 ,h41 ,studies in ,fossil ,botany1 ,london1 second edition1 #aiji4 ,scott1 ,d4 ,h41 8,on the ,structure and ,affinities of ,fossil ,plants from the ,palozoic ,rocks4 ,on ,cheirostrobus1 a ,new ,type of ,fossil ,cone from the ,lower ,carboniferous ,strata40 ,published in the ,philosophical ,transactions of the ,royal ,society1 vol4 clxxxix1 ,b1 #ahig4 99,seward1 ,a4 ,c41 ,fossil ,plants1 vol4 i1 ,cambridge1 #ahih4 ,seward1 ,a4 ,c41 ,catalogue of the ,mesozoic ,plants in the ,department of ,geology of the ,british ,museum1 ,parts ,i and ,,ii1 ,london1 #ahid-e4 99,solms-,laubach1 ,graf zu1 ,fossil ,botany 7translation from the ,german71 ,oxford1 #ahia4 ,stopes1 ,m4 ,c41 and ,watson1 ,d4 ,m4 ,s41 8,on the ,structure and ,affinities of the ,calcareous ,concretions known as #8,coal ,balls'01 published in the ,philosophical ,transactions of the ,royal ,society1 vol4 cc4 99,stopes1 ,m4 ,c41 ,the ,study of ,plant ,life for ,young ,people1 ,london1 #aijf4 99,watts1 ,w4 ,w41 ,geology for ,beginners1 ,london1 #aije 7second edition74 ,wieland1 ,g4 ,r41 ,american ,fossil ,cycads1 ,carnegie ,institute1 #aijf4 ,williamson1 ,w4 ,c41 ,a whole series of publications in the ,philosophical ,transactions of the ,royal ,society from #ahga to #ahia1 and three later ones jointly with ,dr4 ,scott2 the series entitled 8,on the ,organization of the ,fossil ,plants of the ,coal ,measures01 ,memoir ,i1 ,,ii1 c4 ,zeiller1 ,r41 lments de ,palobotanique1 ,paris1 #aijj4 99,zittel1 ,k41 ,handbuch der ,palontologie1 vol4 ii2 ,palophytologie1 by ,schimper ,schenk1 ,mnchen and ,leipzig1 #aijj4 ,those marked 99 would be found the most useful for one beginning the subject4 ,,glossary ,some of the more technical terms about which there might be some doubt1 as they are not always accompanied by explanations in the text1 are here briefly defined4 ,anatomy4--,the study of the details and relative arrangements of the internal features of plants2 in particular1 the relations of the different tissue systems4 ,bracts4--,organs of the nature of leaves1 though not usual foliage leaves4 ,they often surround fructifications1 and are generally brown and scaly1 though they may be brightly coloured or merely green4 ,calcareous4--,containing earthy carbonates1 particularly calcium carbonate 7chalk74 ,cambium4--,narrow living cells1 which are constantly dividing and giving rise to new tissues 7see fig4 #cc1 p4 #eg74 ,carbonates1 as used in this book1 refer to the combinations of some earthy mineral1 such as calcium or magnesium1 combined with carbonic acid gas and oxygen1 formula ,ca,c,o#c1 ,mg,c,o#c1 c4 ,carpel4--,the closed structure covering the seeds which grow attached to it4 ,the 8husk0 of a peapod is a carpel4 ,cell4--,the unit of a plant body4 ,fundamentally a mass of living protoplasm with its nucleus1 surrounded in most cases by a wall4 ,mature cells show many varieties of shape and organization4 ,see ,chapter ,,vi1 p4 #ed4 ,centrifugal4--,wood or other tissues developed away from the centre of the stem4 ,see fig4 #fe1 p4 #ig4 ,centripetal4--,wood or other tissues developed towards the centre of the stem4 ,see fig4 #fe1 p4 #ig4 ,chloroplast4--,the microscopic coloured masses1 usually round1 green bodies1 in the cells of plants which are actively assimilating4 ,coal ,balls4--,masses of carbonate of calcium1 magnesium1 c41 generally of roundish form1 which are found embedded in the coal1 and contain petrified plant tissues4 ,see p4 #bh4 ,concretions4--,roundish mineral