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GLASGOW AND BOMBAY 1910 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 horizon. Until comparatively recent times the rather narrow outlook and the technical difficulties of the study made it one which could only be appreciated by specialists. This has been gradually changed, owing to the detailed anatomical work which it was found possible to do on the carboniferous plants, and which proved to be of great botanical importance. About ten years ago textbooks in English were written, and the subject was included in the work of the honours students of Botany at the Universities. To-day the important bearing of the results of this branch of Science on several others, as well as its intrinsic value, is so much greater, that anyone who is at all acquainted with general science, and more particularly with Botany and Geology, must find much to interest him in it. There is no book in the English language which places this really attractive subject before the non-specialist, and to do so is the aim of the present volume. The two excellent English books which we possess, viz. Seward’s Fossil Plants (of which the first volume only has appeared, and that ten years ago) and Scott’s Studies in Fossil Botany, are ideal for advanced University students. But they are written for students who are supposed to have a previous knowledge of technical botany, and prove very hard or impossible reading for those who are merely acquainted with Science in a general way, or for less advanced students. The inclusion of fossil types in the South Kensington syllabus for Botany indicates the increasing importance attached to palzo- botany, and as vital facts about several of those types are not to be found in a simply written book, the students preparing for the examination must find some difficulty in getting their information. Furthermore, Scott’s book, the only up-to-date one, does not give a complete survey of the subject, but just selects the more impor- tant families to describe in detail. Hence the present book was attempted for the double purpose of presenting the most interesting discoveries and general con- Vv vi PREFACE clusions of recent years, and bringing together the subject as a whole. The mass of information which has been collected about fossil plants is now enormous, and the greatest difficulty in writing this little book has been the necessity of eliminating much that is of great interest. The author awaits with fear and trembling the criticisms of specialists, who will probably find that many things considered by them as particularly interesting or essential have been left out. It is hoped that they will bear in mind the scope and aim of the book. I try to present only the structure raised on the foundation of the accumulated details of specialists’ work, and not to demonstrate brick by brick the exposed foundation. Though the book is not written specially for them, it is probable that University students may find it useful as a general survey of the whole subject, for there is much in it that can only be learned otherwise by reference to innumerable original monographs. In writing this book all possible sources of information have been consulted, and though Scott’s Studies! naturally formed the foundation of some of the chapters on Pteridophytes, the authorities. for all the general part and the recent discoveries are the numerous. memoirs published by many different learned societies here and abroad. | As these pages are primarily for the use of those who have no very technical preliminary training, the simplest language possible which is consistent with a concise style has always been adopted. The necessary technical terms are either explained in the context or in the glossary at the end of the book. The list of the more important authorities makes no pretence of including all the refer- ences that might be consulted with advantage, but merely indicates. the more important volumes and papers which anyone should read who wishes to follow up the subject. All the illustrations are made for the book itself, and I am much obliged to Mr. D. M. S. Watson, B.Sc., for the microphotos of plant anatomy which adorn its pages. The figures and diagram are my own work. This book is dedicated to college students, to the senior pupils. of good schools where the subject is beginning to find a place in the higher courses of Botany, 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 trace. M. C,.STOPES. December, 1909. 1 My book was entirely written before the second edition of Scott’s Studies appeared, which, had it been available, would have tempted me to escape some of the labour several of the chapters of this little book involved. VII. VIIl. IX. XVI. XVII. - XVIIL XIX. Contents INTRODUCTORY - ' s 7 ‘ - ms ~ v . Various KINps oF FossiL PLANTS - “ ‘s * e . COAL, THE MOST IMPORTANT OF PLANT REMAINS . - . THE SEVEN AGES OF PLANT LIFE = P 4 “ : . STAGES IN PLANT EVOLUTION -_ - “ . a : . MINUTE STRUCTURE OF FossiL PLANTs — Likenesses to Living Ones - era) ees Sper eal) Seen ama Oe MINUTE STRUCTURE OF FossiIL PLANTs — Differences from Living Ones - - - - - - PSY, Say SRC Past Histories OF PLANT FAMILIES— (i) Flowering Plants’ - » vs (ii) Higher Gymnosperms ” 9 (iii) Bennettitales - - » 59 (iv) The Cycads - eS ” 3 (v) Pteridosperms :-~— - ” xj (vi) The Ferns - rs E » +s (vii) The Lycopods 9 3 (viii) The Horsetails vs us (ix) Sphenophyllales - 93 (x) The Lower Plants” - FossiL PLANTts AS RECORDS OF. ANCIENT COUNTRIES - CONCLUSION - * ; Fe : z z 2 a z Page Vili CONTENTS APPENDIX I. List oF REQUIREMENTS FOR A COLLECTING EXPEDITION - 183 II]. TREATMENT OF SPECIMENS -_ - - - = = - 184 III. LireRatTure - - - - - - - - - - 186 GLOSSARY - - * - - - ~ - - - 188 INDEX - - “ . = - = - . - 193 ANCIENT PLANTS CHAPTER. | 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 ‘‘dryness” of fossil botany. It is true that all that remains of the once luxuriant vegetation are fragments preserved in stone, fragments which often show little of beauty or value to the un- trained eye; but nevertheless these fragments can tell a story of great interest when once we have the clue to their meaning. The plants which lived when the world was young were not the same as those which live to-day, yet they filled much the same place in the economy of nature, and were as vitally important to the animals then de- pending on them as are the plants which are now in- dispensable to man. To-day the life of the modern plants interests many people, 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 evolution. But all the plants which are now alive are the descendants of those which lived a few years ago, and those again came down through generation after generation from the plants which 1 ‘ 2 ANCIENT PLANTS inhabited the world before the races of men existed. If, therefore, we wish to know and understand the vegeta- tion living to-day we must look into the past histories of the families of plants, and there is no way to do this at once so simple and so direct (in theory) as to examine the remains of the plants which actually lived in that past. Yet when we come to do this practically we encounter many difficulties, which have discouraged all but enthusiasts from attempting the study hitherto, but which in reality need not dismay us. When Lindley and Hutton, in 1831, began to publish their classical book Zhe Fossel Flora of Great Britazn, they could give but isolated fragments of information concerning the fossils they described, and the results of their work threw but little light on the theoretical pro- blems of morphology and classification of living plants. Since then great advance has been made, and now the sum of our knowledge of the subject, though far from complete, is so considerable and has such a far-reaching influence that it is becoming the chief inspiration of several branches of modern botany. Of the many workers who have contributed to this stock of knowledge the foremost, as he was the pioneer in the investigations. on modern lines, is Williamson, who was a professor at Manchester University, and whose monographs and speci- mens are classics to-day. Still living is Dr. Scott, whose greatness is scarcely less, as well as an ever-increasing number of specialists in this country, who are continually making discoveries. Abroad, the chief Continental names. are Renault, Bertrand, Count Solms Laubach, Brongniart, Zeiller; and in America is Dr. Wieland; while there are innumerable other workers in the field who have deepened and widened the channels of information. — The literature on fossil plants. is now vast; so great that to give merely the names of the publications would fill a very large volume. But, like the records left by the plants themselves, most of this literature is unreadable by any but special- INTRODUCTORY 2 ists, and its really vital interest is enclosed in a petrify- ing medium of technicalities. It is to give their results. in a more accessible form that the present volume has. been written. The actual plants that lived and died long ago have left either no trace of their form and character, or but. imperfect fragments of some of their parts embedded in hard rock and often hidden deep in the earth. That such difficulties lie in our way should not discourage us. from attempting to learn all the fossils can teach. Many an old manuscript which is torn and partly destroyed bears a record, the fragments of which are more interest- ing and important than a tale told by a complete new book. The very difficulty of the subject of fossil botany is in itself an incentive to study, and the obstacles to be surmounted before a view of the ancient plants can be seen increase the fascination of the journey. The world of to-day has been nearly explored; but the world, or rather the innumerable world-phases of the past, lie before us practically unknown, bewilderingly enticing in their mystery. These untrodden regions are revealed to us only by the fossils lying scattered through the rocks at our feet, which give us the clues to guide us. along an adventurous path. 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 globe; and among the plants such wonderful monsters have their parallels in the floras ot the past. The trees which are living to-day are very recent in comparison with the ancestors of the families. of lowlier plants, 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 Equise- _tums, which are now humble and dwindling. An ancient giant of the past is seen in the frontispiece, and the great girth of its stem offers a striking contrast to the feeble trailing branches of its living relatives, the Club-mosses 4 ANCIENT PLANTS As we follow their histories we shall see how family after family has risen to dominate the forest, and has in its turn given place to a succeeding group. Some of the families that flourished long since have living descendants of dwarfed and puny growth, others have died out com- pletely, so that their very existence would have been unsuspected had it not been revealed by their broken fragments entombed in the rocks. From the study of the fossils, also, we can discover something of the course of the evolution of the different parts of the plant body, from the changes it has passed through in the countless ages of its existence. Just as the dominant animals of the past had bodies lacking in many of the characters which are most important to the living animals, so did the early plants differ from those around us to-day. It is the comparative study of living and fossil structures which throws the strongest light on the facts and factors of evolution. When the study of fossil organisms goes into minute detail and embraces the fine subtleties of their internal structure, then the student of fossil plants has the ad- vantage of the zoological observer, 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 approach. Under the microscope the most delicate of plant cells, the patterns on their walls, and sometimes even their nuclei can be recognized as clearly as if they were living tissues. The value of this is immense, because the external appearance of leaves and stems is often very deceptive, and only when both external appearance and internal structure are known can a real estimate of the character of the plant be made. In the following chapters.a number of photo- graphs taken through the microscope will show some of the cell structure from fossil plants. Such figures as fig. 11 and fig. 96, for example, illustrate the excel- lence of preservation which is often found in petrified plant tissues. Indeed, the microscope becomes an essen- INTRODUCTORY 5 tial part of the equipment of a fossil botanist; as it is to a student of living plants. But for those who are not intending to specialize on the subject micro-photographs will illustrate sufficient detail, while in most modern museums some excellently preserved specimens are ex- hibited which show their structure if examined with a magnifying glass. e recognize to-day the effect the vegetation of a district has on its scenery, even on its more fundamental nature; and we see how the plants keep in close har- mony with the lands and waters, the climates and soils of the places they inhabit. So was it in thespast. Hence the fossil plants of a district will throw much light on its physical characters during the epoch when they were living, and from their evidence it is possible to build up a picture of the conditions of a region during the epochs of its unwritten history. 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 fossils. Not only to the botanist is the subject of value, the geologist is equally concerned with it, though from a slightly different viewpoint, and all students of the past history of the earth will gain from it a wider knowledge of their specialty. To all observers of life, to all philosophers, the whole history of plants, which only approaches completion when the fossils are studied, and compared or contrasted with living forms, affords a wonderful illustration of the laws of evolution on which are based most of the modern conceptions of life. Even to those whose profession necessitates purely practical lines of thought, fossil botany has something to teach; the study of coal, for instance, comes within its boundaries. While to all who think on the world at all, 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 volume. © ANCIENT PLANTS CHAPTER II VARIOUS KINDS OF FOSSIL PLANTS Of the rocks which form the solid earth of to-day, a very large proportion have been built up from the deposits at the bottom of ancient oceans and lakes. The earth is very old, and in the course of its history STRUCTURE. OF FOSSIL .PLANTS 69 number of palzozoic fructifications must be considered in the next chapter. CPAPITER Vi MINUTE STRUCTURE OF FOSSIL PLANTS—DIFFER- ENCES FROM LIVING ONES We have seen in the last chapter that the main morphological divisions, roots, stems, leaves, and fructifi- cations, were as distinct in the Coal Measure period as they are now. There is one structure, however, found in the Coal Measure fossils, which is hardly paralleled by anything similar in the living plants, and that is the fossil known as Stgmaria. Stigimaria is the name given, not to a distinct species of plant, but to the large rootlike organs which we know to have belonged to all the species of Lepzdodendron and of Szgzllaria. In the frontispiece these organs are well seen, and branch away at the foot of the trunk, spreading horizontally, to all appearance merely large roots. They are. especially regularly developed, however, the main trunk giving rise always to four primary branches, these each dividing into two equal branches, and so on—in this they are unlike the usual roots of trees. They bore numerous rootlets, of which we know the structure very well, as they are the commonest of all fossils, but in their in- ternal anatomy the main ‘‘roots” had not the structure which is characteristic of roots, but were like s¢ems. In living plants there are many examples of stems which run underground, but they always have at least the. rudiments of leaves in the form of scales, while the fossil structures have apparently no trace of even the smallest scales, but bear only rootlets, thus resembling true roots. _The questions of morphology these struc- tures raise are too complex to be discussed here, and 70 ANCIENT PLANTS Stigmaria is only introduced as an example, one of the very few available, of a palzeozoic structure which seems to be of a nature not clearly determinable as either root, stem, leaf, or fructification. Among living plants the fine rootlike rhizophores of Selaginella bear some resemblance to: Stigmaria in essentials, though so widely different from them in many ways, and they are probably the closest. analogy to be found among the plants of to-day. The individual cells, we have already seen, are strikingly similar in the case of fossil and living plants. There are, of. course, specific varieties peculiar to the fossils, of which perhaps the most striking seem to be some forms of 4az7 cells. For example, in a species of fern from the French rocks there. were mul- ticellular hairs which looked like little stems of Equisetum owing : aoe to regular bands of teeth at the Mi eagerness 1 igh ee junctions of the cells. These hairs ring of secondary wood s were quite characteristic of the species—but. hairs of all sorts have always abounded in variety, so that such distinction has but minor significance. As was noted in the-table (p. 58) the only cell types of prime importance which were not evolved by the Paleozoic plants were the wood vessels, phloem and accompanying cells which are characteristic. of the flowering plants. Among the fossils the vascular arrangements are most interesting, and, as well as all the types of stele development noted in the previous chapter as common to both living and fossil plants, there are further varieties found only among the fossils (see fig. 50). The simple protostele described (on p. 61) is still found, particularly in the very young stages of living STRUCTURE OF FOSSIL PLANTS 71 ferns, but it is a type of vascular arrangement which is not common in the mature plants of the present day. _In the Coal Measure period, however, the protostele was characteristic of one of the two main groups of ferns. In different species of these ferns, the protostele assumed a large variety of shapes and forms as well as the simple Fig. 49.—Lepzdodendron, showing Part of the Hollow Ring of Primary Wood w, with a relatively large amount of Secondary Tissue s, surrounding it cylindrical type. The central mass of wood became five- rayed in some, star-shaped, and even very deeply lobed, with slightly irregular arms, but in all these cases it re- mained fundamentally monostelic. Frequently secondary tissue developed round the protosteles of plants whose living relatives have no such tissue. A case of this kind is illustrated in fig. 48, which shows a simple circular stele surrounded by a zone of secondary woody tissue in a species of Lepzdodendron. | : In many species of Lepzdodendron the quantity of 72 ANCIENT PLANTS secondary wood formed round the primary stele was very great, so that (as is the case in higher plants) the primary wood became relatively insignificant compared with it. In most species of Lepzdodendron the primary stele is a hollow ring of wood (cf. fig. 38, p. 62) round which the secondary wood developed, as is seen in fig. 49. These two cases illustrate a peculiarity of fossil plants. Among living ones the solid and the simple ring stele are almost confined to the Pteridophytes, where second- ary wood does not develop, but the palzozoic Pterido- phytes, while having the simple primary types of steles, had quantities of secondary tissue, which was cor- related with their large size and dominant posi- tion. Among = polystelic Fig. 50.