Paleobotany

“ That which chiefly distinguished the Palæozoic from the Secondary and Tertiary periods was its gorgeous flora. It was emphatically the period of plants,—"of herbs yielding seed after their kind." In no other age did the world ever witness such a flora: the youth of the earth was peculiarly a green and umbrageous youth,—a youth of dusk and tangled forests, of huge pines and stately araucarians, of the reed-like calamite, the tall tree-fern, the sculptured sigillaria, and the hirsute lepidodendron. ”

“ It is impossible to follow in the case of all fossil species precisely the same treatment as with the more complete and perfect recent plants; but it is of the utmost importance for a student of palaeobotany, by adhering to the methods of recent botany, to preserve as far as he is able the continuity of the past and present floras. ”

“ It may be premised that the modes of determination in fossil botany are necessarily different from those employed in recent botany. The palæobotanist must have recourse to characters derived from the leaves, the scars left by their fall, and the internal structures of the stem. These parts, held in little esteem by botanists in describing modern plants, and much neglected by them, must hold the first place in the regard of the fossil botanist, whereas the fructification, seldom preserved, and generally obscure, is of comparatively little service. ”

“ From many parts of the world large collections of fossil plants have been obtained from strata referred to the Rhaetic period, or to the upper division of the Triassic system. A comparison of floras from these geological horizons in different parts of the world points to a vegetation extending from Australia, Cape Colony, and South America, to Tonkin, the south of Sweden and North America, which was characterised by a greater uniformity than is shown by widely separated floras at the present day. ”

“ In the early part of the present century, and still more in the eighteenth century, the occurrence of fossil plants and animals in the earth’s crust formed the subject of animated, not to say acrimonious, discussion. The result was that many striking and ingenious theories were formulated as to the exact manner of formation of fossil remains, and the part played by the waters of the deluge in depositing fossiliferous strata. The earlier views on fossil vegetables are naturally bound up with the gradual evolution of geological science. ”

“ It would, from this point of view, be a nice question to calculate how many revolutions of climate would suffice to evolve the first land-plant; what are the chances that such plant would be so dealt with by physical changes as to be preserved and nursed into a meagre flora like that of the Upper Silurian or the Jurassic; how many transportations to Greenland would suffice to promote such meagre flora into the rich and abundant forests of the Upper Cretaceous, and to people the earth with the exuberant vegetation of the early Tertiary. Such problems we may never be able to solve. ”

“ The study of fossil animals embraces a much greater range of subject than that of fossil plants. The fauna of any particular geological formation, that is to say, its embedded animal remains, for the most part vastly exceeds in number its flora, or vegetable remains, and is likewise usually better preserved. About the nature and affinities of several tribes of fossil plants there hangs an amount of uncertainty which renders them a dubious guide to the climatal and other conditions of the period and locality in which they lived. ”

“ Antiquity of Plants as affecting their Distribution.—We have already referred to the importance of great antiquity in enabling us to account for the wide dispersal of some genera and species of insects and land-shells, and recent discoveries in fossil botany show that this cause has also had great influence in the case of plants. Rich floras have been discovered in the Miocene, the Eocene, and the Upper Cretaceous formations, and these consist almost wholly of living genera, and many of them of species very closely allied to existing forms. ”

“ But let us suppose that no fruit, seed, or flower had ever been met with in a fossil state, we should still have been indebted to the persevering labours of botanical palæontologists for one of the grandest scientific discoveries for which the present century is remarkable—namely, the proofs now established of the prevalence of a mild climate and a rich arborescent flora in the arctic regions in that Miocene epoch on the history of which we are now entering. ”

“ While always on the alert for rational explanations of obscure phenomena by means of the analogy supplied by existing causes, and ready to draw from a wide knowledge of recent botany, in the interpretation of problems furnished by fossil plants, the palaeobotanist must be constantly alive to the necessity for cautious statement. That there is the greatest need of moderation and safe reasoning in dealing with the botanical problems of past ages, will be apparent to anyone possessing but a superficial acquaintance with fossil plant literature. ”

“ The distribution of fossil plants lies at the foundation of the principles of the present grouping of floras on the Earth’s surface. Those who have confined their study of distribution to the plant geography of the present age, must supplement their investigations by reference to the work of palaeobotanical writers. If the lists of plant species drawn up by specialists in fossil botany, have been prepared with a due sense of the important conclusions which botanists may draw from them from the standpoint of distribution, they will be readily accepted as sound links in the chain of evidence. ”

“ Of the accumulated remains of these plants coal seams are really composed, and one cause of the differences amongst them is the different structural composition of the original plants. How far the above fossil flora is to be taken as exhibiting the true proportions of the tribes of plants living on the globe, at the time of the production of the rocks of the carboniferous system, is uncertain: since, when plants are swept down from the land into the sea, it depends on many unknown conditions what sorts of them shall escape the floods, or perish by maceration in the waters. ”

“ Concurrently with this change, the tropical and extinct forms disappeared, and the flora approached more and more nearly to that now existing in the districts where the fossil plants are found, though in the older deposits, at any rate, the geographical distribution still differed considerably from that now met with. At last, in the latest Pliocene strata (often called “pre-Glacial”) we find a flora consisting almost entirely of existing species belonging to the Palaearctic regions, and nearly all still living in the country where the fossils are found. ”