masses1 formed in concentric layers1 like the coats of an onion4 ,see p4 #bg4 ,cotyledons4--,the first leaves of an embryo4 ,in many cases packed with food and filling the seed4 ,see fig4 #eh4 ,cross ,fertilization4--,the fusion of male and female cells from different plants4 ,cuticle4--,a skin of a special chemical nature which forms on the outer wall of the epidermis cells4 ,see p4 #ed1 fig4 #ba4 ,earth ,movements4--,the gradual shifting of the level of the land1 and the bending and contortions of rocks which result from the slow shrinking of the earth's surface1 and give rise to earthquakes and volcanic action4 ,embryo4--,the very young plant1 sometimes consisting of only a few delicate cells1 which results from the divisions of the fertilized egg cell4 ,the embryo is an essential part of modern seeds1 and often fills the whole seed1 as in a bean1 where the two fleshy masses filling it are the two first leaves of the embryo4 ,see fig4 #eh1 p4 #gg4 ,endodermis4--,the specialized layer of cells forming a sheath round the vascular tissue4 ,see p4 #ee4 ,endosperm4--,the many-celled tissue which fills the large 8spore0 in the ,gymnosperm seed1 into which the embryo finally grows4 ,see fig4 #eg4 ,epidermis4--,outer layer of cells1 which forms a skin1 in the multicellular plants4 ,see fig4 #ba1 p4 #ed4 ,fruit4--,essentially consisting of a seed or seeds1 enclosed in some surrounding tissues1 which may be only those of the carpel1 or may also be other parts of the flower fused to it4 ,thus a peapod is a fruit1 containing the peas1 which are seeds4 ,gannister4--,a very hard1 gritty rock found below some coal seams4 ,see p4 #be4 ,genus4--,a small group within a family which includes all the plants very like each other1 to which are all given the same 8surname02 e4g4 ,pinus montana1 ,pinus sylvestris1 ,pinus ,pinaster1 c4 c41 are all members of the genus ,pinus1 and would be called 8pine trees0 in general 7see 8,species074 ,hyph4--,the delicate elongated cells of ,fungi4 ,molecule4--,the group of chemical elements1 in a definite proportion1 which is the basis of any compound substance2 e4g4 two atoms of hydrogen and one atom of oxygen form a molecule of water1 ,h#b,o4 ,a lime carbonate molecule 7see definition of 8,carbonate07 is represented as ,ca,c,o#c4 ,monostelic4--,a type of stem that contains only one stele4 ,morphology4--,the study of the features of plants1 their shapes and relations1 and the theories regarding the origin of the organs4 ,nucellus4--,the tissue in a ,gymnosperm seed in which the large 8spore0 develops4 ,see figs4 #ee and #ef1 p4 #gf4 ,nucleus4--,the more compact mass of protoplasm in the centre of each living cell1 which controls its growth and division4 ,see fig4 #ag1 n4 ,palobotany4--,the study of fossil plants4 ,palontology4--,the study of fossil organisms1 both plants and animals4 ,petiole4--,the stalk of a leaf1 which attaches it to the stem4 ,phloem4--,commonly called 8bast04 ,the elongated vessel-like cells which conduct the manufactured food4 ,see p4 #eg4 ,pollen ,chamber4--,the cavity inside a ,gymnosperm seed in which the pollen grains rest for some time before giving out the male cells which fertilize the egg-cell in the seed4 ,see p4 #gf4 ,polystelic4--,a type of stem that appears1 in any transverse section1 to contain several steles4 ,see note on the use of the word on p4 #fc4 ,protoplasm4--,the colourless1 constantly moving mass of finely granulated1 jelly-like substance1 which is the