—Diagram of Steles of the English types (see Pp: 63) we Medullosa, showing three irregular, solid, steles find interesting exam- A, with secondary thickenings Ss, all round each. | bi f Al a, Small accessory steles pies in the fossi group of the Medullosee, which are much more complex than any known at present, both owing to their primary structure and also to the peculiar fact that all the steles developed second- ary tissue towards the inner as well as the outer side. One of the simpler members of this family found in the English Coal. Measures is illustrated in fig. 50. Here there are three principal protosteles (and several irregular minor ones) each of which has a considerable quantity of secondary tissue all round it, so that a portion of the se- condary wood is growing in towards the actual centre of the stem as a whole—a very anomalous state of affairs. In the more complex Continental type of J/edullosa there are very large numbers of steles. In the one figured from the Continent in fig. 51 but a few are re- presented. There is a large outer double-ring stele, with STRUCTURE OF FOSSIL PLANTS 73 secondary wood on both sides of it, and within these a number of small steles, all scattered through the ground tissue, and each surrounded by secondary wood. In actual specimens the number of these central steles is much greater than that indicated in the diagram. No plant exists to-day which has such an arrangement ) of its vascular cylinder. It almost appears as though at’ the early period, when the Medullosez flourished, steles were experimenting in various directions. Such types as are illustrated in figs. 50 and 51 are obviously waste- ful (for secondary wood de- veloping towards the centre of a stem is bound to finally meet), and complex, but apparently inefficient, which may partly account for the fact that this type of struc- ture has not survived to the present, though simpler and Fig. 51.—Continental Jedu/losa, show- equally ancient types have ing R, outer double-ring stele with second- done Ye) ary wood all round it; Ss, inner stellate 2 steles, also surrounded in each case by Further details of the secondary tissue ' anatomy of fossils will be mentioned when we come to consider the individual families; those now illustrated suffice to show that in the Coal Measures very different arrangements of steles were to be found, as well as those which were similar to those existing now. The significance of these differ- ences will become apparent when their relation to the other characters of the plants is considered. The fructifications, always the most important parts of the plant, offer a wide field, and the divergence be- tween the commoner palzozoic and recent types seems at first to be very great. Indeed, when palzozoic repro- ductive bodies have to be described, it is often necessary to use the common descriptive terms in an altered and wider sense. (0122) 7 74 ANCIENT PLANTS Among the plants of to-day there are many varieties of the simple single-celled reproductive masses which are called spores, and which are usually formed in large numbers inside a spore case or sporangium. Among the higher plants seeds are also known in endless variety, all of which, compared with spores, are very complex, for they are many-celled structures, consisting essentially of an embryo or young plant enclosed in various protec- tive coats. The distinction between the two is sharp and well defined, and for the student of living plants there exists no difficulty in separating and describing seeds and spores. But when we look back through the past eras to palzeozoic plants the subject is not so easy, and the two main types of potentially reproductive masses are not sharply distinct. The seed, as we know it among recent plants, and as it is generally defined, had not fully evolved; while the spores were of great variety and had evolved in several directions, some. of which seem to have been intermediate stages between simple spores and true seeds. These seedlike spores served to reproduce the plants of the period, but their type has since died out and left but two main methods among living plants, namely the essentially simple spores, the very simplicity of whose organization gives them a secure position, and the complex seeds with their infinite variety of methods for protecting and scale the young em- bryos they contain. Among the Coal Measure fossils we can pick up some of the early stages in the evolution of the seed from the spore, or at least we can examine intermediate stages between them which give some idea of the possible course of events. Hence, though the differences from our modern reproductive structures are so noticeable a feature of the palzeozoic ones, it will be seen that they are really such differences as exist between the members at the two ends of a series, not such as exist between unrelated objects. STRUCTURE OF FOSSIL PLANTS 75 Very few types can be mentioned here, and to make their relations clear a short series of diagrams with explanations will be found more helpful than a detailed account of the structures. Fig. 52.—Spores Each spore a single cell which develops with three others in tetrads (groups of four). Very numerous tetrads enclosed in a spore ‘case or sporangium which develops on a leaf- like segment called the sporophyll. Each spore germinates independently of the others after being scattered, all being of the same size. Common in fossils and living Pterido- phytes, Fig. 53.—Spores Each a single cell like the preceding, but here only one tetrad in a sporangium ripens, so that each contains only four spores. Compared with the preceding types these spores are very large. Otherwise details similar to above. Some fossils have such sporangia with eight spores, or some other small number; living Selaginellas have four. In the same cone sporangia with small spores are developed and give rise to the male organs. Fig. 54.—‘‘ Spores’’ of Seedlike Structure Out of a tetrad in each sporangium only one spore ripens, S in figure, the others, s, abort. The wall of the sporangium, w, is more massive than in the pre- ceding cases, and from the sporophyll, flaps, spf, grow up on each side and enclose and protect the sporangium. ‘The one big spore appears to germi- nate inside these protective coats, and not to be scat- tered separately from them. Only found in fossils, ‘one of the methods of reproduction in Lepidodendron. Other sporangia with small spores were developed which gave rise to the male organs. 76 ANCIENT PLANTS Fig. 55.—‘‘ Seed” In appearance this is like a seed, but differs from a true seed in having no embryo, and is like the preceding structure in having a very large spore, s, though there is no trace of the three aborting ones. The spore develops in a special mass of tissue known as the nucellus, ~, which partly corresponds to the sporangium wall of the previous types. In it a cavity, pc, the pollen chamber, receives the pollen grains which enter at the apex of the ‘‘seed”. There is a complex coat, C, which stands round the nucellus but is not joined to it, leaving the space 7 between them. Only in fossils; Tvrigonocarpus (see p. 122) is similarly organized. Small spores in fern-like sporangia, called pollen grains. { . Fig. 56.—'* Seed” Very similarly organized to the above, but the coat is joined to the nucellus about two- thirds of its extent, and up to the level 7. In the pollen chamber, gc, a cone of nucellar tissue projects, and the upper part of the coat is fluted, but these complexities are not of primary importance.. The large spore s ger- minated and was fertilized within the ‘‘seed”’, but apparently produced no embryo before it ripened. Small ‘‘spores” in fern-like spo- rangia form the pollen grains. Only in fossils, e.g. Lagenostoma. (See p. 119.) Fig. 57.—Seed Essentially similar to the preceding, except in the possession of an embryo e, which is, however, small in comparison with the endosperm which fills the spore s. The whole organization is simpler than in the fossil Lagexostoma, but the coat is. fused to the nucellus further up (see 2). Small ‘‘ spores’’ form the pollen grains. Living and fossil type, Cycads and Ginkgo. a eet ye ee STRUCTURE OF FOSSIL PLANTS ay Fig. 58.—Seed In the ripe seed the large embryo e practically fills up all the space within the two seed coats c! and c?; endosperm, pollen chamber, &c., have been elimi- nated, 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 enclosed. Small ‘‘spores” form the pollen grains. Typical of living Dicoty- ledons. These few illustrations represent only the main divi- sions of an army of structures with an almost unima- ginable wealth of variety which must be left out of consideration. For the structures illustrated in figs. 54, 55, and 56 we have no name, for their possible existence was not conceived of when our terminology was invented, and no one has yet christened them anew with distinct names. They are evidently too complex in organiza- tion and too similar to seeds in several ways to be called spores, yet they lack the essential element in a seed, namely, an embryo. The term ‘‘ovule” (usually given to the young seed which has not yet developed an embryo) does not fit them any better, for their tissues are ripened and hard, and they were of large size and apparently fully grown and mature. or the present a name is not essential; the one thing that is important is to recognize their intermediate character and the light they throw on the possible evolu- tion of modern seeds. A further point of great interest is the manner in which these ‘“‘seeds” were borne on the plant. To-day seeds are always developed (with the exception of Cycas) in cones or flowers, or at least special inflorescences. But the “seed” of Lagenostoma (fig. 56), as well as a number of others in the group it represents, were not borne on a special structure, but directly on the green 78 ANCIENT PLANTS foliage leaves. They were in this on a level with the simple sporangia of ferns which appear on the backs of the fronds, a fact which is of great significance both for our views on the evolution of seeds as such, and for the bearing it has on the relationships of the various groups of allied plants. This will be referred to subsequently (Chapter XI), and is mentioned now only as an example of the difference between some of the characters of early fossils and those of the present day. It is true that botanists have long recognized the organ which bears seeds as a modified leaf. The carpels of all the higher plants are looked on as homologous with leaves, although they do not appear to be like them externally. Sometimes among living plants curious diseases cause the carpels to become foliar, and when | this happens the diseased carpel reverts more or less to the supposed ancestral leaf-like condition. It is only among the ancient (but recently discovered) fossils, how- ever, that: seeds are known to be borne normally on foliage leaves. From Mesozoic plants we shall learn new conceptions about flowers and reproductive inflorescences in general, but these must be deferred to the consideration of the family as a whole (Chapter XIII). Enough has been illustrated to show that though the individual cells, the bricks, so to speak, of plant construction, were so similar in the past and present, yet the organs built up by them have been continually varying, as a child builds increasingly ambitious palaces with the same set of bricks. PAST HISTORIES OF PLANT FAMILIES 79 CHAPTER VIII PAST HISTORIES OF PLANT FAMILIES I. Flowering Plants, Angiosperms In comparison with the other groups of plants the flowering families are of recent origin, yet in the sense in which the word is usually used they are ancient indeed, and the earliest records of them must date at least to periods hundreds of thousands of years ago. Through all the Tertiary period (see p. 34) there were numerous flowering plants, and there is evidence that many families of both Monocotyledons and Dicoty- ledons existed in the Upper Cretaceous times. Further back than this we have little reliable testimony, for the few specimens of so-called flowering plants from the Lower Mesozoic are for the most part of a doubtful nature. The flowering plants seem to stand much isolated from the rest of the plant world; there is no dvect evi- dence of connection between their oldest representatives and any of the more primitive families. So far as our actual knowledge goes, they might have sprung into being at the middle of the Mesozoic period quite inde- pendently of the other plants then living; though there are not wanting elaborate and almost convincing theories of their connection with more than one group of their predecessors (see p. 108). 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 Measures, they have pre- served for us far less well the plants which were living when they were formed. Hitherto no one has found in Mesozoic strata masses of exquisitely mineralized Angio- sperm fragments? like those found in the Coal Measures, 1 Material recently obtained by the author and Dr. Fujii in Japan does contain some true petrifactions of Angiosperms and other plant debris. The account of these discoveries has not yet been published. 80 ANCIENT PLANTS which tell us so much about the more ancient plants. Cases are known of more or less isolated fragments with their microscopical tissues mineralized. For example, — there are some palms and ferns from South America — which show their anatomical structure very clearly pre- served in silica, and which seem to resemble closely the living species of their genera. The bulk of the plants preserved from these periods are found in the form of casts or impressions (see p. 10), which, as has been pointed out already, are much less satisfactory to deal with, and give much less reliable results than specimens which have also their internal structure petrified. The quantity of material, however, is great, and impressions of single leaves innumerable, and of specimens of leaves attached to stems, and even of flowers and fruits, are to be found in the later beds of rock. These are generally clearly recognizable as belonging to one or other of the living families of flowering plants. Leaf impres- sions are by far the most frequent, and our knowledge of the Tertiary flora is principally derived from a study of them. Their outline and their veins are generally preserved, often also their petioles and some indication of the thickness and character of the fleshy part of the leaf. From the outline and veins alone an expert is generally able to determine the species to which the plant belongs, though it is not always quite safe to trust to these determinations or to draw wide-reaching conclusions from them. In fig. 59 is shown a photograph of the impression of a Tertiary leaf, which illustrates the condition of an average good specimen from rocks of the period. Its shape and the character of the veins are sufficient to mark it out immediately as belonging to the Dicotyle- donous group of the flowering plants. Seeds and fruits are also to be found; and in some very finely preserved specimens from Japan stamens from a flower and delicate seeds are seen clearly im- pressed on the light stone. In fig. 60 is illustrated a PAST HISTORIES OF PLANT FAMILIES 81 Fig. 59.—Dicotyledonous Leaf Impression from Tertiary Rocks couple of such seeds, which show not only their wings but also the small antennz - like stigmas. Specimens so _ perfectly preserved are practically as good as herbarium material of recent plants, and in this way the ex- ternals of the Tertiary plants are pretty well known to us. A problem which has long been discussed, and which has aroused much interest, is the relative an- : ° ° Fig. 60.—Seeds from Japanese tiquity of the Monocotyledonous Tertiary Rocks; at @ are seen and the Dicotyledonous branches _ the two stigmas still preserved of the flowering plants. A peculiar fascination seems to hang over this still unsolved riddle, and a battle of flowers may be said to rage between the (c 122) 8 82 ANCIENT PLANTS lily and the rose for priority. Recent work has thrown no decisive light on the question, but it has undoubtedly demolished the old view which supposed that the Mono- cotyledons (the lily group) appeared at a far earlier date upon this earth than the Dicotyledons. The old writers based their contention on incorrectly determined fossils. For instance, seeds from the Palzeozoic rocks were de- scribed as Monocotyledons because of the three or six ribs which were so characteristic of their shell; we know now that these seeds (7rzgonocarpus) belong to a family already mentioned in another connection ‘(p. 72), the Medullosezee (see p. 122), the affinity of which lies between the cycads and the ferns. Leaves of Cordaztes, again, which are broad and long with well-marked parallel veins, were described as those of a Mono- cotyledonous plant like the Yucca of to-day; but we now know them to belong to a family of true Gymno- sperms possibly distantly related to Zaxus (the Yew tree). Recent work, which has carefully sifted the fossil evidence, can only say that no true Monocotyledons have yet been found below the Lower Cretaceous rocks, and that at that period we see also the sudden inrush of Dicotyledons. Hence, so far as paleontology can show, the two parallel groups of the flowering plants arose about the same time. It is of interest to note, however, 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 Liliacez. In the same nodules, however, there are several specimens of Dicotyledonous woods, so that it does not throw any light on the question of priority. With the evidence derived from the comparative study of the anatomy of recent flowering plants we cannot concern ourselves here, beyond noting that the results weigh in favour of the Dicotyledons. as being the more primitive, though not necessarily developed much earlier in point of time. Until very much more is discovered than is yet known of the origin of the PAST HISTORIES OF PLANT FAMILIES 83 flowering plants as a whole, it is impossible to come to a more definite conclusion about this much-discussed subject. Let us now attempt to picture the vegetable com- munities since the appearance of the flowering plants. The facts which form the bases of the following concep- tions have been gathered from many lands by numerous workers in the field of fossil botany, from scattered plant remains such as have been described. When the flowering plants were heralded in they appeared in large numbers, and already by the Creta- ceous period there were very many different species. Of these a number seem to belong to genera which are still living, and many of them are extremely like living species. It would be wearisome and of little value to give a list of all the recorded species from this period, but a few of the commoner ones may be mentioned to illustrate the nature of the plants then flourishing. Several species of Quercus (the Oak) appeared early, particularly Quercus Llex; leaves of the /uglandacee (Walnut family) were very common, and among the Tertiary fossils appear its fruits. Both Populus (the Poplar) and Safx (the Willow) date from the early rocks, while /zcus (the Fig) was very common, and Casuarina (the Switch Plant) seems to have been widely spread. Magnolias also were common, and it appears that Platanus (the Plane) and Eucalyptus coexisted with them. It will be immediately recognized that the above plants have all living representatives, either wild or cultivated, growing in this country at the present day, so that they are more or less familiar objects, and there appears to have been no striking difference between the early flowering plants and those of the present day. Be- tween the ancient Lycopods, for example, and those now living the differences are very noteworthy; but the earliest of the known flowering plants seem to have been essen- tially like those now flourishing. It must be remem- — 84 3 ANCIENT PLANTS. bered in this connection that the existing flowering plants are immensely nearer in point of time to their origin than are the existing Lycopods, and that when ~such zons have passed as divide the present from the Paleozoic, the flowering plants of the future may have dwindled to a subordinate position corresponding to that held by the Lycopods now. A noticeable character of the early flowering-plant flora, when taken as a whole, is the relatively large proportion of plants in it which belong to the family Amentifere (oaks, willows, poplars, &c.). This is sup- posed by some to indicate that the family is one of the most primitive stocks of the Angiosperms. This view, however, hardly bears very close scrutiny, because it derives its main support from the large numbers of the Amentiferee as compared with other groups. Now, the Amentiferze were (and are) largely woody resistant plants, whose very nature would render them more liable to be preserved as impressions than delicate trees or herbs, which would more readily decay and leave no trace. Similarly based on uncertain evidence is the surmise that the group of flowers classed as Gamopetale (flowers with petals joined up in a tube, like convolvulus) did not flourish in early times, but are the higher and later development of the flower type. Now, Vzburnum (allied to the honeysuckle) belongs to this group, and it is found right down in the Cretaceous, and Saméucus (Elder, of the same family) is known in the early Ter- tiary. These two plants are woody shrubs or small trees, while many others of the family are herbs, and it is. noteworthy that it is just these woody, resistant forms which are preserved as fossils; their presence demon- strates the antiquity of the group as a whole, and the absence of other members of it may be reasonably attri- buted to accidents of preservation. In the Tertiary also we get a member of the heath family, viz. Andromeda, and another tube-flower, Bzgnonza, as well as several more woody gamopetalous flowers. PAST HISTORIES OF PLANT FAMILIES 85 Hence it is wise to be very cautious about drawing any important conclusions from the relative numbers of the different species, or the absence of any type of plant from the lists of those as yet known from the Cretaceous. When quantities of structurally preserved material can be examined containing the flowering plants in petrifac- tions, then it will be possible to speak with some security of the nature of the Mesozoic flora as a whole. The positive evidence which is already accumulated, however, is of great value, and from it certain deductions may be safely made. 