“ Instead of the few small specimens of tropical vegetation now preserved in our museums, I hope that hereafter, in every school where geology and palæontology are taught, we shall have large stems and portions of trunks to show the structure of palms, tree-ferns, and the like,—trees which represent in modern times the ancient geological forests. The time is coming when our text-books of botany and zoölogy will lose their local, limited character, and present comprehensive pictures of Nature in all her phases. ”

“ For our present purpose it is, however, enough to know that the members of the sub-Kingdom of the Angiosperms, or Flowering Plants, are not only the most recent in point of evolution, but the most numerous in the vegetable world of to-day. They embrace an endless variety of species widely different, in form, size and structural complexity. They exist under all the conditions of life, from the dense jungle of the Tropics to the home of eternal snows. In the ordinary walks of life we meet them everywhere, dominating our woodlands, prairies, meadows and ponds. ”

“ When the story resumes again, we find life entering upon a fresh phase of richness and expansion. Vegetation has made great advances in the art of living out of water. While the Palæozoic plants of the coal-measures probably grew with swamp water flowing over their roots, the Mesozoic flora from its very outset included palm-like cycads and low-ground conifers that were distinctly land plants growing on soil above the water level. The lower levels of the Mesozoic land were no doubt covered by great fern brakes and shrubby bush and a kind of jungle growth of trees. ”

“ They consist of blue clays with some subordinate layers of lignite, and exhibit a richer flora than the overlying Newer Pliocene beds, and one receding farther from the existing vegetation of Europe. They also comprise more species common to the antecedent Miocene period. Among the genera of flowering plants, M. Gaudin enumerates pine, oak, evergreen oak, plum, plane, alder, elm, fig, laurel, maple, walnut, birch, buckthorn, hickory, sumach, sarsaparilla, sassafras, cinnamon, Glyptostrobus, Taxodium, Sequoia, Persea, Oreodaphne (Fig. 134) , Cassia, and Psoralea, and some others. ”

“ They afford the first positive proof as yet obtained of the co-existence of a varied fauna of the highest class of vertebrata with that ample development of reptile life which marks all the periods from the Trias to the Lower Cretaceous inclusive, and with a gymnospermous flora, or that state of the vegetable kingdom when cycads and conifers predominated over all kinds of plants, except the ferns, so far, at least, as our present imperfect knowledge of fossil botany entitles us to speak. ”

“ It needs but a slight acquaintance with Geology for a Botanist to estimate the value of the most important applications of Palaeobotany; on the other hand, the bearing of fossil plants on the problems of phylogeny andvi descent cannot be adequately understood without a fairly intimate knowledge of recent Botany.
The student of elementary geology is not as a rule required to concern himself with vegetable palaeontology, beyond a general acquaintance with such facts as are to be found in geological text-books. ”

“ Applying the knowledge gained from living plants to the study of such extinct types as permit of close microscopic examination, we may obtain a glimpse into the secrets of the botanical binomics of Palaeozoic times. The wider questions of climatic conditions depend very largely upon the evidence of fossil botany for a rational solution. ”

“ Comparative number of living and fossilized species of plants.—It will appear from these observations that, although the remains of terrestrial vegetation, borne down by aqueous causes from the land, are chiefly deposited at the bottom of lakes or at the mouths of rivers, yet a considerable quantity is drifted about in all directions by currents, and may become imbedded in any marine formation, or may sink down, when water-logged, to the bottom of unfathomable abysses, and there accumulate without intermixture with other substances. ”

“ The transportation of seeds of plants by water requires very little notice; every one is familiar with the mode in which coral islands, which gradually rise out of the sea, become covered with vegetation. "If new lands are formed, the organic forces are ever ready to cover the naked rock with life.—Lichens form the first covering of the barren {75}rocks, where afterwards lofty forest trees wave their airy summits. The successive growth of mosses, grasses, herbaceous plants and shrubs or bushes, occupies the intervening period of long but undetermined duration." ”

“ Plants have pursued their migrations under the rule of this phenomenon, moving toward the south and gradually abandoning the north, beginning with the extreme north, or the immediate environs of the pole. The discovery of numerous vegetable fossils at different points in the arctic regions, in Spitzbergen, Greenland, Grinnell Land, etc., has been sufficient to give rise to terms of comparison and demonstrate what was the character of fossil vegetation when that of Europe more or less resembled the present vegetation of countries near the tropics. ”

“ From the fossil remains of each, and their position in the crust of the earth, it is well ascertained, that their genera were created successively, and that the most ancient genera are extinct. The same is true in regard to vegetables. It is equally true, that, connected with the successive creation, was a successive improvement in the delicacy and complexity of their structure and parts. There was also a reduction in the size of fishes, and quadrupeds, and a great reduction in the amount of vegetation, as well as the size of many of the plants. ”

“ American Character of the Flora.—If we consider not merely the number of species but those plants which constitute the mass of the Lower Miocene vegetation, we find the European part of the fossil flora very much less prominent than in the Œningen beds, while the foreground is occupied by American forms, by evergreen oaks, maples, poplars, planes, Liquidambar, Robinia, Sequoia, Taxodium, and ternate-leaved pines. ”

“ The connexion between climate and vegetation has also been studied. Quite recently under the name of “Ecology” or “Oecology” the study of plants in relation to each other and to their environment has become the subject of systematic investigation.
The subject of palaeontological botany (see Palaeobotany) has been advanced by the researches of both botanists and geologists. The nature of the climate at different epochs of the earth’s history has also been determined from the character of the flora. ”