essentially living part of both plants and animals4 ,rock4--,used by a geologist for all kinds of earth layers4 ,clay1 and even gravel1 are 8rocks0 in a geological sense4 ,roof1 of a coal seam4 ,the layers of rock--usually shale1 limestone1 or sandstone--which lie just above the coal4 ,see p4 #bd4 ,sclerenchyma4--,cells with very thick walls1 specially modified for strengthening the tissues4 ,see fig4 #bh1 p4 #ef4 ,seed4--,essentially consisting of a young embryo and the tissues round it1 which are enclosed in a double coat4 ,see definition of 8,fruit04 ,shale4--,a fine-grained soft rock1 formed of dried and pressed mud or silt1 which tends to split into thin sheets1 on the surface of which fossils are often found4 ,species4--,individuals which in all essentials are identical are said to be of the same species4 ,as there are many variations which are not essential1 it is sometimes far from easy to draw the boundary between actual species4 ,the specific name comes after that of the genus1 e4g4 ,pinus montana is a species of the genus ,pinus1 as is also ,pinus sylvestris4 ,see 8,genus04 ,sporangium4--,the saclike case which contains the spores4 ,see figs4 #eb and #ec1 p4 #ge4 ,spore4--,a single cell 7generally protected by a cell wall7 which has the power of germinating and reproducing the plant of which it is the reproductive body4 ,see p4 #ge4 ,sporophyll4--,a leaf or part of a leaf which bears spores or seeds1 and which may be much or little modified4 ,stele4--,a strand of vascular tissue completely enclosed in an endodermis4 ,see p4 #fb4 ,stigma4--,a special protuberance of the carpel in flowering plants which catches the pollen grains4 ,stomates4--,breathing pores in the epidermis1 which form as a space between two curved liplike cells4 ,see fig4 #bc1 p4 #ed4 ,tetrads4--,groups of four cells which develop by the division of a single cell called the 8mother cell04 ,spores and pollen grains are nearly always formed in this way4 ,see p4 #ge4 ,tracheid4--,a cell specially modified for conducting or storing of water1 often much elongated4 ,the long wood cells of ,ferns and ,gymnosperms are tracheids4 ,underclay4--,the fine clay found immediately below some coal seams4 ,see p4 #bd4 ,vascular ,tissue4--,the elongated cells which are specialized for conduction of water and semifluid foodstuffs4 ,,footnotes #a,my book was entirely written before the second edition of ,scott's ,studies appeared1 which1 had it been available1 would have tempted me to escape some of the labour several of the chapters of this little book involved4 #b,the student would do well to read up the general geology of this very interesting subject4 ,such books as ,lyell's ,principles of ,geology1 ,geikie's textbooks1 and many others1 provide information about the process of 8mountain building0 on which the form of our coalfields depends4 ,a good elementary account is to be found in ,watt's ,geology for ,beginners1 p4 #if et seq4 #c,see note on p4 #bh4 #d,this refers only to the 8coal-ball0-bearing seams2 there are many other coals which have certainly collected in other ways4 ,see ,stopes ,watson1 ,appendix1 p4 #ahg4 #e;,for a detailed list of the strata refer to ,watts1 p4 #bai 7see ,appendix74 #f,though the ,angiosperm was not then evolved1 the ,gymnosperm stem has distinct vascular bundles arranged as are those of the ,angiosperm1 the difference here lies in the type of wood cells4 #g,the gametophyte generation 7represented in the ferns by the prothallium