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 globe. In America and in Central Europe, for example, the same types of plants were growing. We shall see that, as time advanced, the vari- ous types became separated out, dying away in different | places, until each great continent and division of land | had a special set of plants of its own. At the com-| mencement of the reign of flowering plants, however, they seem to have lived together in the way we are told the beasts first lived in the garden of Eden. At the beginning of the Tertiary period: there were still many tropical forms, such as Palms, .Cycads, Vzfa, various Artocarpacee, Lauracee, A iy S383) and others, growing side by side with such temperate forms as Quercus, Alnus, Betula, Populus, Viburnum, and others of the same kind. Before the middle of the Tertiary was reached the last Cycads died in what is now known as Europe; and soon after the middle Tertiary all the tropical types died out of this zone. “At the same time those plants whose leaves appear to have fallen at the end of the warm season began to become common, which is taken as an indication of a climatic influence at work. Some writers consider that in the Cretaceous times there was no cold season, and) therefore no regular period of leaf fall, but as the climate became temperate the deciduous trees increased 86 ANCIENT PLANTS in numbers; yet the Gymnospermic and Angiospermic woods which are found with petrified structure show well-marked annual rings and seem to contradict this view. Toward the end of the Tertiary times there were practically no more tropical forms in the European flora, though there still remained a number of plants which are now found either only in America or only in Asia. The Glacial epoch at the close of the Tertiary appears to have driven all the plants before it, and afterwards, when its glaciers retreated, shrinking up to the North and up the sides of the high mountains, the plant species that returned to take possession of the land in the Quaternary or present period were those which are still inhabiting it, and the floras of the tropics, Asia, and America were no longer mixed with that of Europe.? CHAPTER IX PAST HISTORIES OF PLANT FAMILIES II. Higher Gymnosperms The more recent history of the higher Gymnosperms, in the Upper Cretaceous and Tertiary periods, much resembles that of the flowering plants as sketched in the previous chapter. Many of the genera appear to have _been those still living, and some of the species even may ‘have come very close to or have been identical with | those of to-day. The forms now characteristic of the _ different continents were growing together, and appear to have been widely distributed over the globe. For example, Seguoza and Taxodium, two types now charac- teristic of America, and Glyptostrobus, at present found 1A fuller account of the Angiospermic flora can be had in F rench, in M. Laurent’s paper in Progressus Ret Botanice. See Appendix for reference. PAST HISTORIES OF PLANT FAMILIES 87 in Asia, were still growing with the other European types in Europe so late as middle Tertiary times. As in the case of the Angiosperms, the fossils we have of Cretaceous and Tertiary Gymnosperms are nearly all impressions and casts, though some more or less iso- lated stems have their structure preserved. Hence our knowledge of these later Gymnosperms is far from com- plete. From the older rocks, however, we have both impressions and microscopically preserved material, and are more fully acquainted with them than with those which lived nearer our own time. Hard, resistant leaves, which are so characteristic of most of the living genera of Gymnosperms, seem to have been also developed in| the past members of the group, and these tend to leave clear impressions in the rocks, so that we have reliable data for reconstructing the external appearance of the fossil forms from the Palzeozoic period. The resinous character of Gymnosperm wood prob- ably greatly assisted its preservation, and fragments of it are very common in rocks of all ages, generally pre- served in silica so as to show microscopic structure. The isolated wood of Gymnosperms, however, is not very instructive, for from the wood alone (and usually it is just fragments of the secondary wood which are preserved) but little of either physiological or evolutional value can be learned. When twigs with primary tissues and bark and leaves attached are preserved, then the specimens are of importance, for their true character can be recognized. Fortunately among the coal balls there are many such fragments, some of which are accompanied by fruits and male cones, so that we know much of the Paleozoic Gymnosperms, and find that in some respects they differ widely from those now living. There is, therefore, much more to be said about the fossil Gymnosperms than about the Angiosperms, 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 record. Indeed, we 88 i ANCIENT PLANTS do not know when the Gymnosperms began; the well- developed and ancient group of Cordaztee was flourish- ing before the Carboniferous period, and must therefore date back to the rocks of which we have no reliable information from this point of view, and the origin of the Gymnosperms must lie in the pre-Carboniferous period. The group of Gymnosperms includes a number of genera of different types, most of which may be arranged under seven principal families. In a sketch of this nature it is, of course, quite impossible to deal with all the less- important families and genera. Those that will be considered here are the following :— ( Genera both living and fossil. pia Miahit | Fossil forms undoubted so raucaree, ¢.g. Monkey-puzzle far back as the Jurassic, and presumably further. Genera both living and fossil, Coniferales | 4detineez, e.g. Pine and Larch ; Fossils recognized as far back (see p. 90). 4 as the Lower Cretaceous. ; ; : Genera both living and fossil. Cupresse@, ¢.g. Juniper, Cypress} Fossils recognized as far back as the Jurassic. Genera living and fossil. Taxee, e.g. Yew Fossils recognized as far back L as the Cretaceous. ( f Fossil only. , ~ Characteristic of Devonian, Cendalteins Cordaitee, eg. Cordaites | Cabbenifcrous,’ and? Pos : mian periods. (see p. 92). Fassih Gale. | Characteristic of the Carboni- ferous and Permian. | ie and living, dating Poroxylee@, ¢.g. Poroxylon \ Ginkgoales (see p 98) back, apparently with little | Ginkgoacee, e.g. Ginkgo change, to Palzeozoic times. We must pay the most attention to the two last groups, as they are so important as fossils, and the Cordaitee were a very numerous family in Coal Measure times. They had their period of principal development so long ago that it is probable that no direct descendants remain to the present time, though some botanists con- sider that the Zaze are allied to them. Of the groups still living it is difficult, almost impos- PAST HISTORIES OF PLANT FAMILIES 89 sible, to say which is the highest, the most evolved type. In the consideration of the Gymnosperm family it is brought home with great emphasis how incomplete and partial our knowledge is as yet. Many hold that the Araucareeé are the most primitive of the higher Gymno- sperms. In support of this view the following facts are noted. They have a simple type of fructification, with a single seed on a simple scale, and many scales arranged round an axis to form a cone. In the microscopic struc- ture of their wood they have double rows of bordered pits, a kind of wood cell which comes closer to the old fossil types than does the wood of any of the other living genera. Further than this, wood which is almost indis- tinguishable from the wood of recent Araucarias is found very far back in the rocks, while their leaves are broad and simple, and attached directly to the stem in a way similar to the leaves of the fossil Cordaztee, and very different from the needle leaves on the secondary stems of the Pine family; ‘so that there appears good ground for considering the group an ancient and probably a primitive one.’ On the other hand, there are not wanting scientists who consider the Adzetznee the living representatives of the most primitive and ancient stock, though on the whole the evidence seems to indicate more clearly that the Pine-tree group is specialized and highly modified. Their double series of foliage leaves, their complex cones (whose structures are not yet fully understood), and their wood all support the latter view. Some, again, consider the Zaxee as a very primitive ‘group, and would place them near the Cordaitez, with which they may be related. Their fleshy seeds, growin not in cones but on short special axes, support this view, and it is certainly true that in many ways the large seeds, with their succulent coats and big endosperm, are much 1From the Cretaceous deposits of North America several fossil forms (Bvachy- phyllum, Protodammara) are described which show clear affinities with the family as it is now constituted. (See Hollick and Jeffrey; reference in the Appendix.) go ANCIENT PLANTS like those of the lower Gymnosperms and of several fossil. types. Those, however, who hold to the view that the: Abietinez are primitive, see in the 7Zazee the latest and most modified type of Gymnosperm. It will be seen from this that there is no lack of variety regarding the interpretation of Gymnosperm structures. The Gymnosperms do not stand in such an isolated position as do the Angiosperms. Whatever the variety of views held about the details of the relative placing” of the families within the group, all agree in recog- nizing the evidence which enables us to trace with confidence the connection between the lower Gymno- sperms and the families of ferns. There are many indications of the intimate connection between higher and lower Gymnosperms. Between the series exist what might be described as different degrees of cousin- ship, and in the lower groups lie unmistakable clues to: their connection with more ancient groups in the past which bridge over the gaps between ther and the ferns. For the present, however, let us confine ourselves to. the history of the more important Gymnosperms, 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 mentioned. To a consideration of the living families of Avau- caree, Abtetinee, Cupressee, and Taxee we can allow but a short space; their general characters and appear- ance are likely to be known to the reader, and their details..can be studied from living specimens if they are not. For purposes of comparison with the fossils, however, it will be necessary to mention a few of the principal features which are of special importance in. discussing phylogeny. The ARAUCARIACE& are woody trees which attain a considerable size, with broad-based, large leaves attached. directly to the stem. In the leaves are a series of numer- ous parallel vascular bundles. The wood cells in micro- PAST HISTORIES OF PLANT FAMILIES QF scopic section show two rows or more of round bordered pits. The cones are very large, but the male and female are different in size and organization. The female cone is composed of series of simple scales arranged spirally round the axis, and each scale bears a single seed and a small ligule. The pollen grains from the male cone are caught on the ligule and the pollen tubes enter the micropyle of the ovule, bringing in passive male cells which may develop in large numbers in each grain. The seeds when ripe are stony, and some are provided with a wing from part of the tissue of the scale. In the ripe cones the scales separate from the cone axis. The ABIETINE& are woody trees, some reaching a great height, all with a strong main stem. The leaves are of two kinds: primary ones borne directly attached to the stem (as in first-year shoots of the Larch), and secondary ones borne in tufts of two (in Pine) or a large number (in older branches of Larch) on special short branches, the primary leaves only developing as brown scales closely attached to the stems. Leaves generally very fine and needlelike, and with a central vascular bundle. The wood in microscopic section shows a single row of round bordered pits on the narrow trachez. The female cones are large, male and female differing greatly in size and organization. The female cone, com- posed of a spiral series of pairs of scales, which often fuse together as the cone ripens. Each upper scale of the pair bears two seeds. The pollen grains from the male cone enter the micropyle of the seed and are caught in the tissue (apex of nucellus) there; the pollen tubes discharge passive male cells, only two of which develop in each grain. The seeds when ripe are stony and pro- vided with a wing from the tissue of the scale on which they were borne. The CupressE& are woody trees reaching no great height, and of a bushy, branching growth. The leaves are attached directly to the main stem, and arrange Q2 ANCIENT PLANTS themselves in alternating pairs of very small leaves, closely pressed to the stem. The wood in microscopic section shows a single row of round bordered pits on the trachez. The cones are small, and the scales forming them arranged in cycles. The female scales bear a varying number of seeds. The pollen grain has two passive male cells. The seeds when ripe are stony, with wings, though in some cases (species of Juniper) the cone scales close up and become fleshy, so that the whole fruit resembles a berry. The Taxea# are woody, though not great trees, bushily branched. ‘The leaves are attached spirally all round the stem, but place themselves so as to appear to lie in pairs arranged in one horizontal direction. The wood in microscopic section shows a single row of round bordered pits on the trachez. | There are small male cones, but the seeds are not borne on cones, growing instead on special short axes, where there may be several young ovules, but on which usually two seeds ripen. The seeds are big, and have an inner stone and outer fleshy covering. Some have special outer fleshy structures known as “‘arils”, ¢.g. the red outer cup round the yew “berry” (which is not a berry at all, but a single unenclosed seed with a fleshy coat). When we turn to the Corea we come to a group. of plants which bears distinct relationship to the preceding, but which has a number of individual char- acters. It is a group of which we should know nothing were it not for the fossils preserved in the Palzozoic rocks; yet, notwithstanding the fact that it flourished so long ago, it is a family of which we know much. At the time of the Coal Measures and the succeeding Permo-carboniferous period, it was of great importance, and, indeed, in some of the French deposits it would seem as though whole layers of coal were composed entirely of its leaves. PAST HISTORIES OF PLANT FAMILIES 93 Among the fossil remains of this family there are impressions, casts, and true petrifactions, so that we know both its external appearance and the internal anatomy of nearly every part of several species of the genus. For a long time the various fossil re-- mains of the plant were not recognized as belonging to each other and together forming the records of one and the same plant—the broad, long leaves with their parallel veins were looked on as Monocotyledons (see fig. 61); the pith casts (see fig. 63) were thought to be peculiar constricted stems, and were called Sternbersia; while the wood, which was known from its microscopic structure, was called Araucarioxylon— but the careful work of many masters of fossil botany, whose laborious studies we cannot describe in detail here, brought all these fragments together and proved them to belong to Cordaztes. We now know that Cordaztes were large trees, with strong upright shafts of wood, to whose branches large simple leaves were attached. The leaves were much bigger than those of any living Gymnosperm, even than those of the Kauri Pine (a member of the Arau- cariaceze), and seem in some species to have exceeded 3 ft. in length. The trees branched only at the top of the main shaft, and with their huge sword- like leaves must have differed greatly in appearance from any plant now WOo¥ Fig. 61.— Leaf of Cor- daites, 1, attached by its broad base to a Stem, s living. The leaves had many parallel veins, as can be seen in fig. 61, and were attached by a broad base directly to the main stem; thus coming closer to the 94 ANCIENT PLANTS Araucarias than the other groups of Gymnosperms in their leaf characters. The internal anatomy is often well preserved, and ws ae er ee eee. ee Cs. tee ‘ 2 weer » 7 nie, ¢ 6 Be: Oso: Bae eS. yar, Oi b 3 % Paren®? i> a 4 Fig. 62A.—Microscopic Section of Part of a Leaf of Cordaites v, Vascular bundle; w, wood of bundle; sh, its sheath; s!, large sclerenchyma mass alternating with bundles; s*? and s%, sclerenchyma caps of bundle; P, soft tissue of leaf. there is a number of species of leaves whose anatomy is known. As will be expected from the parallel veins, in each section there are many vascular bundles run- ning equidistantly through the tissue. Fig. 624 shows the microscopic details from a well-preserved leaf. In all the species patches of sclerenchyma were developed, and everything indicates that they were tough and well pro- tected against loss of water, even to a Fig. 6aB.—Much-mag- greater extent than are most of the nified Wood Elements leaves of living Gymnosperms. ROE Carre SLE ADEN In the stems the pith was much in longitudinal section, ° ee the type known as draw. larger than that in living Gymnosperms carioxylon. Note the (where the wood is generally very eae ak is solid), and it was hollow in older stems, in several rows except for discs of tissue across the cavity. The internal cast from these stems has been described before, and is seen in fig. 63. The wood was formed in closely packed radiating CUE a0H0 CZ g oO UNTO OTT <3 PAST HISTORIES OF PLANT FAMILIES 95 rows by a normal cambium (see p. 66), and the trachea ‘se formed had characteristic rows of bordered pits (see fig. 628). The wood comes nearer to that of the living Araucarias than any other, and indeed the numerous pieces of fossil wood of this type which are known from all the geological periods are called Araucarioxylon.. A double strand goes out from the main mass of wood, which afterwards divides and subdivides to provide the numerous bundles of the leaf. ” the case of these fossils we are fortunate enough to have the fructifica- tions, both male and female, in a good state of preservation. As in other Gymnosperms, the male and female cones are separate, but they differed less from each other in their arrange- ment than do those of any of the living types hitherto mentioned. They can hardly be described as true cones, though they had something of that nature; the seeds seem to be borne on SS special short stems, round which are _ Fig.63.