on which the sexual organs develop7 alternates with the large1 leafy sporophyte4 ,refer to ,scott's volume on ,flowerless ,plants 7see ,appendix7 for an account of this alternation of generations4 #h,material recently obtained by the author and ,dr4 ,fujii in ,japan does contain some true petrifactions of ,angiosperms and other plant debris4 ,the account of these discoveries has not yet been published4 #i;,a fuller account of the ,angiospermic flora can be had in ,french1 in ,m4 ,laurent's paper in ,progressus ,rei ,botanic4 ,see ,appendix for reference4 #aj;,from the ,cretaceous deposits of ,north ,america several fossil forms 7,brachyphyllum1 ,protodammara7 are described which show clear affinities with the family as it is now constituted4 7,see ,hollick and ,jeffrey2 reference in the ,appendix47 #aa,the addition of -oxylon to the generic name of any living type indicates that we are dealing with a fossil which closely resembles the living type so far as we have information from the petrified material4 #ab,see reference in the ,appendix to this richly illustrated volume4 #ac;,for fuller description of this interesting cone1 see ,scott's ,studies1 p4 #aad et seq4 #ad;,a brackish swampy land is physiologically dry1 as the plants cannot use the water4 ,see ,warming's ,oecology of ,plants1 ,english edition1 for a detailed account of such conditions4 ,for a simple account see ,stopes' ,the ,study of ,plant ,life1 p4 #agj4 #ae,the student interested in this special flora should refer to ,arber's ,british ,museum ,catalogue of the ,fossil ,plants of the ,glossopteris ,flora4 ,,index 7,italicized numbers refer to illustrations7 ,abietine1 #hh1 #hi1 #ij4 -- family characters of1 #ia4 ,alg1 #dd1 #dg1 #afe4 -- brown1 #aff4 -- green1 #afe4 -- red1 #afe4 ,alnus1 #he4 ,amber1 #ag4 ,amentifer1 #hd4 ,anatomy of fossil plants1 likeness in detail to that of living plants1 #ec et seq4 -- -- -- -- differences in detail from that of living plants1 #fi et seq4 ,andromeda1 #hd4 ,angiosperms1 comparison with ,bennettitales1 #ajc4 -- early history of1 #gi et seq4 -- general distribution of in time1 #agg4 -- later evolution of1 #agh4 -- male cell of1 #eb4 ,araliace1 #he4 ,araucare1 #hh1 #ij1 #aaa4 -- description of1 #ij4 -- primitive characters of1 #hi4 ,araucarioxylon1 #ic1 #ie4 ,arber1 #agc4 ,archocalamites1 #aeb4 ,artocarpace1 #he4 ,asterochlaena1 #abf1 #abg1 #hf1 #hi4 ,bacillus1 #afg4 ,bacteria1 #afg4 ,baiera1 #aja4 ,bast1 #eg1 #cb4 ,bennettitales1 #dd1 #ajb1 #aca4 -- general distribution of in time1 #agg4 ,bennettites1 #ajc et seq4 -- external appearance of1 #ajc4 -- flower-like nature of fructification1 #ajh4 -- fructification of1 #ajd1 #ga1 #aje1 #gb4 -- seed of1 #ajf1 #gc4 ,bertrand1 #b4 ,betula1 #he4 ,bignonia1 #hd4 ,botryopteride1 #abe1 #acb4 -- description of group1 #abe4 -- fructifications of1 #abh4 -- petioles of1 #abg1 #hi4 -- stem anatomy of1 #abf1 #hf1 #hg4 -- wood of1 #abh1 #ij4 ,botryopteris1 #abf1 #abg4 -- axis with petiole1 #abg1 #hh1 #hi4 ,bowmanites ,rmeri1 #aeh1 #afj4 ,brachyphyllum1 #hi4 ,brongniart1 #b4 ,bryophytes1 #afc4 ,calamites1 #adg1 #aed1 #aeg1 #aei1 #afj1 #aga4 -- branch of1 #adg1 #ajd4 -- casheana1 #aeb4 -- cone of1 #aej1 #aji1 #aea1 #aaj4 -- leaf of1 #adi1 #ajg4 -- node of1 #adi1 #ajf4 -- spores of1 #aeb1 #aaa4 -- young roots of1 #aej1 #ajh4 -- young stem of1 #adh1 #aje4 ,cambium1 #eg1 #cc1 #fe1 #dc1 #ff1 #dd4 ,carbon1 film of representing decayed plant1 #ab4 ,carbonate of magnesium1 #bj4 ,carbonates of lime1 #ai4 ,carpels1 modified leaves1 #gh4 ,carruthers1 #ahf4 ,casts of fossil plants1 #h1 #i1 #b1 #aj1 #c1 #d1 #aa1 #ab4 -- of seeds1 #aa1 #ab4 -- treatment of specimens of1 #ahd4 ,casuarina1 #hc4 ,cells1 similarity of living and fossil types of1 #ec4 -- principal types of1 #ec et seq41 #bb-cc4 ,cell wall1 #dg1 #ag4 ,centrifugal wood1 #ig1 #fe4 ,centripetal wood1 #ig1 #fe1 #aaf4 ,chara1 #af4 ,charace1 #afc4 ,cheirostrobus1 #aei1 #aah1 #afj4 ,chloroplast1 #dg1 #ag4 ,coal1 origin of1 #bi et seq4 -- of different ages1 #cc4 -- seams in the rocks1 #bd1 #ac1 #ad4 -- vegetable nature of1 #be et seq4 -- importance of1 #ag1 ,chap4 ,,iii1 p4 #bb et seq4 8,coal balls01 #ah1 #ai1 #aj1 #bj1 #ba1 #bb1 #bg1 #ae1 #afc1 #ahe4 -- -- mass of1 in coal1 #bh1 #af4 ,coal ,measures1 climate of1 #agb4 ,companion cells1 #eg1 #cb4 ,concretions1 #ba1 #bb1 #bg1 #ae1 #bh4 -- concentric banding in1 #bg1 #ae4 ,conducting tissue in higher plants1 #di1 #ai1 #ej1 #bj4 ,coniferales1 conflicting observations among1 #df4 -- general distribution in time1 #agg4 -- male cell of1 #eb4 ,corallina1 #aff4 ,cordaite1 #ci-hh1 #aab4 -- comparison of fructifications with those of ,taxe1 #ie4 -- description of family1 #ib4 -- general distribution in time1 #agg4 ,cordaites1 #dj1 #ajg1 #agf4 -- fructification of1 #ie1 #if1 #fd4 -- internal cast of stem1 #aj1 #d1 #ic1 #id1 #ie4 -- leaves of1 once considered to be ,monocotyledons1 #hb1 #ic4 -- leaves of1 #ic1 #fa1 #id1 #fb;,a4 -- possible common origin with ,ginkgo1 #ajb4 -- wood of1 #id1 #fb;,b4 ,cork1 #ef1 #bi4 -- cambium1 #ef1 #bi4 ,cross fertilization1 #agi4 ,cupresse1 #hh1 #ij4 -- description of1 #ia4 ,cycadeoidea1 #ajc4 ,cycads in the ,mesozoic period1 #dj1 #da1 #db1 #aac4 -- description of group1 #aji4 -- general distribution of in time1 #agg4 -- in ,tertiary period1 #he4 -- large size of male cones of1 #aaj4 -- seeds of1 #aab4 -- type of seed of1 #gf1 #eg4 -- wood of1 #aaj4 ,cycas1 #aji1 #aaj1 #gd4 -- seed-bearing sporophyll of1 #aaa4 -- seeds of1 #aab1 #gf4 -- comparison with ,ginkgo seeds1 #aab4 ,darwin1 #aha4 ,diatoms1 #afg1 #aba4 ,dicotyledons1 #da1 #dd1 #gi4 -- relative antiquity of1 #ha1 #hb4 -- seed type of1 #gg1 #eh4 ,differentiation1 commencement of in simple plants1 #dh4 -- of tissues in higher plants1 #di1 #ai1 #ej et seq41 #bj4 ,embryo of ,ginkgo1 #ajj4 -- in seeds1 #gf1 #eg1 #gg1 #eh4 -- of ,bennettites1 #ajf1 #gc4 ,endodermis1 #ee1 #bf1 #fa4 ,environment1 #aha1 #ahb4 ,epidermal tissues1 #ed1 #ba1 #bb1 #bc1 #abe4 ,epidermis cells1 fossil impressions of1 #ac1 #ad1 #h1 #ei1 #cd1 #abe4 ,equisetales1 #dd4 -- general distribution of in time1 #agg4 ,equisetites1 #adf1 #ajc4 ,equisetum1 #i1 #ch1 #dj1 #dd1 #ade1 #adi1 #aeb4 -- underground rhizomes of1 #dc4 ,eucalyptus1 #hc4 ,europe1 #hg1 #ajb4 -- ancient climates of1 #agj4 ,evolution1 #dc4 -- in plants1 various degrees of in the organs of the same plant1 #de et seq4 ,evolution in plants1 cause of1 #aha4 -- -- -- suggestions as to possible future lines of1 #agh4 ,expedition1 requirements for collecting1 #ahc4 ,extinct families1 #dd4 ,ferns1 sporangia of1 #fg1 #de4 -- connection with ,pteridosperms1 #abc4 -- description of group1 #abd4 -- fructifications of among fossils1 #aca1 #acb1 #ib4 -- general distribution of in time1 #agg4 -- germinating spores of1 #fh1 #dg4 ,ficus1 #hc4 ,flotsam1 #f4 ,flowering plant1 anatomy of stem1 #di1 #ai4 ,formation of rocks1 key to processes1 #f4 ,fossil plants1 indications of ancient climates and conditions1 #afh4 -- -- diagram