—Castof Hollow @iegomrmeacales, In the seed and Pith of. Condaties, the > . constrictions correspond- the way it is borne perhaps the Cor- _ jngto discs of solid tissue daiteee may be compared more nearly across the cavity with the Taxeze than with the other groups. A seed, not yet ripe, is shown in slightly dia- grammatic form in fig. 64, where the essential details are illustrated. The seeds of this family sometimes reached a considerable size, and had a fleshy layer which was thick in comparison with the stone, and ex- ternally comparable with a cherry—though, of course, of very different nature in reality, for Cordaztes, like Taxus, is a Gymnosperm, with simple naked seeds, while a cherry is the fruit of an Angiosperm. ' The addition of -oxy/on 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 anformation from the petrified material. 96 ANCIENT PLANTS In a few words, these are the main characters of the large group of Cordaztes, which held the dominant position among Gymnosperms in the Palzozoic era. They have relationships, or perhaps one should say likenesses, to many groups.. Their stem- and _ root- anatomy is similar to the Coniferee of the present day, the position of the ovules is like that in the Taxacee, the male cones in some measure recall those of Ginkgo, the anatomy of their leaves has points which are comparable with those of the Cycads, to which group also the large pith in the stem and the structure of some details in the seeds unite them. Their own specially distinctive characters lie in their crown of huge leaves, and unbranched shaft of stem, the similarity of their ag male and_ female inflores- Fig. 64.—Representation of Cordaztes : AL a Seed and its Axis with Scales, slightly CEMCES, and some points in diagrammatic, modifted from Renault. their pollen grains which A, Axis with s, scales; c, coat of the have not been mentioned. seed, from which the inner parts have “The type isa very complex shrunk away; My nucellus ; pe, pollen one, possibly coming near chamber containing pollen grains which enter through m. the stock which, having branched out in various directions, gave rise to several of the living families. Plants which come very near to the Cordaitez are the PoroxyLe&. Of this group we have unfortunately no remains of fructifications in organic connection, so that its actual position must remain a little doubtful till they are discovered. There seems no doubt that they must have borne seeds. Still, it has been abundantly demonstrated in recent years that the anatomy of the root, stem, and leaves PAST HISTORIES OF PLANT FAMILIES 97 indicates with considerable exactness the position of any plant, so that, as these are known, we can deduce from them, with a feeling of safety, the position that Poroxylon takes in the natural system. In its anatomy the characters are those of the Cordaitez, with certain details which show a more primitive nature and seem to be characteristic of the groups below it in organization. Poroxylon is not common, and until recently had not been found in the Lower Coal Measures of England. The plants appear to have been much smaller than Cordaites, with delicate stems which bore relatively : : large simple leaves. The ms anatomy of the root was 1g that common in Gymno- ¢ sperms, but the stem had a p a very large pith, and the ‘ ¢ leaves were much like those of Cordattes in having Fig. 65.—A, Normal bundie of higher ° * plant; x, protoxylem on inner side next the parallel veins. An im- pith Z, and the older wood w outside it, cez- portant character in the trifugal wood. 8, Bundle with wood cells ¢ developed on inner side of protoxylem, cez- anatomy of the stem was tripetal wood; the arrow indicates the direc- the presence of what is _ tion of the centre of the stem. This must be shortly explained. In all the stems hitherto considered, the first-formed wood cells (protoxylems, see p. 57) developed at the central point of the wood, towards the pith (see fig. 19, Ax, p. 49). This is char- acteristic of all Angiosperms and the higher Gymno- sperms (except in a couple of recently investigated Pines), but among the lower plants we find that part of the later wood develops to the inner side of these pro- toxylem masses. The distinction is shown in fig. 65. This point is one to which botanists have given much attention, and on which they have laid much weight in considering the affinities of the lower Gymnosperms and the intermediate groups between them and the ferns, which are found among the fossils. In Cordaztes this (c 122) 9 98 : ANCIENT PLANTS point of connection with the lower types is not seen, but in Poroxylon, which has otherwise a stem anatomy very similar to Cordaztes, we find groups of centripetal wood developed inside the protoxylem of primary bundles. For this reason, principally, is Poroxydon of interest at present, as in its stem anatomy it seems to connect the Cordartes type with that of the group below it in general organization. GINKGOALES.— Reference to p. 44 shows that Gzzhgo, the Maidenhair tree, belongs to the Ginkgoales, a group taking equal rank with the large and complex series of the Coniferales. The Ginkgoales of the present day, however, have but one living representative. Gznkgo stands alone, the single living species of its genus, repre- senting a family so different from any other living family that it forms a prime group by itself. Had the tree not been held sacred in’ China and Japan, it is probable that it would long since have been extinct, for it is now known only in cultivation. It is indeed a relic from the past which has been fortunately preserved alive for our examination. It belongs to the fossil world, as a belated November rose belongs to the summer. Because of its beauty and interest the plant is now widely distributed under cultivation, and is available for study almost as freely as the other types of living Gymnosperms already mentioned, so that but a short summary of its more important features is needed here. Old plants, such as can be seen growing freely in Japan (in Kew Gardens there is also a fine specimen), are very tall handsome woody trees, with noble shafts and many branches. The leaves grow on little side shoots and are the most characteristic external feature of the tree; their living form is illustrated in fig. 66, which shows the typical simple shape as well as the lobed form — of the leaf which are to be found, with all intermediate stages, on the same tree. No other plant (save a PAST HISTORIES OF PLANT FAMILIES 99 few ferns, which can generally be distinguished from it without difficulty) has leaves at all like these, so that it Fig. 66.—A, Tuft of Gixkgo Leaves, showing their ‘‘maidenhair''-like shape. 8, Single deeply-divided Leaf to be found on the same tree, usually on young branches. is particularly easy to identify the fossil remains, of which there are many. The wood is compact and fine grained, the rings of secondary tissue being developed from a normal cam- bium as in the case of the higher Gymnosperms, and the individual trachezee have round bordered pits. There are small male cones, but the seeds are not borne in cones. They develop on special stalks on which are no scales, but a small mass of tissue at the Fig. 67.—Ripe Stage of Ginkgo base of the seed called the Seeds attached to their Stalk. Zi “collar”. Usually there are two «Coltar” of seed. young ovules, of which often only one ripens to a fleshy seed, though both may mature. The ripe seed reaches the size shown in the diagram, and is orange coloured and very fleshy; within it is a 100 ANCIENT PLANTS stone encasing the endosperm, which is large, green, and starchy, and contains the embryo with two cotyledons. This embryo is small compared with the endosperm, cf. fig. 57, p. 76, which is somewhat similar to that of Ginkgo in this stage. Of the microscopic characters of the reproductive organs the most remarkable is the male cell. This is not a passive nucleus, as in the plants hitherto con- sidered, but is an actzvely swimming cell of some size, provided with a spiral of cilia Pe (hairlike structures) whose movements propel it through the water. In the cavity of the unripe seed these swim towards the female cell, and actively penetrate it. The arrangements of the seed are diagrammatically shown in fig. 68, which should be com- pared with that of Cycas, fig. Fig. 68.—Section through Seed of 76, with which it has many ee points in common. p.c, Pollen chamber in the nucellus 7, The nature of the male which is fused to the coat ¢ to the level . ; ° Z; sc, stony layer in coat; Ss, the big cell in Cordaztes is not yet spore, filled with endosperm tissue (in known, but there is reason one of which will produve the embryo tO Suspect it may have been after fertilization. actively swimming also. As this is uncertain, however, we may consider Gzz&go the most highly organized plant which has such a primitive feature, a feature which is a bond of union between it and the ferns, and which, when it was discovered about a dozen years ago, caused a considerable sensation in the botanical world. To turn now to the fossil records of this family. Leaf impressions of Gzzkgo are found in rocks of nearly all ages back even to the Upper Paleozoic. They show a considerable variety of form, and it is certain that they do not all belong to the same sfeczes as the living plant, PAST HISTORIES OF PLANT FAMILIES IOI but probably they are closely allied. Fig. 69 shows a typical impression from the Lower Mesozoic rocks. In this specimen, the cells of the epidermis were fortunately sufficiently well preserved to be seen with the microscope, and there is a distinct difference in the size and shape of the cells of living and fossil species, see fig. 70; but this difference is slight as com- pared with the great similarity of form and appearance, as can be seen on comparing figs. 69 and 66, B, so that the fossil is at the most a dif- ferent species of the genus Gzzkgo. Among the fossil leaves there is greater variety than among the living ones, and some which are very deeply lobed so as to form a divided Fig. 69.—Leaf Impression of Ginkgo from Mesozoic Rocks of Scotland palm-like leaf go by different names, e.g. Bazera, but they are supposed to belong to the same family. Fossil seeds and male cones are also known as impressions, and are found far back in the Mesozoic rocks. From the fossil impressions it is certain that Gzxkgo and plants closely allied to it were very wide- spread in the past, as they are found all over Europe as well as the other continents. Par- ticularly in the Lower Meso- ZOIC rocks Ginkgo seems to Fig. 7c.—Showing Epidermis with have been a world-wide type Stomates from the lower side of the growing in great abundance. In the Paleozoic the records are not so undoubted, veins. but there is strong evidence Leaf seen in fig. 69 e, Epidermis cells; s, stomates; v, long cells of epidermis lying over the which leads us to suppose that if the genus now living were not then extant, at least other closely related genera were, and there seems to be good grounds for 102 hoe ANCIENT PLANTS \. supposing that Ginkgo and Cordaites may have both arisen from some ancient common stock. CHAPTER X PAST HISTORIES OF PLANT FAMILIES III. The Bennettitales This fascinating family is known only from the fossils, and is so remote in its organization from any common living forms that it may perhaps be a little diffi- cult for those who do not know the Cycads to appre- ciate the position of Bennettites. It would probably be better for one studying fossil plants for the first time to read the chapters on the Cycads, Pteridosperms, and Ferns before this chapter on the present group, which has characters connecting it with that series. Until recently the bulk of the fossils which are found as impressions of stems and foliage of this family were very naturally classed as Cycads. They are extremely common in the Mesozoic rocks (the so-called Age of Cycads), and in the external appearance of both stems and leaves they are practically identical with the Cycads. A few incomplete fructifications of some species have been known in Europe for many years, but it is only recently that they have been fully known. This is owing to Wieland’s? work on the American species, which has made known the complete organization of the fructifi- cations from a mass of rich and well-petrified material. In the Lower Cretaceous and Upper Jurassic rocks of America these plants abound, with their microscopic structure well preserved, and their fructifications show an organization of a different nature from that of any past or present Cycad. 1See reference in the Appendix to this richly illustrated volume. PAST HISTORIES OF PLANT FAMILIES 103 Probably owing to their external appearance, Wieland describes the plants as “Cycads” in the title of his big book on them; but the generic name he uses, Cycade- ozdea, seems less known in this country than the equally well-established name of Bennettetes, which has long been used to denote the European specimens of this family, and which will be used in the following short account of the group. At the present time no family of fossils is exciting more interest. Their completely Cycadean appearance and their unique type of fructification have led many botanists to see in them the forerunners of the Angio- sperms, to look on them as the key to that mystery— the origin of the flowering plants. This position will be discussed and the many facts in its favour noted, but we must not forget that the Bexnettztales have only recently been realized fully by botanists, and that a new toy is ever particularly charming, a new cure particularly effi- cacious, and a new theory all-persuasive. From their detailed study of the flowering plants botanists have leaned toward different groups as the » present representatives of the primitive types. The various claims of the different families to this position cannot be considered here; probably that of the Ranales (the group of families round Ranunculacez as a central type) is the best supported. Yet these plants are most frequently delicate herbs, which would have stood rela- tively less chance of fossilization than the other families which may be considered primitive. They are pecu- liarly remote from the group of Bennettiteze in their vegetative structure, a fact the importance of which seems to have been underrated, for in the same breath we are assured that the Bennettites are a kind of cousin to the ancient Angiosperms, and that the Ranales are among the most primitive living Angiosperms, and there- fore presumably nearest the ancient ones. However, let us leave the charms of controversy on one side and look at the actual structure of the group. 104 ANCIENT PLANTS They were widely spread in Lower Mesozoic times, the plants being preserved as casts, impressions, and with structure in great numbers. The bulk of the described structural specimens have been obtained from the rocks of England, France, Italy, and America, although leaf impressions are almost universally known. The genus Wilhamsonia belongs to this family, and is one of the best known of Mesozoic plant impressions. Externally the Bennettiteze were identical in appearance with stumpy Cycads, and their leaves it is which gave rise to the surmise, so long pre- valent, that the Lower Mesozoic was the “Age of Cycads”, just as it was the Pteridosperm leaves that gave the Paleozoic the credit of being the “Age of Ferns”. In the anatomy of , both stem and leaf, also, the characters | are entirely Cycadean; the outgoing ” leaf trace is indeed simpler in its Fig. 71.—HalfofaLon- course than that of the Cycads. gitudinal Section through : R ° a Rkaiine Coan ol Beanie The fructifications, however, differ lites fundamentally from those of the Cy- ot Sse Pes cads, as indeed they do from those of weeds; sc, sterile scalee @ny known family. They took the between the seeds, form of compact cones, which occurred in very large numbers in the mature plants hidden by the leaf bases. In Wzliamsonia, of which we know much less detail, the fructifications stood away from the main axis on long pedicels. In Lennettztes the cones were composed of series of sheathing scales surrounding a short conical axis on which stood thin radiating stalks, each bearing a seed. Between them were long-stalked sterile scales with ex- panded ends. A part of a cone is illustrated diagram- matically in fig. 71. The whole had much the appear- ance of a complex fruit. In some specimens these features alone are present in the cones, but in younger PAST HISTORIES OF PLANT FAMILIES 105 cones from the American plants further structures are found attached. Below the main axis of the seed-bear- ing part of the cone was a series of large complex leaf- like structures closely resembling fern leaves in their much-divided nature. On the pinne of these leaves were crowded innumerable large sporangia, similar to Fig. 72.—Diagram of Complete Cone of Bennettites A, Central axis of conical shape terminating in the seed-bearing cone s. (After Wieland), and bearing successively Br., bracts, comparable with floral leaves; M, large complex leaves with pollen sacs. those of a fern, which provided the pollen grains. The fossils are particularly well preserved, and have been found with these male (pollen-bearing) organs in the young unopened stages, and also in the mature unfolded condition, as well as the ripening seed cones from which they have faded, just as the stamens fade from a flower when the seeds enlarge. 106 ANCIENT PLANTS “It appears that these huge complex leaflike struc- tures were really stamens, but nevertheless they were rolled up in the circinate form as are young fern leaves, and as they unrolled and spread out round the central cone they must have had the appearance of a whorl of leaves (see fig. 72). This, in a few words, is the main general character of the fructification. The most important features, on which stress is laid, are the following. The association of the male and female structures on the same axis, with the female part adove the male. This arrangement is found only in the flowering plants; the lower plants, which have male and female on the same cone, have them mixed, or the female below, and are in any case much simpler in their entire or- ganization. The conical form of the axis is also important, c, Double-layered seed coat ; ”, crushed : . : nucellus; cof., two cotyledons which as is the fact that it termi- practically fill the seed. nates in the seed-bear ing structures. The position of the individual seeds, each on the end of a single stalk, is remarkable, as are the long-stalked bracts whose shield-like ends join in the protection of the seeds. These structures together give the cone much of the appearance of a complex fruit of a flower- ing plant, but the structure of the seeds themselves is that of a simple’ Gymnosperm. In the seeds, however, was an embryo. In this they differ from all known seeds of an earlier date, which, as has been already noted (see p. 77), are always devoid of one. This embryo is one of the most important features of the plant. It had two cotyledons which filled the seed space (see fig. 73), and left almost no trace of the endosperm. Reference to p. 112 will show that this is an advance on the Cycad seed, which has a small em- Fig. 73.—Diagram of Cross Section of Bennettites Seed, with Embryo PAST HISTORIES OF PLANT FAMILIES 107 bryo embedded in a . large mass of endosperm, and that it practically coincides with the Dicotyledonous type. The seed with its embryo suggested comparison with the Angiosperms long before the complete structure of the fructification was known. The fern-like nature of the pollen-bearing structures is another very important point. Were any one of these leaflike ‘“‘stamens” found isolated its fern-like nature would not have been questioned a year or two ago, and their presence in the “flower” of Bennetiztes is a strong argument in favour of the Fern-Pteridosperm affinities of the group. Had the parts of this remarkable fructification devel- oped on separate trees, or on separate branches or dis- tinct cones of the same one, they would have been much less suggestive than they are at present, and the fructi- fications might well have been included among those of the Gymnosperms, differing little more (apart from the embryo) from the other Gymnosperm genera than they do from each other. In fact, the extremely fern-like nature of the male organs is almost more suggestive of a Pteridosperm affinity, for even the simplest Cycads have well-marked scaly cones as their male organs. The female cone, again, considered as an isolated struc- ture, can be interpreted as being not vitally different from Cordaztes, where the seeds are borne on special short stalks amidst scales. The embryo would, in any case, point to a position among advanced types; but it is so common for one organ of a plant to evolve along lines of its own in- dependently, or in advance of the other organs, that the embryo structure alone could not have been held to counterbalance the Cycadean stems and leaves, the Pteridosperm-like male organs, and the Gymnospermic seeds. But all these parts occur on the same axis, arranged in the manner typical of Angiosperms. The seed- bearing structures at the apex, the “stamens” below them, and 108 ANCIENT PLANTS a series of expanded scales below these again, which it takes little imagination to picture as incipient petals and sepals; and behold—the thing is a flower! And being a “flower”, is in closest connection with the ancestors of the modern flowering plants, which must consequently have evolved from some Cycadean - like ancestor which also gave rise to the Bennettitales. Thus can the flowering plants be linked on to the series that runs through the Cycads directly to the primitive ferns! It is evident that this group, of all those known among the fossils, comes most closely to an approxi- mation of Angiospermic structure and arrangement. Enough has been said to show that in their actual nature they are not Angiosperms, though they have some of their characters, while at the same time they are not Cycads, though they have their appearance. They stand somewhere between the two. Though many botanists at present hold that this mixture of characters indicates a relationship equivalent to a kind of cousin- ship with the Angiosperms, and both groups may be supposed to have originated from a Cycadean stock, this theory has not yet stood the test of time, nor is it sup- ported by other evidence from the fossils. We will go so far as to say that it appears as though some Angio- sperms arose in that way; but flowering plants show so many points utterly differing from the whole Cycadean stock that a little scepticism may not be unwholesome. It is well to remember the Lycopods, where (as we shall see, p. 141) structures very. like seeds were devel- oped at the time when the Lycopods were the dominant plants, and we do not find any evidence to prove that they led on to the main line of seed plants. Similarly, Cycads may have got what practically amounted to flowers at the time when they were the dominant group, and it is very conceivable that they did not lead on to the main line of flowering plants. Whatever view may be held, however, and whatever may be the future discoveries relating to this group of PAST HISTORIES OF PLANT FAMILIES 109: plants, we can see in the Bennettitales points which throw much light on the potentialities of the Cycadean stock, and structures which have given rise to some most interesting speculations on the subject of the Angiosperms. This group is another of the jewels in the crown of fossil botany, 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 plants. CHAPTER XI PAST HISTORIES OF PLANT FAMILIES IV. The Cycads The group of the Cycadales, which has a systematic value equivalent to the Gzzkgoales, contains a much larger variety of genera and species than does the latter. There are still living nine genera, with more than a hundred and fifty species, which form (though a small one compared with most of the prime groups) a well- defined family. They are the most primitive Gymno- sperms, the most primitive seed-bearing plants now living, and in their appearance and characters are very different from.any other modern type. Their external resemblance to the group of the Bennettitales, however, is very striking, and indeed, without the fructifications it would be impossible to distinguish them. The best known of the genera is that of Cycas, of which an illustration is given in fig. 74. The thick, stumpy stem and crown of “palm”-like leaves give it a very different appearance from any other Gymnosperm. Commonly the plants reach only a few feet in height, but very old specimens may grow to the height of 30 ft. or more. The other genera are smaller, and some have short stems and a very fern-like appearance, as, for 110 ANCIENT PLANTS example, the genus S¢taugeria, which was supposed to be a fern when it was first discovered and before fruiting specimens had been seen. The large compound leaves are all borne directly on the main stem, generally in a single rosette at its apex, and as they die off they leave their fleshy leaf bases, which cover the stem and remain for an almost inde- finite number of years. The wood of the main trunks differs from that of the other Gymnosperms in being very loosely built, with a large pith and much soft tissue between the radiating bands of wood. There is a cambium which adds zones of secondary tissue, but it does vase not do its work = See regularly, and the cross section of an Fig. 74.—Plant of Cycas, showing the main stem with the crown of leaves and the irregular branches which old Cycad stem come on an old plant shows. disconnected rings of wood, ac- companied by much soft tissue. The cells of the wood have bordered pits on their walls, and in the main axis the wood is usually all developed in a centrifugal direc- tion, but in the axis of the cones some centripetal wood is found (refer to ¢, fig. 65, p. 97). In their fructifications the Cycads stand even further apart from the rest of the Gymnosperms. One striking point is the enormous size of their male cones. The male cones consist of a stout axis, round which are spiral series of closely packed simple scales covered with pollen- PAST HISTORIES OF PLANT FAMILIES Il bearing sacs (which bear no inconsiderable likeness to fern sporangia), the whole cone reaching 14 ft. in length in some genera, and weighing several pounds. All the other Gymnosperms, except the Araucarez, where they are an inch or two long, have male cones but a fraction of an inch in length. In all the members of the family, excepting Cycas itself, the female fructifications also consist of similarly organized cones bearing a couple of seeds on each scale instead of the numerous pollen sacs. In Cycas the male cones are like those of the other genera, and reach an enormous size; but there are no female cones, for the seeds are borne on special leaflike scales. These are illustrated in fig. 75, which shows also that there are not two seeds (as in the other genera with cones) to each scale, but an indefinite number. The leafy nature of the seed- bearing scale is an important and in- AEN teresting feature. Although theoreti- _ Fis. 75. — Seed-bearing ° cale of Cycas, showing its cally botanists are accustomed to jobeqand leaflike character accept the view that seeds are always ‘ 3 s, Seeds attached on borne on specially modified leaves (sO gither side below the divi- that to a botanist even the ‘‘shell” _ sions of the sporophyil. of a pea-pod and the box of a poppy capsule are leaves), yet in Cycas alone among living plants are seeds really found growing on a large struc- ture which has the appearance of a leaf. Hence, from this point of view (see p. 45, however, for a caution against concluding that the whole plant is similarly lowly organized), Cycas is the most primitive of all the living plants that bear seeds, and hence presumably the likest to the fossil ancestors of the seed-bearing types. In this character it is more primitive than the fossil group of 112 ANCIENT PLANTS the Cordaitee, and comes very close to an intermediate group of fossils to be considered in the next chapter. To enter into the detailed anatomy of the seeds would lead us too far into the realms of the specialist, but we must notice one or two points about them. Firstly, their very large size, for ripe seeds of Cycas are as large as peaches (and peaches, it is to be noted, are fruits, not seeds), and particularly the large size they attain defore they are fer- tilized and have aft embryo. Among the higher plants the young seeds remain very minute until an embryo is secured by the act of fer- tilization, but in the Cycads. the seeds enlarge and lay in a big store of starch in the endosperm before the embryo appears, so that in the cases in which fertiliza- Fig. 76.—Seed of Cycas cut open tion is prevented large, : ” mn, The nucellus, fused at the level 7 to sterile ‘‘seeds” are never- the coat ¢; sc, stony layer of coat; g.c, theless produced. This. pollen chamber in apex of the nucellus; Ss, ‘‘spore’”, filled with endosperm, in which lies the embryo e. must be looked on as a want of precision in the mechanism, and as a waste-_ ful arrangement which is undeniably primitive. An even more wasteful arrangement appears to have been com- mon to the ‘‘seeds” of the Palzozoic period, for, though many fossil ‘‘seeds” are known in detail from the old rocks, not one is known to have any trace of an embryo. A general plan of the Cycas seed is shown in fig. 76, which should be compared with that of Gzxzkgo (fig. 68). The large size of the endosperm and the thick and complex seed-coats are characteristic features of both these structures. Another point that makes the Cycad seeds of special interest is the fact that the male cells (as in Gznkgo) are developed as active, free-swimming PAST HISTORIES OF PLANT FAMILIES 113 sperms, which swim towards the female cell in the space provided for them in the seed (see /.c, fig. 76). The characters of the Cycads as they are now living prove them to be an extremely primitive group, and therefore presumably well represented among the fossils; and indeed among the Mesozoic rocks there is no lack of impressions which have been described as the leaves of Cycads. There is, however, very little reliable material, and practically none which shows good micro- scopic structure. Leaf impressions alone are most un- safe—more unsafe in this group, perhaps, than in: any other—for reasons that will be apparent later on, 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 caution, resulting from the experience of recent discoveries proving many of | these leaves to belong to a different family. There remain, however, many authentic specimens which show that Cycas certainly goes back very far in history, and specimens of this genus are known from the older Mesozoic rocks. We cannot say, however, as securely as used to be said, that the Mesozoic was the “Age of Cycads”, although it was doubtless the age of plants which had much of the external appearance of Cycads. From the Paleozoic we have no reliable evidence of the existence of Cycads, though the plants of that time included a group which has an undoubted connection with them. Indeed, so far as fossil evidence goes, we must sup- pose that the Cycads, since their appearance, possibly at the close of the Palzeozoic, have never been a dominant or very extensive family, though they grew in the past all over the world, and in Europe seem to have remained till the middle of the Tertiary epoch. (0 122) 10 114 ANCIENT PLANTS GHAPTER Ati PAST HISTORIES OF PLANT FAMILIES V. Pteridosperms This group consists entirely of plants which are ex- tinct, and which were in‘the height of their development in the Coal Measure period. As a group they are the most recently discovered in the plant world, and but a few years ago the name “ Pteridosperm” was unknown. They form, however, both one of the most interesting of plant families and one of the most numerous of those which flourished im the Carboniferous period. To mention first the vital point of interest in their structure, they show eaves which in all respects appear like ordinary foliage leaves, and yet bear seeds. ‘These leaves, which we now know bore the seeds, had long been considered as typical fern leaves, and had been named and. described as fern leaves. There are two extremely important results from the discovery of this fossil group, viz. that leaves, to all appearance like ordinary foliage, can’ directly bear seeds, and that the leaves, though like fern leaves, bore seeds like those of a Cycad. As the name Pterzdosperm indicates, the group is a link between the ferns and the seed-bearing plants, and as such is of special interest and value to botanists. The gradual recognition of this group from among the numerous plant fragments of Paleozoic age is one of the most interesting of the accumulative discoveries of fossil botany. Ever since fossil remains attracted the attention of enquiring minds many “ferns” have been recognized among the rich impressions of the Coal Measures. Most of them, however, were not connected with any structural material, and were given many dif- ferent names of specific value. So numerous were these fern ‘‘species” that it was supposed that in the. Coal PAST HISTORIES OF PLANT FAMILIES II5 Measure period the ferns must have been the dominant class, and it is often spoken of even yet as the “ Age of Ferns’. From the rocks of the same age, preserved with their microscopical structure perfect, were stems which were called Lygznodendron. In the coal balls associated with these stems (which were the commonest of the stems so preserved) were also roots, petioles, and Fig. 77.—Sphenopteris Leaf Impression, the fernlike ioliage of Lyginodendron leaflets, but they were isolated, like the most of the fragments in a coal ball, and to each was given its name, with no thought of the various fragments having any connection with each other. Gradually, however, various tragments from the coal balls had been recognized as belonging together; 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 stem, and when leaves were found attached to an isolated fragment of the petiole, the chain of proof was complete that the 116 | ANCIENT PLANTS leaves belonged to the stem, and so on. By a series of lengthy and painstaking investigations all the parts of the plant now called Z yginodendron have been brought together, and the impressions of its leaves have been connected with it, these being of the fernlike type so long called Sphenopterts, illustrated in fig. 7; “The anatomy of the main stem is very up dece of that of a Cycad. The zones of secondary wood are ad : Zs, i fr =. Fig. 78A.—Diagram of the ‘Il ransverse Section of Stem of the Lyginodendron p, Pith; P, primary wood groups; w, secondary wood; /.¢, leaf trace; s, sclerized bands in the cortex; s, longitudinal view of wood elements to show the rows of bordered pits. loosely built, the quantity of soft tissue between the radiating bands of wood, and the size of the pith being large, while from the main axis double strands of wood run out to the leaf base. The primary bundles, how- ever, are not like those of a Cycad stem, but have groups of centripetal wood within the protoxylem, and thus resemble the primary bundles of Poroxylon (see p. 97), which are more primitive in this respect than those of the Cycads. PAST HISTORIES OF PLANT FAMILIES T17 The roots of Lygznodendron, when young, were like those of the Marattiaceous ferns, their five-rayed mass of wood being characteristic of that family, and different from the type of root found in most other ferns (cf. fig. 788 with fig. 35 on p. 60). Unlike fern roots of any kind, however, they have well-developed zones of secondary % . FZ ra g > men r i ie CS baa = ae ~- ye | ad od uk %. Fabs - wf ae Ps Fig. 788.—Transverse Section of Root of Lyginodendron w, Five-rayed mass of primary wood; s, zone of secondary wood; «¢, cortical and other soft tissues. wood, in which they approach the Gymnospermic roots (see fig. 788, s). A further mixture of characters is seen in the vascular bundles of the petioles. A double strand, like that in the lower Gymnosperms, goes off to the leaf base from the main axis, but in the petiole itself the bundle is like a normal fern stele, and shows no characters in transverse section which would separate it from the ferns. Such a petiole is illustrated in fig. 79, with its V-shaped fernlike stele. On the petioles and stems were certain rough, spiny structures of the nature of complex hairs. In some 118 ANCIENT PLANTS cases they are glandular, as is seen in g in fig. 79, 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 plant. As is seen from fig. 77, the leaves were quite fern- like, but in structural specimens they have been found with the characteristic glandular hairs of the plant. The seeds were so long known under the name of Lageno- stoma that they are still -called, by 1¢ though they have been identified as belonging to Lygzzo- dendron. They were small (about 4 in. in maximum length) when compared with those of most other plants of the group, or of the Cycads, with which they show considerable affinity. They are too com- v, Fern-like stele; c, cortex; g, glandular hairlike plex to describe fully, protuberances. and have been men- tioned already (see p. 76), so that they will not be described in much detail here. The diagrammatic figure (fig. 56) shows the essential characters of their longitudinal section, and their transverse section, as illustrated in fig. 80, shows the complex and elaborate mechanism of the apex. Round the ‘“‘seed” was a sheath, something like the husk round a hazel nut, which appears to have had the function of a protective organ, though what its real morphological nature may have been is as yet an un- solved problem. On the sheath were glandular hairs Fig. 79.—Transverse Section through Petiole of Lyginodendron PAST HISTORIES OF PLANT FAMILIES 119 like those found on the petiole and leaves, which were, indeed, the first clues that led to the discovery of the connection between the seed and the plant Lygznoden- dron. The pollen grains seem to have been produced in sacs very like fern sporangia developed on normal foliage leaves, each grain entered the cavity fc in the seed (see fig. 56), but of the nature of the male cell we are ignorant. In none of the fossils has any embryo been found in the “seeds”, so that presumably they ripened, or at least matured their tissues, before fertilization. These, in a few words, are the essentials of the struc- tures of Lygznodendron. But this plant is only one of a group, and at least two other Fig. 80.—Diagram of Transverse Sec- of the Pteridosperms deserve tion of Lagenostoma Seed near the Apex, ’ : ° F showing the nine flutings / of the coat notice, V1Z. Medullosa, which ¢; uv, the vascular strand in each; z¢, is more complex, and Heler- _ cone of nucellar tissue standing up in angium, which is simpler than 1 fut ape he mcs the central type. grains; s, space between nucellus and Heterangium iS found also coat. Compare with diagram 56. in rocks rather older than the coal series of England, though of Carboniferous age, viz. in the Calciferous sandstone series of Scotland, it occurs also in the ordinary Coal Measure nodules It is in several respects more primitive than Lygznoden- dron, and in particular in the structure of its stele comes nearer to that of ferns. The stele is, in fact, a solid mass of primary wood and wood parenchyma, corresponding in some degree to the protostele of a simple type (see p. 61, fig. 36), but it has towards the outside groups of protoxylem surrounded by wood in both centripetal and centrifugal directions, which are 120 ANCIENT PLANTS just like the primary bundles in Lyginodendron. Out- side the primary mass of wood is a zone of secondary wood, but the quantity is not large in proportion to it (see fig. 81), as is common in Lyginodendron. - Though the primary mass is so fernlike in appearance the larger tracheids show series of bordered pits, as do most of the tracheids of the Pteridosperms, in which they show a Gymnosperm-like character. MALY Os an aa) soy meta ; ts es i> Bes +, e B Ld px. ass ca? a | = Ww DRRERYGEE 5 Nees Se S 2eS3 pees A ws a N = Ss >. y eS eaeice N tose a5 == “ae : ‘3 < . aN p. Va NY We) roe x sel may Fig. 81..—Heterangium A, Half of the stele of a stein, showing the central mass of wood s mixed with parenchyma g. ‘The protoxylem groups #. x. lie towards the outside of the stele. Sur- rounding it is the narrow zone of small-celled secondary wood w. B, A few of the wood cells in longitudinal view: ~.x., Protoxylem; #, parenchyma. s, Large vessels with rows of bordered pits. The foliage of Heterangzum was fernlike, with much- divided leaves similar to those of Lygznodendron. We have reason to suspect, though actual proof is wanting as yet, that small Gymnosperm-like seeds were borne directly on these leaves. _Medullosa has been mentioned already (see p. 72) because of the interesting ‘and unusually complex type of its vascular anatomy. Each individual stele of the group of three in the stem, however, is essentially similar to the stele of a Heterangium. PAST HISTORIES OF PLANT FAMILIES 121 Though the whole arrangement appears to differ so widely from other stems in the plant world, careful comparison with young stages of recent Cycads has indicated a possible remote connection with that group, while in the primary arrangements of the Bieler rs a likeness may be traced to * the ferns. The roots, even in their primary tssues, were like those of Gymnosperms, but the foliage with its compound leaves was quite fern-like externally. of the essential characters of such ancestral plants, but here the realm of fossil botany ceases, to give place to theoretical speculation. As a fact, there is a deep abyss between the ferns and the other families of the Pterido- Fas. HISTORIES OF PLANT FAMILIES 134 phytes, which is not yet bridged firmly enough for any but specialists, used to the hazardous footing on such structures, to attempt to cross it. 