illustration the distribution of1 #agg1 #abb4 ,fungi1 fossils of1 #afd4 -- parasitic1 #aai1 #afd1 #afe1 #abj4 ,gamopetal1 #hd4 ,gannister1 #be1 #ad4 ,geikie1 #ahf4 ,ginkgo1 leaf impression1 #ad1 #g1 #ajj1 #fi4 -- comparison with ,cycas seeds1 #aab4 -- distribution in the past1 #afh4 -- embryo of1 #ajj4 -- epidermis of fossil1 #ad1 #h1 #ajj4 -- foliage of1 #ii1 #ff4 -- only living species of genus1 #ih1 #gj4 -- possible common origin with ,cordaites1 #ajb4 -- ripe seed of1 #ii1 #fg4 -- section of seed of1 #ajj1 #fh4 -- seed structure of1 #gf1 #eg4 -- similarity to ,cordaites1 #if4 ,ginkgoace1 #hh4 ,ginkgoales1 #hh1 #ih4 -- description of group1 #ih4 -- general distribution in time1 #agg4 ,glacial epoch1 #agj4 ,glossopteris1 #agc4 ,glyptostrobus1 #hf4 ,gondwanaland1 #agc4 ,grand',eury1 #ahf4 ,gum1 #ag4 ,gymnosperms1 #ch1 #da1 #dd1 #hf1 #agf1 #agi4 -- connection with ,pteridosperms1 #abd4 -- general distribution in time1 #agg4 -- relations between the groups of1 #hh1 #hi1 #ij4 ,hairs1 #ed1 #bb1 #gj4 -- special forms among fossils1 #gj4 ,heterangium1 #aai1 #abb1 #abc1 #abg4 -- foliage of1 #abj4 -- stem of1 #abj1 #ha4 ,hollick and ,jeffrey1 #hi4 ,horsetails1 description of group1 #ade4 ,hutton1 #b4 ,impression1 form of fossil1 #e1 #ab1 #ac1 #f1 #ad1 #g1 #ae1 #hj1 #ha1 #ei1 #fj4 -- treatment of specimens of1 #ahd4 ,investigators of fossil plants1 #b4 ,iron sulphide1 #bj4 ,jet1 #ag4 ,juglandace1 #hc4 ,kauri pine1 #ic4 ,kew ,gardens1 #ih4 ,kidston1 #ahf4 ,labelling of specimens1 #ahe4 ,lagenostoma1 #gf1 #ef1 #aah1 #aai1 #hj4 ,laminaria1 #aff4 ,lapworth1 #ahf4 ,latex cells1 #ee1 #bg4 ,laurace1 #he4 ,laurent1 #ahf4 ,leaves1 starch manufacture in cells of1 #eh4 -- fossil leaf anatomy1 #ei1 #cd4 -- general similarity of living and fossil1 #eh4 ,lepidocarpon1 #ada1 #ajj4 ,lepidodendron1 #i1 #aj1 #c1 #ba1 #ab1 #fg1 #df1 #gb1 #ge1 #acd1 #add1 #ade1 #aeg1 #afj1 #aga4 -- anatomy of stem of1 #acf1 #acg1 #ie1 #ach1 #if1 #aci1 #ig4 -- comparison of reproductive organs with those of living lycopods1 #fg1 #df4 ,lepidodendron1 description of1 #acd4 -- distribution in the past1 #agg4 -- fructification of1 #aci1 #adj1 #ih1 #ada1 #ii4 -- huge stumps of1 #acd1 frontispiece4 -- leaf bases1 #aj1 #c1 #ace1 #ic4 -- leaf traces of1 #aci1 #ig4 -- peculiar fructification of1 #ge1 #ed4 -- petrifaction of leaves1 #ba1 #ab4 -- rootlike organs of1 #fi4 -- secondary thickening in1 #gj1 #dh1 #ga1 #di4 -- selaginoides1 stem of1 #acg1 #ie4 -- wood of1 #gj1 #dh1 #ga1 #di4 ,liliace1 #hb4 ,limestone1 #g1 #a1 #bd1 #be1 #cf4 ,lindley1 #b1 #ahf4 ,literature on fossil plants1 #ahf4 ,lithothamnion1 #aff4 ,liverworts1 #afc4 ,lycopods1 #ch1 #dj1 #db1 #dd1 #fg1 #acc1 #age4 -- description of group1 #acc4 -- general distribution in time1 #agg4 -- reproductive organs of1 #fg1 #df4 -- secondary wood in fossil1 #gj1 #dh1 #ga1 #di4 ,lyell1 #ahf4 ,lyginodendron1 #aae1 #aaf1 #abb4 -- anatomy of stem of1 #aaf1 #gh;,a4 -- petioles of1 #aag1 #aah1 #gi4 -- roots of1 #aag1 #gh;,b4 -- seeds of1 #aah1 #aai1 #hj4 ,magnolia1 #hc4 ,marattia1 #acj4 ,marattiace1 #abe1 #abi4 -- appearance of1 #acj4 -- description of group1 #abi4 ,marchantites1 #afc4 ,medullosa1 #gb1 #gc1 #aai1 #abj1 #aba1 #hb1 #hc1 #abb1 #abc4 -- foliage of1 #aba1 #hc4 -- probable seeds of1 #aba4 -- steles of1 #gb1 #ej1 #gc1 #ea1 #abj4 ,mesozoic1 character of flora1 #dj4 ,metaxylem1 #eg1 #ca4 ,mycorhiza1 #afe4 ,micrococcus1 #afg4 ,monocotyledons1 #da1 #dd1 #gi4 -- relative antiquity of1 #ha1 #hb4 ,monostelic anatomy1 #fc1 #abf4 ,mosses1 scarcity of fossils of1 #afb4 ,mosses1 fossils of1 #afc4 ,mountain building1 from deposits under water1 #f4 -- -- slow and continuous changes1 #ce4 ,muscites1 #afc4 ,mutation1 #aha4 ,nematophycus1 #aff4 ,neuropteris1 leaf impression1 #f1 #ac4 -- foliage of ,medullosa1 #abb4 -- with seed attached1 #abb1 #he4 ,nipa1 #he4 ,nodules1 #ae1 #af1 #i4 ,nucleus1 #dg1 #ag4 ,oliver1 #ahg4 ,osmunda1 #abe4 ,ovule1 word unsuitable for palaeozoic 8seeds01 #gg4 ,palisade cells1 #ee1 #be4 -- tissue in leaves1 #eh4 -- -- -- fossil leaf1 #ei1 #cd4 ,palms1 #he4 ,parenchyma1 #ee1 #bd4 ,petrifaction of cells1 #d4 ,petrifactions1 #ag4 -- of forest dbris1 #ah4 -- treatment of specimens of1 #ahd4 ,phyllotheca1 #agc4 ,plant1 parts of1 the same in living and fossil1 #ei4 -- world1 main families in1 #dd4 ,platanus1 #hc4 ,polypodiace1 #abd4 ,polystelic anatomy1 #fc1 #gb4 ,populus1 #hc1 #he4 ,poroxyle1 #hh4 -- description of group of1 #if4 ,poroxylon1 anatomy of1 #ig1 #aaf4 ,primitive plants1 #df4 ,primofilices1 #acb4 ,protococcoide1 #dg1 #ag4 ,protodammara1 #hi4 ,protoplasm1 #dg4 ,protostele1 #fb1 #gj4 ,protoxylem1 #eg1 #ca4 ,psaronius1 #abi1 #acj4 -- stem anatomy of1 #aca1 #ia4 ,pteridophytes1 development of secondary wood in fossil forms of1 #gb4 ,pteridosperms1 #dd1 #ajd1 #aad1 #aca4 -- description of group1 #aad et seq4 -- general distribution of in time1 #agg4 -- summary of characters of1 #abc4 ,pteris aurita1 #fb4 ,quarries1 #g1 #a4 ,quercus1 #hc1 #he4 ,race senility1 #ahj4 ,ranales1 #ajc4 ,renault1 #b1 #aef1 #ahg4 ,reproductive organs1 likeness between those of living and fossil plants1 #fg1 #de1 #df4 -- -- peculiar characters of some from the ,palozoic1 #gd4 -- -- simplicity of essential cells of1 #eb4 ,rocks1 persistence of mineral constituents1 #cf4 -- fossils varying in according to the geological age1 #cg et seq4 ,roof of coal seam1 #bd1 #ac1 #be1 #ad4 ,roots1 likeness of structure in living and fossil1 #fj1 #ce4 ,salix1 #hc4 ,sambucus1 #hd4 ,schizoneura1 #agc4 ,sclerenchyma1 #ef1 #bf1 #ei1 #cd4 ,scott1 #b1 #afj1 #ahg4 ,secondary wood1 development of in fossil members of families now lacking it1 #gb4 ,seeds1 series of types from spores to seeds1 #ge1 #gf1 #eb-eh4 -- position on the plant1 #gg1 #gh4 -- ,tertiary impressions of1 #hj1 #ha1 #fj4 ,selaginella1 #ge1 #acc1 #acd4 -- with four spores in a sporangium1 #ge1 #ec4 ,sequoia1 #hf4 ,seward1 #ahg4 8,shade leaves01 #aga4 ,shale1 #g1 #a1 #aa1 #bd1 #be1 #cf4 ,sieve tubes1 #eg1 #cb4 ,sigillaria1 #adb1 #ade4 ,sigillaria1 cast of leaf bases1 #i1 #b1 #add1 #ajb4 -- description of1 #add4 ,silica1 #ag4 ,silicified wood1 #ag1 #hj1 #hg4 ,solms ,laubach1 #b1 #ahg4 ,specimens1 treatment of1 #ahd4 ,sphenophyllales1 #dd1 #aec4 -- description of1 #aec4 -- general distribution in time1 #agg4 ,sphenophyllum1 #dd1 #aec1 #aed1 #afj4 -- cone of1 #aeg1 #aaf4 -- fertile1 #aeh4 -- impression of foliage1 #aed1 #aab4 -- plurifoliatum1 #aec4 -- sporangia of1 #aeh1 #aag4 -- stem anatomy1 #aee1 #aac1 #aef1 #aad4 -- stem in coal ball1 #bj4 -- wood of1 #aef1 #aad1 #aae4 ,sphenopteris1 leaf impression1 #aa1 #e4 -- foliage of ,pteridosperms1 #aae1 #gg4 ,sporangium of ferns1 #fg1 #de4 -- of lycopods1 #fg1 #df4 -- of pteridophytes1 #ge1 #eb1 #ec1 #ed4 ,spores1 germinating1 in fossil sporangia1 #fh1 #dg4 -- peculiar structures among palozoic examples of1 #gd4 -- series of types from 8spores0 to 8seeds01 #ge1 #gf1 #eb-eh4 -- tetrads of1 #ge1 #eb1 #ec1 #ed4 ,sporophyll1 #ge1 #eb1 #ec1 #ed4 ,stangeria1 #aaj4 ,stele1 