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 journey. In the Coal Measures and previous periods we see the ferns already represented by two large families, differing greatly from each other, and from the main families of modern ferns which sprung at a later date from some stock which we have not yet recognized. But though their past is so obscure, the palzeozoic ferns, and their allies throw a brilliant light on the course of evolution of the higher groups of plants, and the gulf between ferns and seed-bearing types may be said to be securely bridged by the Botryopterideze’ and the Pteridosperms. CHAPTER. XIV PAST HISTORIES OF PLANT FAMILIES VII. The Lycopods The present-day members of this family are not at all impressive, and in their lowliness may well be over- looked by one who is not interested in unpretending plants. The fresh green mosslike Se/agznella grown by florists as ornamental borders in greenhouses and the creeping “club moss” twining among the heather on a Highland moor are probably the best known of the living representatives of the Lycopods. In the past the group held a very different position, and in the distant era of the Coal Measures it held a dominant one. Many of the giants of the forest belonged to the family (see fron- tispiece), and the number of species it contained was very great. 134. ANCIENT PLANTS Let us turn at once to this halcyon perioa of the group. The history of the times intervening between it and the present is but the tale of the dying out of the large species, and the gradual shrinking of the family and dwarfing of its representative genera. It is difficult to give the characters of a scientific family in a few simple words; but perhaps we may describe the living Lycopods as plants with creeping stems which divide and subdivide into two with great regularity, and which bear large numbers of very small pointed leaves closely arranged round the stem. The fruiting organs come at the tips of the branches, and sometimes themselves divide into two, and in these cone-like axes the spore cases are arranged, a single one on the upper side of each of the scales (see p. 67, fig. 46, A). In the Lycopods the spores are all alike, in the Selaginellas there are larger spores borne in a small number (four) i in some sporangia (see fig. 53, p. 75), and others in large numbers and of smaller size on the scales above them. The stems are all very slender, and have no zones of secondary wood. They generally creep or climb, and from them are put out long structures some- thing like roots in appearance, which are specially modi- fied stem-like organs giving rise to roots. From the fossils of the Coal Measures Lepzdodendron must be chosen as the example for comparison. The different species of this genus are very numerous, and the various fossilized remains of it are among the com- monest and best known of paleontological specimens. — The huge stems are objects of public interest, and have been preserved in the Victoria Park in Glasgow in their original position in the rocks, apparently as they grew with their spreading rootlike organs running horizon- tally. A great stump is also preserved in the Man- chester Museum, and is figured in the frontispiece. While among the casts and impressions the leaf bases of the plant are among the best preserved and the most beautiful (see fig. 93). The cone has already been illus- PAST HISTORIES OF PLANT FAMILIES E25 trated (see fig. 46 and fig. 9), and is one of the best known of fossil fructifications. From the abundant, though scattered material, fossil botanists have reconstructed the plants in all their detail. The trunks were lofty and of great thickness, bearing Fig. 93.—Photo of Leaf Bases of Lepzdodendron C, Scar of leaf; ‘Ss, leaf base. In the scar: v, mark of severed vascular bundle, and p, of parichnos. JZ, Ligule scar. towards the apex a much-branched crown, the branches, even down to the finest twigs, all dividing into two equal parts. The leaves, as would be expected from the great size of the plants, were much bigger than those of the recent species (fig. 93 shows the actual size of the leaf bases), but they were of the same relatively small size as compared with the stems, and of the same simple 136 ANCIENT PLANTS pointed shape. A transverse section across the apex of a fertile branch shows these closely packed leaves arranged in series round the axis, those towards the outside show the central vascular strand which runs through each. The markings left on the well-preserved leaf-scars ® = a lh ge. . Rake >. « ‘. pe o ag . & ~, te ‘ a Qr- ( % 22 p Fig. 94.—Section across an Axis surrounded by many Leaves, which shows their simple shape and single central vascular bundle vw indicate the main features of the internal anatomy of the leaves. They had a single central vascular strand (z, fig. 93), on either side of which ran a strand of soft tissue ~ called the parichnos, which is characteristic of the plants of this group. While another similarly ob- scure structure associated with the leaf is the little scale- like ligule 7 on its upper surface. The anatomy of the stems is interesting, for in the PAST HISTORIES OF PLANT FAMILIES re different species different stages of advance are to be found, from the simple solid protostele with a uniform mass of wood to hollow ring steles with a pith. An interesting intermediate stage between these two is found in Lepidodendron selaginoides (see fig. 95), where the central cells of the wood are not true water-conducting Fig. 95.—Transverse Section of Lepzdodendron selaginoides, showing the circular mass of primary wood, the central cells of which are irregular water-storage tracheides s, Zone of secondary wood; ¢, inner cortical tissues; 7, intrusive burrowing rootlet ; oc, outer cortical tissues with corky external layers 2. (Microphoto.) cells, but short irregular water-storage tracheides (see p. 56), which are mixed with parenchyma. All the genera of these fossils have a single central stele, round which it is usual to find a zone of secondary wood of greater or less extent according to the age of the plant. Some stems instead of this compact central stele have a ring of wood with an extensive pith. Such a type is illustrated in fig. 96, which shows but a part of the circle of wood, and the zone of the secondary wood outside it, 138 ANCIENT PLANTS which greatly exceeds the primary mass in thickness. This zone of secondary wood became very extensive in old stems, for, as will be imagined, the primary wood was not sufficient to supply the large trunks. 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-day. This is the Fig. 96.—A, Lepi- dodendron Stem with Hollow Ring of Wood w and Zone of Secondary Wood s. B, Longitudinal View of the Narrow. Pits of the Wood Elements. most important difference between the living and the fossil stems of the family, for no living plants of the family have such secondary wood. On the other hand, the individual elements of this wood are different from those of the higher families hitherto considered, and have narrow slit-like pits separated by bands of thicken- ing on the longitudinal walls. Such tracheides are found commonly in the Pteridophytes, both living and fossil. Their type is seen in fig. 96, B, which should be com- pared with that in figs. 78, A and 62, B to see the con- trast with the higher groups. | PAST HISTORIES OF PLANT FAMILIES 139 To supply the vascular tissues of the leaf traces, simple strands come off from the outer part of the pri- mary wood, where groups of small-celled protoxylem project (see fx in fig. 97). The leaf strands 7¢ move out through the cortex in considerable numbers to supply the many leaves, into each of which a single one enters. Fig. 97.—Transverse Section of Outer Part of Primary Wood of Lepizdodendron, showing #x, projecting protoxylem groups; /¢, leaf trace coming from the stele and passing (as 7#) through the cortex As regards the fructifications of Lepzdodendron much could be said were there space. The many genera of Lepidodendron bore several distinct types of cones of different degrees of complexity. In several of the. genera the cones were simple in organization, directly comparable with those of the living Lycopods, though on a much larger scale (see p. 67). In some the spores were uniform, all developing equally in numerous tetrads. The sporophyll was radially extended, and along it the 140 ANCIENT PLANTS large sausage-shaped sporangia were attached (see fig. 98). The tips of the sporophylls overlapped and afforded protection to the sporangia. The axis of the cone had a central stele with wood elements like those in the stem. The appearance of a transverse section of an actual cone is shown in fig. 99. Here the sporangia are irregular in shape, owing to their contraction after | ripeness and during fossilization. | Other cones had sporangia similar in size and shape, but which pro- duced spores of two kinds, large ones re- sulting from the ripen- ing of only two or three tetrads in the lower sporangia, and numerous small ones in the — sporangia above. The similarity be- Fig. ¢8.— Longitudinal Diagram, showing the tween the Lepidoden- arrangement of the elongated sporangia on the sporophylls dron and the modern a, Main axis, round which the sporophylls are in- Lycopod cone has serted; S, sporangium; s, leaflike end of sporophyll. been pointed out ale ready (p. 67), and it is this which forms the principal guarantee that they belong to the same family, though the size and wood development of the palzozoic and the modern plants differ so greatly. 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 construction. This type was described on p. 75, fig. 54, in a series of female fructifications, so that its essential structure need not be recapitulated. ’ PAST HISTORIES OF PLANT FAMILIES 141 Fig. 99.—Transverse Section through Cone of Lepidodendron A, Main axis with woody tissue; s¢, stalks of sporophylls cut in oblique longi- tudinal direction; s, tips of sporophylls cut across; s, sporangia with a few groups of spores. (Microphoto.) The section shown in fig. 100 is that cut at right angles to that in which the spo- rangia are shown in fig. 98, viz. tangential to the axis. A remark- able feature of the plant is that there were also round those spo- rangia which bore the numerous small spores (corresponding to pollen grains) enclosing integu- ment-like flaps similar to those shown in fig. 100, sf. f. This type of fructification is the nearest approach to seed and pollen grains reached by any of the Pteridophytes, and its appear- ance at a time when the Lycopods were one of the dominant’ families Fig. 100.—Section through one Sporangium of Lepidocarpon 5p, Sporophyll; sf./, flaps of sporophyll protecting sporan- gium; S, large spore within the sporangium wall w; s, the three aborted spores of the tetrad to which s belongs. 142 ANCIENT PLANTS is suggestive of the effect that such a position has on the families occupying it, however lowly they may be. The simple Pteridophyte Lycopods had not only the tall trunks and solid woody structure of a modern tree, but also a semblance of its seeds. Whether this line of development ever led on to any of the higher families is still uncertain. The feeling of most specialists is that it did not; but there are not wanting men who support the view that the lycopod affinity evolved in time and entered the ranks of the higher plants, and indeed there are many points of superficial likeness between the paleeozoic Lycopods and the Conifere. Judged from their internal structure, however, the series through the ferns and Pteridosperms leads much more convincingly to the seed plants. In their roots, or rather in the underground struc- tures commonly called roots, the Lepidodendrons were also remarkable. Even more symmetrically than in their above-ground branching, the base of-their trunks divided; there were four main large divisions, each of which branched into two and these into two again. These structures were called Stzgmarza, and were com- mon to all species of Lepzdodendron and also the group of Szgillaria (see fig. 102). On these horizontally running structures (well shown in the frontispiece) small append- ages were borne all over their surface in great profusion, which were, both in their function and microscopic struc- ture, rootlets. They left circular scars of a characteristic appearance on the big trunks, of which they were the only appendages. . These scars show clearly on the fragments along the ledge to the left of the photograph. The exact morphological nature of the big axes is not known; their anatomy is not like that of roots, but is that of a stem, yet they do not bear what practically every stem, whether underground or not, has developed, namely leaves, or scales representing reduced leaves. Their nature has been commented on previously (p. 69), and we cannot discuss the point further, but must be PAST HISTORIES OF PLANT FAMILIES 143 content to consider them as a form of root-bearing stem, practically confined to the Lycopods and _ principally developed among the palzozoic fossils of that group. In microscopic structure the rootlets are extremely well known, because in their growth they have pene- trated the masses of the tissues of other plants which were being petrified and have become petrified with them. The mass of decaying vegetable tissue on which the living plants of the period flourished were every- where pierced by these intrusive rootlets, and they are found petrified inside other- wise perfect seeds, in the peo FTE SELES hearts of woody stems, in SEAS leaves and sporangia, and sometimes even inside each & Gs , other! Fig. 95 shows such gv roa BED ac a root 7 lying in the space id 7 left by the decay of the soft tissue of the inner cortex in an otherwise excellently pre- wv served 7 epido dendron stem Fig, 101.—Transverse Section through a Rootlet of Stzgmaria (see also fig. ror). In fig. nee : A oc, Outer cortex; s, space; zc, inner Io! their simple structure cortex; w, wood of vascular strand (wood is seen. They are often ex- only preserved); gx, protoxylem group. tremely irregular in shape, owing to the way they seem to have twisted and flat- tened themselves in order to fit into the tissues they were penetrating. No root hairs seem to have been developed in these rootlets, but otherwise their structure is that of a typical simple root, and very like the swamp- penetrating rootlets of the living Isoetes. | The Stigmarian axes and their rootlets are very commonly found in the “underclays” and ‘“‘gannister ” beds which lie below the coal seams (see p. 25), and they may sometimes be seen attached to a bit of the trunk growing upwards through the layers. They and the aerial stems of Lepidodendron are perhaps the commonest and most widely known of fossil plants. 144 ' ANCIENT PLANTS Before leaving the paleeozoic Lycopods another genus must be mentioned, which is also a widely spread and important one, though it is less well known than its con- temporary. The genus Szgz//aria is best known by its impressions and casts of stems covered by leaf scars. The stems were sometimes deeply ribbed, and the leaf scars were arranged in rows and were more or less hexa- allege € ; Fig. 102.—Cast and Reverse of Leaf Scars of Sigi//aria. In A the shape of the leaf bases is clearly shown, the central markings in each being the scar of the vascular bundle and parichnos gonal in outline, as is seen in fig. 102, which shows a cast and its reverse of the stem of a typical Szgz//aria. In its primary wood Szgzdarza differed from Lepido- _dendron in being more remote from the.type with a primary solid stele. Its woody structure was that of a ring, in some cases irregularly broken up into crescent- shaped bundles. The secondary wood was quite similar to that of Lepzdodendron. Stigmaria and its rootlets belong equally to the two plants, and hitherto it has been impossible to tell whether PAST HISTORIES OF PLANT FAMILIES 145 any given specimen of Szzemarza had belonged to a Lepidodendron or a Sigtllaria. Between the two genera there certainly existed the closest affinity and similarity in general appearance. These two genera represent the climax of develop- ment of the Lycopod family. In the Lower Mesozoic some large forms are still found, but all through the Mesozoic periods the group dwindled, and in the Ter- tiary little is known of it, and it seems to have taken the retiring position it occupies to-day. GCHAPTER. XV PAST HISTORIES OF PLANT FAMILIES VIII. The Horsetails The horsetails of to-day all belong to the one genus, E-quisetum, among the different species of which there is a remarkably close similarity. Most of the species love swampy land, and even grow standing. up through water; but some live on the dry clay of ploughed fields. Wherever they grow they usually congregate in large numbers, and form little groves together. They are easily recognized by their delicate stems, branching in bottle-brush fashion, and the small leaves arranged round them in whorls, with their narrow teeth joined to a ring at the base. At the end of some of the branches come the cones, with compactly arranged and simple sporophylls all of one kind. In England most plants of this family are but a few inches or a foot in height, though one species sometimes reaches 6 ft., while in South America there are groves of delicate-stemmed plants 20 ft. high. The ribbed stems and the whorls of small, finely toothed leaves are the most important external charac- (0 122) 12 146 ANCIENT PLANTS teristics of the plants, while in their internal anatomy | the hollow stems have very little wood, which is arranged in a series of small bundles, each associated with a hollow canal in the ground tissue. The family stands apart from all others, and even between it and the group of Lycopods there seems to be a big gap across which stretch no bonds of affinity. Has the group always.been in a similar position, and stood isolated in a backwater of the stream of plant life? In the late Tertiary period they seem to have held much the same _ posi- tion as they do now, and we learn nothing new of them from rocks of that age. When, however, we come to the Mesozoic, the members of the family are Fig. 103.—Impression of Leaf Whorl. of greater SIZe, though they of Lguisetites from the Mesozoic Rocks, toca d f. th : showing the narrow toothed form of the appear ( O ju ge rom e1r leaves. (Photo.) external appearance) to have been practically iden- tical with those now living in all their arrangements. In some beds their impressions are very numerous, but unfortunately most are without any indication of internal structure. Fossils from the Mesozoic are called Aguzse- tites, a name which indicates that they come very close to the living ones in their characters. In the Lower Mesozoic some of these stems seem to have reached the great size of a couple of feet in circumference, but to have no essential difference from the others of the group. : When, however, we come to the Palaeozoic rocks we find many specimens with their structure preserved, and we are at once in a very different position as regards the family. 3 First in the Permian we meet with the important PAST HISTORIES OF PLANT FAMILIES 147 genus of plant called Ca¢amztes, which were very abundant in the Coal Measures. Many of the Calamites were of great size, for specimens with large trunks have been found 30 ft. and more long, which when growing must certainly have been much taller than that. The number of individuals must also have been very great, for casts and impressions of the genus are among the commonest Fig. 104.—Small Branches attached to stouter Axis of Ca/amites. Photo of Impression fossils. They were, in fact, one of the dominant groups of the period. Like the Lycopods, the Equisetacez reached their high-water mark of development in the Carboniferous period; at that time the plants were most numerous, and of the largest size and most complicated structure that they ever attained. As will be immediately. suspected from analogy with the Lycopods, they differed from the modern members of the family in their strongly developed anatomy, and in the strength and quantity of their secondary wood. 148 ANCIENT PLANTS Yet in their externa] appearance they probably resembled the living genus in all essentials, and the groves of the larger ones of to-day growing in the marshes probably have the appearance that the palzozoic plants would have had if looked at through a reversed opera glass. Fig. 104 is a photograph of some of the “small branches of a pani in which the ribbed stem can be seen, and on the small side twigs the fine, pointed leaves lying in whorls. In most of the fossilspecimens, how- ever, particularly the larger ones, the ribs are not those of the true surface, but are those marked on the enternal cast of the pith. Among tissue petrifactions there Fig. 105.—Transverse Section of Calamites Stem : with Secondary Wood w formed in Regular Radial are many Calamite Rows in a Solid Ring stems of various c, Canals associated with the primary bundles; #, stages of growth. In cells of the pith, which 1s hollow with a cavity 72. S o cor, Cortex and outer tissues well preserved. (Micro- the VOT) ORES oe photo. ) there are only pri- mary bundles, and these little stems are like those of a living Equisetum in their anatomy, and have a hollow pith and small vascular bundles with canals associated. The fossil forms, how- ever, soon began to grow secondary wood, which devel- oped in regular radial rows from a cambium behind the primary bundles and joined to a complete ring. A stem in this stage of development is seen in fig. 105, where only the wood and internal tissues are preserved. The very characteristic canals associated with the primary bundles are clearly shown. The amount of secondary PAST HISTORIES OF PLANT FAMILIES 149 wood steadily increased as the stems grew (there appear to have been no “annual rings”) till there was a very large quantity of secondary tissue of regular texture, through which ran small me- dullary rays, so that the stems became increasingly like those of the higher plants as they grew older. It is the primary structure which is the impor- tant factor in considering their affinity, and that is essentially the same as in the other members of the family in which secondary thickening is not Fig. 106.—Diagram of developed. As we have seen already the Arrangement of the : . Bundles at the Node of a in other groups of fossils, secondary Cyjamite,. showing how wood appears to develop on similar _ those of consecutive in- lines whenever it is needed in any ‘modes alternate group, and therefore has but little value n, Region of node as an indication of systematic position. This important fact is one, however, which has only been realized as a result of the study of fossil plants. The longitudinal section of the stems, when cut tan- gentially, is very charac- teristic, as the bundles run straight down to each node and _ there divide, the neighbouring halves joining so that the bundles of each node alternate with those of the ones above and be- Fig. 107.—Leaf of Calamites in Cross Section spe ces ng. ig. ; Sopot The leaves which v, Vascular bundles; s, cells of sheath, filled ? ; with blackened contents; 4, palisade cells; eee attached at the e, epidermis. nodes were naturally much larger than those of the present Equisetums, though they were similarly simple and undivided. Their anatomy is preserved in a number of cases (see fig. 107), and was simple, with 150 | ANCIENT PLANTS a single small strand of vascular tissue lying in the centre. They had certain large cells, sometimes very black in the fossils, which may have been filled with mucilage. The young roots of these plants have a very charac- teristic cortex, which consists of cells loosely built to- gether in a lacelike fashion, with large air spaces, so that they are much like water plants in their appearance Fig. 108.—Transverse Section of Young Fig. 109.—Diagram of Cone of Root of Calamites Calamites w, Wood of axis; Z7, spaces in the lacunar A, Main axis; 67, sterile bracts; cortex, whose radiating strands 7 are some- Sp, sporophylls with four sporangia what crushed; ex, outermost cells of cortex S attached to each, of which two with thickened wall. only are seen. " (see fig. 108). “Indeed, so unlike the old roots and the name and supposed to be submerged stems, but thej connection with Cadamites is now quite certain. As their. wcody axis develops, the secondary tissue increases and’: pushes off the lacelike cortex, and the roots become very similar in their anatomy to the stems. Both have similar zones of secondary wood, but the roots do not have those primary canals which are so characteristic of the stems, and thereby they can be readily distinguished from them. The fructifications of the Calamites were not unlike those of the living types of .the family, though in some > Ay) stems are they, that for long they were called by another |. PAST HISTORIES OF PLANT FAMILIES I5I respects slightly more complex. Round each cone axis developed rings of sporophylls which alternated with sterile sheathing bracts. Each sporophyll was shaped like a small umbrella with four spokes, and stood at right angles to the axis, bearing a sporangium at each Fig. 110.—Longitudinal Section of Part of Ca/amites Cone ér, Sterile bracts attached to axis; sf, attachment of sporophylls; Ss, sporangia. At X a group of four sporangia is seen round the sporophyll, which is seen at a. (Microphoto. ) of the spokes. ont Fig. 114.—Sphenophyllum, Transverse Section with Secondary Wood w. At ¢ the cork formation is to be seen. (Microphoto.) out radially through the wood, such as are found in all other zones of secondary wood, and in this arrange- ment of soft tissue the plants are unique. Fig. 115.-—Group of Wood Cells w, showing their shape and the small soft- walled cells at the angles between them # remarkable for the Beyond the wood was a zone of soft tissue and phloem, which is not often preserved, while out- side that was the cork, which added to the cortical tissues as the stem grew (see fig. 114, ¢). Petrified material of leaves and roots is rare, and both are chiefly known through the work of the French _palzobotanist Renault. The leaves are chiefly bands of sclerized strengthening tissue, and generally had the structure of aerial, not can) submerged leaves. “The roots were simple in structure, PAST HISTORIES OF PLANT FAMILIES 157 and, as in Calamites, had secondary tissue like that in the stems. In the case of the fructifications it is tHe English material which has yielded the most illuminating speci- mens. The cones were long and slender, externally covered by the closely packed tips of the scales, which overlapped deeply. Between the whorls of scales lay the sporangia, attached to their upper sides by slender stalks. A diagram will best explain how they were ar- ranged (see fig. 116). Two sporangia were attached to each bract, but their stalks were of different lengths, so that one sporangium lay near the axis and one lay outside it toward the tip of the bract. In its anatomy the stalk of the cone has certain features similar to those in the stem proper, which were among the first indications that led Se to the discovery that the cone Fig. 116.—Diagram of Arrangement belonged to Sphenophyllum. piseseilin i There eee erOUS Spores A, Axis; dr, bract; S, sporangium, in each of the sporangia, with stalk sé. which had coats ornamented with little spines when they were ripe (fig. 117, if ex- amined with a magnifying glass, will show this). Hither- to the only spores known are of uniform size, and there is no evidence that there was any differentiation into small (male) and large (female) spores such as were found in some of the Lepidodendrons. In this respect Sphenophyllum was less specialized than either Lefzdo- dendron or Calamites. — In the actual sections of Sphenophyllum cones the numerous sporangia seem massed together in confusion, but usually some are cut so as to show the attachment 158 ANCIENT PLANTS of the stalk, as in fig. 117, st. As the stalk was long and slender, but a short length of it is usually cut through in any one section, and to realize their mode of attach- ment to. the axis (as shown in fig. 116) it is necessary to study a series of sections. Of the other plants belonging to the group, Low- manites Rodmert is specially interesting. Its sporangia Fig. 117.—Part of Cone of Sphenophyllum, showing sporangia sf, some of which aré cut so as to show a part of their stalks s¢. 8B, Bract. (Microphoto.) were borne on stalks similar to those of Sphenophyllum, but each stalk had two sporangia attached to it. Two sporangia are also borne on each stalk in S. /fertzde. These plants help in elucidating the nature of the stalked sporangia of Sphenophyllum, for they seem to indicate a direct comparison between them and the sporophylls of the Equisetales. | : There is, further, another plant, of which we only know the cone, of still greater importance. This cone PAST HISTORIES OF PLANT FAMILIES 159 (Chetrostrobus) is, however, so complex that it would take far too much space to describe it in detail. Even a diagram of its arrangements is extraordinarily ela- borate. To the specialist the cone is peculiarly fas- cinating, for its very complexity gives him great scope for weaving theories about it; but for our purposes most of these are too abstruse. Its most important features are the following. Round Fig. 118.—A, Diagram of Three-lobed Bract from Cone of Cheirostrobus. a, Axis; br, the three sterile lower lobes of the bract; sf, the three upper sporophyll-like lobes, to each of which were attached four sporangia s. B, Part of the above seen in section longitudinal to the axis. (Modified from Scott.) the axis were series of scales, twelve tn each whorl, and each scale was divided into an upper and a lower por- tion, each of which again divided into three lobes. The lower three of each of these scale groups were sterile and bractlike, comparable, perhaps, with the bracts in fig. 116; while the upper three divisions were stalks round each of which were four sporangia. Each sporo- phyll segment thus resembled the sporophyll of Cada- mites, while the long sausage-shaped sporangia them- 160 ANCIENT PLANTS selves were more like those of Lepedodendron. In fig. 118 is a diagram of a trilobed bract with its three attached sporophylls. Round the axis were very numer- ous whorls of such bracts, and as the cone was large there were enormous numbers of spore sacs. A point of interest is the character of the wood of the main axis, which is similar to that of Lepidoden- dron in many respects, being a ring of centripetally developed wood with twelve projecting external points of protoxylem. This cone? is the most complex fructification of any of the known Pteridophytes, whether living or fossil, which alone ensures it a special importance, though for our purpose the mixed affinities it shows are of greater interest. To mention some of its characters:—The individual segments of the sporophylls, each bearing four sporangia, are comparable with those of Cadamztes, while the indi- vidual sporangia and the length of the sporophyll stalk are similar in appearance to those of Lepzdodendron. The wood of the main axis also resembles that of a typical Lepidodendron, ‘The way the vascular bundles of the bract pass out from the axis, and the way the stalks bearing the sporangia are attached to the sterile part of the bracts, are like the corresponding features in. Sphenophyllum, and still more like Bowmanites. Many other points of comparison are to be found in these plants, but without going into further detail enough has been indicated to support the conclusion that Cheerostrobus is a very important clue to the affinities of the Sphenophyllales and early Pteridophytes. It is indeed considered to have belonged to an ancient stock of plants, from which the Equisetacez, and SAheno- phyla, and possibly also the Lycopods all sprang. Sphenophyllum, Bowmanites, and Chetrostrobus, a series of forms that became extinct in the Palzozoic, remote in their structure from any living types, whose 1 For fuller description of this interesting cone, see Scott’s Studies, p. 114 e¢ seq. PAST HISTORIES OF PLANT FAMILIES 161 existence would have been entirely unsuspected but for the work of fossil botany, are yet the clues which have led to a partial solution of the mysteries surrounding the present-day Lycopods and Equisetums, and which help to bridge the chasm between these remote and degenerate families. : CHAPTER XVII PAST HISTORIES OF PLANT FAMILIES X. The Lower Plants In the plant world of to-day there are many families including immense numbers of species whose organiza- tion is simpler than that of the groups hitherto con- sidered. Taken all together they form, in fact, a very large proportion of the total number of living species, though the bulk of them are of small size, and many are microscopic. | These ‘lower plants” include all the mosses, and the flat green liverworts, the lichens, the toadstools, and all the innumerable moulds and parasites causing plant diseases, the green weeds growing in water, and all the seaweeds, large and small, in the sea, the minute green cells growing in crevices of the bark of trees, and all the similar ones living by millions in water. Truly a host of forms with an endless variety of structures. Yet when we turn to the fossil representatives of this formidable multitude, we find but few. Indeed, 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 considered. The reasons for this dearth of fossils of the lower types are not quite apparent, but one which may have some bearing on it is the difficulty of mineralization. It is self-evident that the more delicate and soft-walled any structure is (c 122) 13 162 ANCIENT PLANTS the less chance has it of being preserved without decay long enough to be fossilized. As will have been under- stood from Chapter II, even when the process of fossiliza- tion took place, geologically speaking, rapidly, it can never have been actually accomplished quickly as com- pared with the counter processes of decay. Hence all the lower plants, with their soft tissue and lack of wood and strengthening cells, seem on the face of it to stand but little chance of petrifaction. There is much in this argument, but it is not a sufficient explanation of the rarity of lower plant fossils. All through the preceding chapters mention has been made of very delicate cells, such as pith, spores, and even germinating spores (see fig. 47, p. 68), with their most delicate outgrowing cells. If hie such small and delicate elements from the higher plants are preserved, why should not many of the lower plants (some of which are large and sturdy) be found in the rocks? ° As regards the first group, the mosses, it is probable that they did not exist in the Palaeozoic period, whence our most delicately preserved fossils are derived. There seems much to support the view that they have evolved comparatively recently although they are less highly organized than the ferns. Quite recently experiments have been made with their near allies the liverworts, and those which were placed for one year under conditions similar to those under which plant petrifaction took place, were found to be perfectly preserved at the end of the period; though they would naturally decay rapidly under usual conditions. This shows that Bryophyte cells are not peculiarly incapable of preservation as fossils, and adds weight to the negative evidence of the rocks, strengthening the presumption of their late origin. That some of the lower plants, among the very lowest and simplest, can be well preserved is shown in the case of the fossil fungi which often occur in micro- scopic sections of palzozoic leaves, where they infest the higher plants as similar parasitic species do to-day. / PAST HISTORIES OF PLANT FAMILIES 163 We must now bring forward the more important of the facts known about the fossils of the various groups of lower plants. Bryopuytes.—JVosses. Of this family there are no specimens of any age which are so preserved as to show their microscopical structure. Of impressions there are a few from various beds which show, with more or less uncertainty in most cases, stems and leaves of what appear to be mosses similar to those now extant, but they nearly all lack the fructifications which would deter- mine them with certainty. These impressions go by the name of Muscztes, which is a dignified cloak for ignorance in most cases. The few which are quite satis- factory as impressions belong to comparatively recent rocks. Liverworts are similarly scanty, and there is nothing among them which could throw any light on the living forms or their evolution. The more common are of the same types as the recent ones, and are called JZar- chantites, specimens of which have been found in beds of various ages, chiefly, however, in the more recent periods. of the earth’s history. It is of interest to note that among all the delicate tissue which is so well preserved in the ‘coal balls” and other palzozoic petrifactions, there are no specimens which give evidence of the existence of mosses at that time. It is not unlikely that they may have evolved more recently than the other groups of the “lower” plants. CuHARACE2.—Members of this somewhat isolated family (Stoneworts) are better known, as they fre- quently occur as fossil casts. This is probably due to their character, for even while alive they tend to cover their delicate stems and leaves, and even fruits, with a limy incrustation. This assists fossilization to some degree, and fossil Charas are not uncommon. Usually they are from the recently deposited rocks, and the 164 ANCIENT PLANTS earliest true Charas date only to the middle of the Mesozoic. An interesting occurrence is the petrifaction of masses of these plants together, which indicate the existence of an ancient pool in which they must have grown in abun- dance at one time. A case has been described where masses of Chara are petrified where they seem to have been growing, and in their accumulations had gradually filled up the pond till they had accumulated to a height of 8 feet. The plants, however, have little importance from our present point of view. Funer.—Of the higher fungi, namely, ‘“ toadstools ”, we have no true fossils. Some indications of them have _ been found in amber, but such speci- mens are so unsatisfactory that they can hardly afford much interest. The lower fungi, however, and in particular the microscopic and parasitic forms, occur very fre- quently, and are found in the Coal Measure fossils. Penetrating the tissues of the higher plants, their hosts, the parasitic cells are often OND excellently preserved, and we may ree uo The Hyphe of see their delicate hyphz wander- ungi Parasitic on a Woody . : , Tree ing from cell to cell as in fig. 1109, 6, Cells of host; # hyphae of While sometimes there are attached fungus, with dividing cell walls. SWOllen cells which seem to be sporangia. From the Palaeozoic we get leaves with nests of spores of the fungus which had attacked and spotted them as so many do to leaves to- day (see fig. 120). What is specially noticeable about these plants is their similarity to the living forms infest- ing the higher plants of the present day. Already in the Paleozoic the sharp distinction existed between the PAST HISTORIES OF PLANT FAMILIES 165 highly organized independent higher plants and their simple parasites. The higher plants have changed pro- foundly since that time, stimulated by ever-changing surroundings, but the parasites living within them are now much as they were then, just sufficiently highly organized to rob and reproduce. A form of fungus inhabitant which seems to be useful to the higher plant appears also to have existed in Paleozoic times, viz. JZycorhiza. In the roots of many living trees, particularly such as the Beech and its allies, 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 some- thing for them- selves. This Fig. 120.—Fossil Leaf 7 with Nests of Infesting Fungal curious, and as Spores / on its lower side yet incompletely understood physiological relation between the higher plants and the fungi, existed so far back as the Paleozoic period, from which roots have been described whose cells were packed with minute organisms apparently identical with M/ycorhzza. Atc&.