modifications of1 #fb1 #cf-db4 ,stems1 external similarity in living and fossil1 #fj4 ,sternbergia1 cast of1 #aj1 #d4 -- pith cast of ,cordaites1 #ic4 ,stigmaria1 #fi1 #adb1 #adc1 #add1 #ade4 -- rootlet of1 #adc1 #aja4 ,stomates1 #ed1 #bc4 -- in fossil epidermis1 #ad1 #h4 ,stoneworts1 #afc4 ,synclines1 #bc4 ,taxe1 #hh1 #ij4 -- comparison of fructification with that of ,cordaite1 #ie4 -- description of1 #ib4 ,taxe1 fleshy seeds of1 #hi4 ,taxodium1 #hf4 ,taxus1 #hb4 ,time1 divisions of geological time1 #cd4 ,tracheides for water storage1 #ef1 #cj4 ,tree-ferns1 #acj4 ,trigonocarpus1 #aa1 #gf1 #hb1 #abb1 #hd4 -- once supposed to be a ,monocotyledon1 #hb4 -- probably the seed of ,medullosa1 #aba4 ,tubicaulis1 #abg1 #hi4 ,unexplored world1 #c4 ,unicellular plants1 #dg1 #ag4 -- -- division of cells in1 #dg1 #dh1 #ah4 8,vascular bundles01 relation of to steles1 #fe1 #db4 -- tissue1 #eg1 #ca1 #cb1 #cc1 #ei4 -- -- continued growth of1 #fe1 #dc4 -- -- importance in plant anatomy1 #fa et seq4 ,viburnum1 #hd1 #he4 ,watts1 #ahg4 ,westphalia1 #ai4 ,wieland1 #b1 #ajb1 #ahg4 ,williamson1 #b1 #ahg4 ,williamsonia1 #ajd4 ,wood1 cells composing1 #eg1 #ca4 -- centrifugal development of1 #ig1 #fe4 -- centripetal development of1 #ig1 #fe4 -- parenchyma1 #eg1 #ca4 -- silicified1 #ag1 #hj1 #hg4 -- solid rings of formed by cambium1 #ff1 #dd4 -- vessels of ,angiosperms1 #eh4 ,yellowstone ,park1 #ag1 #afg4 ,yew1 #hb4 ,yucca1 #hb4 ,zeiller1 #b1 #ahg4 ,zittel1 #ahg4 ,zygopteris1 #abg4 ,by the ,same ,author ,the ,study of ,plant ,life for ,young ,people ,demy #hvo1 fully illustrated1 #bs4 #f;d4 net ,nature3 8,of the various books written for children in elementary schools1 ,the ,study of ,plant ,life is quite the most logical and intelligent that we have seen04 ,manchester ,guardian3 8,with great skill the knowledge gained from simple experiments in the classroom or laboratory is made effective4444 ,our old friend the cactus 444 and other exotic wonders are happily relegated to very subordinate parts in these bright and attractive pages40 ,athenum3 8,the author has attained simplicity of language--a more difficult business than writers of textbooks imagine--and as the book is printed in large1 clear type1 we can strongly recommend it to teachers in schools04 ,inquirer3 8,is a delightful book1 beautifully illustrated04 ,scotsman3 8,the book is a charming guide for the youthful botanist or naturalist to the life history of plants1 and it is written with a due regard to the age of those for whom it is intended04 ,knowledge3 8,an excellent book for young people desirous of learning the why and wherefore of plant life04 ,new ,age3 8,we have seen nothing produced on this side of the ,atlantic so good of its kind04 ,new ,phytologist3 8444 may be unhesitatingly pronounced a great success 444 written with a breadth and knowledge he has not met before in an ,english elementary work04 ,,london3 ,,blackie ,,son1 ,limited1 #ej ,,old ,,bailey1 ,e4,c4 ,transcriber's ,notes --,silently corrected a handful of palpable typos4 --,moved footnotes to a section immediately preceding the ,index1 and added an entry for it to the ,contents4 --,slightly reformatted tables to better fit dynamic flow on narrow screens4 --,conjecturally restored one missing subtopic 78,coal1 importance of07 in the ,index4 --,in the text versions1 delimited text in italics by underscores4 --,in the text versions1 included filenames of illustrations1 for more convenient reference 7by another program74