—Green Aloe (pond weeds). Many impressions have been described as alge from time to time, numbers of which have since been shown to be a variety of other things, sometimes not plants at all. Other impressions may really be those of algz, but hitherto they have added practically nothing to our knowledge of the group. Several genera of alge coat themselves with cal- careous matter while they are alive, much in the same way as do the Charas, and of these, as is natural, there are quite a number of fossil remains from Tertiary and Mesozoic rocks. This is still more the case in the group of the Red Alge (seaweeds), of which the calcareous- 166 ANCIENT PLANTS coated genera, such as Covadiina and others, have many fossil representatives. These plants appear so like corals in many cases that they were long held to be of animal nature. The genus Lzthothamnion now grows attached to rocks, and is thickly encrusted with calcareous matter. A good many species of this genus have been described among: fossils,» particularly from the Tertiary and Cre- taceous rocks, As the plant grew in association with animal corals, it is not always very easy to separate it from them. Brown Aca (seaweeds) have often been described as fossils. This is very natural, as so many fossils have been found in marine deposits, and when among them there is anything showing a dark, wavy impression, it is usually described as a seaweed. And possibly it may be one, but such an impression does not lead to much_ advance in knowledge. From the early Palzozoic rocks of both Europe and America a large fossil plant is known from the partially petrified structure of its stem. There seem to be several species, or at least different varieties of this, known under the generic name Vematophycus. Specimens of this genus are found to have several ana- tomical characters common to the big living seaweeds of the Lamznaria type, and it is very possible that the fossils represent an early member of that group. In none of these petrified specimens, however, is there any indication of the microscopic structure of reproductive organs, so that the exact nature of the fossils is not determinable. It is probable that though perhaps allied to the Laminarias they belong to an entirely extinct group. An interesting and even amusing chapter might be written on all the fossils which look like alge and even have been described as such. The minute river systems. that form in the moist mud of a foreshore, if preserved in the rocks (as they often are, with the ripples and rain- drops of the past), look extraordinarily like seaweeds—as PAST HISTORIES OF PLANT FAMILIES 167 do also countless impressions and trails of animals. In this portion of the study of fossils it is better to have a healthy scepticism than an illuminating imagination. Diatoms, with their hard siliceous shells, are natu- - rally well preserved as fossils (see fig. 121), for even if the protoplasm decays the mineral coats remain practically unchanged. Diatoms to- day exist in great numbers, both in the cold water of the polar regions and in the heat of hot springs. Often, in the latter, one can see them actually being turned into fossils. In the Yellowstone Park they are accumulating in vast num- bers over large areas, and in some places have collected to a thickness of 6 feet. At the . bottoms of freshwater lakes they Fig. 121.—Diatom showing the may form an almost pure mud poe eee urea of fine texture, 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 water. There are enormous numbers of species now living, and of fossils from the Tertiary and Upper Mesozoic rocks; but, strangely enough, though so numerous and so widely distributed, both now and in these past periods, they have not been found in the earlier rocks. In one way the diatoms differ from ordinary fossils. In the latter the soft tissues of the plant have been re- placed by stone, while in the former the living cell was enclosed in a siliceous case which does not decompose, thus resembling more the fossils of animal shells. BACTERIA are so very minute that it is impossible to recognize them in ordinary cases. In the matrix of the best- “preserved fossils are always minute crystals and granules that may simulate bacterial shapes perfectly. Bacillus and Micrococcus of various species have been 168 ANCIENT PLANTS described by French writers, but they do not carry conviction. As was stated at the beginning of the chapter, from all the fossils of all the lower-plant families we cannot learn much of prime importance for the present purpose. Yet, as the history of plants would be incomplete without mention of the little that is known, the foregoing pages have been added. CHAPTER AVHI FOSSIL PLANTS AS RECORDS OF ANCIENT COUNTRIES The land which to-day appears so firm and un- changing has been under the sea many times, and in many different ways has been united to other land masses to form continents. At each period, doubtless, the solid earth appeared as stable as it is now, while the country was as well characterized, and had its typical scenery, plants, and animals. We know what an important feature of the character of any present country is its flora; and we have no reason to suspect that it was ever less so than it is to-day. Indeed, in the ages before men interfered with forest growth, and built their cities, with their destructive influences, the plants were rela- tively more important in the world landscape than they are to-day. As we go back in the periods of geological history we find the plants had an ever-increasing area of dis- tribution. To-day most individual species and many genera are limited to islands or parts of continents, but before the Glacial epoch many were distributed over both America and Europe. In the Mesozoic Gzukgo was spread all over the world, and in the present epoch it was confined to China and Japan till it was distributed FOSSIL PLANTS AS RECORDS 169 again by cultivation; while in the Paleozoic period Lepidodendron seemed to stretch wellnigh from pole to pole. 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 upon. Modern biology and ecology are continually enlarging and render- ing more precise our views of this interrelation, 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 climates. It has been remarked already that most of the fossils which we have well preserved, whether of plants or animals, were fossilized in rocks which collected under sea water; yet it was also noted that of marine plants we have almost no reliable fossils at all. How comes this seeming contradiction? The lack of marine plant fossils probably depends on their easily decomposable nature, while the presence of the numerous land plants resulted from their drifting out to sea in streams and rivers, or dropping into the still salt marshes where they grew. Hence, in the rocks deposited in a sea, we have the plants preserved which grew on adjacent lands. In fresh water, also, the plants of the neighbourhood were often fossilized; but actually on the land itself but little was preserved. The winds and rains and decay that are always at work on a land area tend to break down and wash away its surface, not to build it up. There are many different details which are used in determining the evidence of a fossil plant. Where leaf impressions are preserved which exhibit a close similarity to living species (as often happens in the Tertiary period), it is directly assumed that they lived under conditions like those under which the present plants of that kind are living; while, if the anatomy is well preserved (as in the Paleozoic and several Mesozoic types), we can compare its details with that of similar plants growing 170 ANCIENT PLANTS under known conditions, and judge of the climate that had nurtured the fossil plant while it grew. Previous to the present period there was what is so well known as the Glacial epoch. In the earthy deposits of this age in which fossils are found plants are not un- common: They are of the same kind as those now growing in the cold regions of the Arctic circle, and on the heights of hills whose temperature is much lower than that of the surrounding lowlands. Glacial epochs occurred in other parts of the world at different times; for example, in South Africa, in the Permo-Carboniferous period, during which time the fossils indicate that the warmth-loving plants. were driven much farther north than is now the case. It is largely from the nature of the plant fossils that we know the climate of England at the time preceding the Glacial epoch. Impressions of leaves and stems, and even of fruits, are abundant from the various periods of the Tertiary. Many of them were Angiosperms (see Chap. VIII), and were of the families and even genera which are now living, of which not a few belong to the warm regions of the earth, and are subtropical. It is generally assumed that the fossils related to, or identical with, these plants must therefore have found in Tertiary Northern Europe a much warmer climate than now exists. Not only in Northern Europe, but right up into the Arctic circle, such plants occur in Tertiary rocks, and even if we had not their living representa- tives with which to compare them, the large size and thin texture of their leaves, their smoothness, and a number of other characteristics would make it certain that the climate was very much milder than it is at present, though the value of some of the evidence has been overestimated. From the Tertiary we are dependent chiefly on im- pressions of fossils; anatomical structure would doubtless. yield more details, but even as it is we have quite enough evidence to throw much light on the physio- FOSSIL PLANTS AS RECORDS 17} graphy of the Tertiary period. The causes for such marked changes of climate must be left for the con- sideration of geologists and astronomers. Plants are passive, driven before great climatic changes, though they have a considerable influence on rainfall, as has been proved repeatedly in India in recent times. From the more distant periods it is the plants of the Carboniferous, whose structure we know so well, that teach us most. Although there is still very much to be done before knowledge is as complete as we should wish, there are sufficient facts now discovered to correct several popular illusions concerning the Palzeozoic period. The “deep, all-enveloping mists, through which the sun’s rays could scarcely penetrate”, which have taken the popular imagination, appear to have no foundation in fact. 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-day. | Look at the ‘‘shade leaves” of any ordinary tree, such as a Lime or Maple, and compare them with those growing in the sunlight, even on the same tree. They are larger and softer and thinner. .To absorb the same amount of energy as the more brilliantly lighted leaves, they must expose a larger surface to the light. Hence if the Coal Measure plants grew in very great shade, to supply their large growth with the necessary sun energy we should expect to find enormous spreading leaves. But what is the fact? No such large leaves are known. Cadamites and Lepidodendron, the commonest and most successful plants of the period, had narrow simple leaves with but a small area of surface. They were, in fact, leaves of the type we now find growing in exposed places. The ferns had large divided leaves, but they were finely lobed and did not expose a large continuous area as a true ‘‘shade leaf” does; while the height of their stems indicates that they were grow- ing in partial shade—at least, the shade cast by the 172 ANCIENT PLANTS small-leaved Calamites and Lepidodendrons which ovei- topped them. Indeed there is no indication from geological evi- dence that so late as Paleozoic times there was any great abnormality of atmosphere, and from the internal evidence of the plants then growing there is everything to indicate a dry or physiologically dry? sunny condition. Of the plant fossils from the Coal Measures we have at least two types. One, those commonly found in nodules zz the coal itself; and the other, nodules in the rocks above the coal which had drifted from high lands into the sea. The former are the plants which actually formed the coal itself, and from their internal organization we see that these plants were growing with partly submerged roots in brackish swamps. Their roots are those of water plants (see p. 150, young root of Calamite), but their leaves are those of the “protected” type with narrow surface and various devices for preventing a loss of water by rapid transpiration. If the water they grew in had been fresh they would not have had such leaves, for there would have been no need for them to economize their water, but, as we see in bogs and brackish or salt water to-day (which is physiologically usable in only small quantities by the plant), plants even partly sub- merged protect their exposed leaves from transpiring largely. There are details too numerous to mention in con- nection 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 climate. Extensive areas of coal, and geo- logical evidence of still more extensive deposits, show that in Europe in the Coal Measure period there were vast flats, so near the sea level that they were constantly * A brackish swampy land is physiologically dry, as the plants cannot use the water. See Warming’s Oecology of Plants, English edition, for a detailed account of such conditions. Fora simple account see Stopes’ Zhe Study of Plant Life, p. 170. FOSSIL PLANTS AS RECORDS 173 being submerged and appearing again as débris drifted and collected over them. Such a land area must have differed greatly from the Europe now existing, in all its features. But the whole continent did not consist of these flats; there were hills and higher ground, largely to the north-east, on which a dry land flora grew, a flora where several of the Pteridosperms and Cordaztes with its allies were the principal plants. These plants have leaves so organized as to suggest that they grew in a region where the climate was bright and dry. A fossil flora which has aroused much interest, particularly among geologists, is that known as the Glossopteris flora. This Palzozoic flora has in general characters similar to those of the European Permo- Carboniferous, but it has special features of its own, in particular the genus Gdossopterts and also the genera Phyllotheca and Schizoneura. These genera, with a few others, are characteristic of the Permo-Carboniferous period in the regions in the Southern Hemisphere now known by the names of Aus- tralasia, South Africa, and South America, and in India. These regions, at that date, formed what is called by geologists ‘‘Gondwanaland”. In the rocks below those containing the plants there is evidence of glacial conditions, 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 Hemisphere. Unfortunately we have not microscopically preserved specimens of the Glossopteris flora, which could be compared with those of our own Palzeozoic.* To describe in detail the series of changes through which the seas and continents have passed belongs to the realm of pure geology. Here it is only necessary to point out how the evidence from the fossil plants may afford much information concerning these continents, 1The student interested in this special flora should refer to Arber’s British Museum Catalogue of the Fossil Plants of the Glossopterts Flora. 174 ANCIENT PLANTS and as our knowledge of fossil anatomy and of recent ecology increases, their evidence will become still more weighty. Even now, had we no other sources of in- formation, we could tell from the plants alone where in the past continents were snow and ice, heat and drought, swamps and hilly land. However different in their systematic position or scale of evolutional development, plants have always had similar minute structure and similar physiological response to the conditions of climate and land surface, so that in their petrified cells are pre- served the histories of countries and conditions long past. CHAPTER XIX CONCLUSION In the stupendous pageant of living things which moves through creation, the plants have a place unique and vitally important. Yet so quietly and so slowly do they live and move that we in our hasty motion often forget that they, equally with ourselves, belong to the living and evolving organisms. When we look at the relative structures of plants divided by long intervals of time we can recognize the progress they make; and this is what we do in the study of fossil botany. We can place the salient features of the flora of Paleozoic and Mesozoic eras in a few pages of print, and the con- trast becomes surprising. But the actual distance in time between these two types of plants is immense, and must have extended over several million years; indeed to speak of years becomes meaningless, for the duration of the periods must have been so vast that they pass beyond our mental grasp. In these periods we find a contrast in the characters of the plants as striking as that in the characters of the animals. Whole families died out, and new ones arose of more complex and advanced CONCLUSION 175 organization. But in height and girth there is little difference between the earliest and the latest trees; there seems a limit to the possible size of plants on this planet, as there is to that of animals, the height of mountains, or the depth of the sea. The “higher plants” are often less massive and less in height than the lower—Man is less in stature chan was the Dinosaur—and though by no legitimate stretch of the imagination can we speak of brain in plants, there is an unconscious superiority of adaptation by which the more highly organized plants capture the soil they dominate. 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 present, it was in the reproductive organs that the essential differences lay. Naturally, when a race (as all races do) depends for its very existence on the chain. of individuals leading from generation to generation, the most important items in the plant structures must be those mechanisms concerned with reproduction. It is here that we see the most fundamental differences be- tween living and fossil plants, between the higher and the lower of those now living, between the forest trees of the present and the forest trees of the past. The wood of the palzozoic 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 contrast! The Lycopods, with simple cones composed of scales in whose huge sporangia were simple single-celled spores; the flowering plants, with male and female sharply contrasted yet grow- ing in the same cone (one can legitimately compare a flower with a cone), surrounded by specially coloured and protective scales, and with the “spore” in the tissue of the young seed so modified and changed that it is only in a technical sense that comparison with the Lyco- pod spore is possible. To study the minute details of fossil plants it is 176! ANCIENT PLANTS necessary to have an elaborate training in the structure of living ones. In the preceding chapters only the salient features have been considered, 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 lines. Even from the facts brought together in these short chapters, however, it cannot fail to be evident how large a field fossil botany covers, and with how many subjects it comes in touch. From the minute details of plant anatomy and evolution pure and simple to the climate of departed continents, 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 ques- tions of the preservative properties of sea water, all is a part of the study of “fossil botany ”. To bring together the main results of the study in a graphic form is not an easy task, 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 (see fig. 122). Such a diagram can only represent the present state of our imperfect knowledge; any day discoveries may extend the line of any group up or down in the series, or may connect the groups together. It becomes evident that so early as the Palzozoic there are nearly as many types represented as in the present day, and that in fact everything, up to the higher Gymnosperms, was well developed (for it is hard indeed to prove that Cordaztes is less highly organized than some of the present Gymnosperm types), but flowering plants and also the true cycads are wanting, as well as the intermediate Mesozoic Bennettitales. The peculiar groups of the period were the Pterido- sperm series, connecting links between fern and cycad, and the Sphenophyllums, connecting in some measure the Lycopods and Calamites. 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