CHAPTER I.
HISTORICAL SKETCH.
“But particular care ought to be had not to consult or take relations from any but those who appear to have been both long conversant in these affairs, and likewise persons of Sobriety, Faithfulness and Discretion, to avoid the being misled and imposed upon either by falsehood, or the ignorance, credulity, and fancifulness, that some of these people are but too obnoxious unto.” John Woodward, 1728.
The scientific study of fossil plants dates from a comparatively recent period, and palaeobotany has only attained a real importance in the eyes of botanists and geologists during the last few decades of the present century. It would be out of place, in a short treatise like the present, to attempt a detailed historical sketch, or to give an adequate account of the gradual rise and development of this modern science. An excellent Sketch of Palaeobotany has recently been drawn up by Prof. Lester Ward[1], of the United States Geological Survey, and an earlier historical retrospect may be found in the introduction to an important work by an eminent German palaeobotanist, the late Prof. Göppert[2]. In the well-known work by Parkinson on The Organic Remains of a Former World[3] there is much interesting information as to the early history of our knowledge of fossil plants, as well as a good exposition of the views held at the beginning of this century.
FOSSIL PLANTS AND THE FLOOD.
As a means of bringing into relief the modern development of the science of fossil plants, we may briefly pass in review some of the earlier writers, who have concerned themselves in a greater or less degree with a descriptive or speculative treatment of the records of a past vegetation. 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 is from Italy that we seem to have the first glimmering of scientific views; but we are led to forget this early development of more than three hundred years ago, when we turn to the writings of English and other authors of the eighteenth century. “Under these white banks by the roadside,” as a writer on Verona has expressed it, “was born, like a poor Italian gipsy, the modern science of geology.” Early in the sixteenth century the genius of Leonardo da Vinci[4] compelled him to adopt a reasonable explanation of the occurrence of fossil shells in rocks far above the present sea-level. Another Italian writer, Fracastaro, whose attention was directed to this matter by the discovery of numerous shells brought to light by excavations at Verona, expressed his belief in the organic nature of the remains, and went so far as to call in question the Mosaic deluge as a satisfactory explanation of the deposition of fossil-bearing strata.
The partial recognition by some observers of the true nature of fossils marks the starting point of more rational views. The admission that fossils were not mere sports of nature, or the result of some wonderful ‘vis lapidifica,’ was naturally followed by numerous speculations as to the manner in which the remains of animals and plants came to be embedded in rocks above the sea-level. For a long time, the ‘universal flood’ was held responsible by nearly all writers for the existence of fossils in ancient sediments. Dr John Woodward, in his Essay toward a Natural History of the Earth, propounded the somewhat revolutionary theory, that “the whole terrestrial globe was taken all to pieces and dissolved at the Deluge, the particles of stone, marble, and all solid fossils dissevered, taken up into the water, and there sustained together with sea-shells and other animal and vegetable bodies: and that the present earth consists, and was formed out of that promiscuous mass of sand, earth, shells, and the rest falling down again, and subsiding from the water[5].” In common with other writers, he endeavoured to fix the exact date of the flood by means of fossil plants. Speaking of some hazel-nuts, which were found in a Cheshire moss pit, he draws attention to their unripened condition, and adds: “The deluge came forth at the end of May, when nuts are not ripe.” As additional evidence, he cites the occurrence of “Pine cones in their vernal state,” and of some Coal-Measure fossils which he compares with Virginian Maize, “tender, young, vernal, and not ripened[6].” Woodward (1665–1728) was Professor of Physic in Gresham College; he bequeathed his geological collections to the University of Cambridge, and founded the Chair which bears his name.
Another writer, Mendes da Costa, in a paper in the Philosophical Transactions for 1758, speaks of the impressions of “ferns and reed-like plants” in the coal-beds, and describes some fossils (Sigillaria and Stigmaria) as probably unknown forms of plant life[7].
Here we have the suggestion that in former ages there were plants which differed from those of the present age. Discussing the nature of some cones (Lepidostrobi) from the ironstone of Coalbrookdale in Shropshire, he concludes: “I firmly believe these bodies to be of vegetable origin, buried in the strata of the Earth at the time of the universal deluge recorded by Moses.” Scheuchzer of Zurich, the author of one of the earliest works on fossil plants and a “great apostle of the Flood Theory,” figures and describes a specimen as an ear of corn, and refers to its size and general appearance as pointing to the month of May as the time of the deluge[8]. Another English writer, Dr Parsons, in giving an account of the well-known ‘fossil fruits and other bodies found in the island of Sheppey,’ is disposed to dissent from Woodward’s views as to the time of the flood. He suggests that the fact of the Sheppey fruits being found in a perfectly ripe condition, points to the autumn as the more probable time for the occurrence of the deluge[9].
In looking through the works of the older writers, and occasionally in the pages of latter-day contributors, we frequently find curiously shaped stones, mineral markings on rock surfaces, or certain fossil animals, described as fossil plants. In Plot’s Natural History of Oxfordshire, published in 1705, a peculiarly shaped stone, probably a flint, is spoken of as one of the ‘Fungi lethales non esculenti[10]’; and again a piece of coral[11] is compared with a ‘Bryony root broken off transversely.’ On the other hand, that we may not undervalue the painstaking and laborious efforts of those who helped to lay the foundations of modern science, we may note that such authors as Scheuchzer and Woodward were not misled by the moss-like or dendritic markings of oxide of manganese on the surface of rocks, which are not infrequently seen to-day in the cabinets of amateurs as specimens of fossil plants.
The oldest figures of fossil plants from English rocks which are drawn with any degree of accuracy are those of Coal-Measure ferns and other plants in an important work by Edward Lhwyd published at Oxford in 1760[12].
Passing beyond these prescientific speculations, brief reference may be made to some of the more eminent pioneers of palaeobotany. The Englishman Artis[13] deserves mention for the quality rather than the quantity of his contributions to Palaeozoic botany; and among American authors Steinhauer’s[14] name must hold a prominent place in the list of those who helped to found this branch of palaeontology. Among German writers, Schlotheim stands out prominently as one who first published a work on fossil plants which still remains an important book of reference. Writing in 1804, he draws attention to the neglect of fossils from a scientific standpoint; they are simply looked upon, he says, as “unimpeachable documents of the flood[15].” His book contains excellent figures of many Coal-Measure plants, and we find in its pages occasional comparisons of fossil species with recent plants of tropical latitudes. Among the earlier authors whose writings soon become familiar to the student of fossil plants, reference must be made to Graf Sternberg, who was born three years before Schlotheim, but whose work came out some years later than that of the latter. His great contribution to Fossil Botany entitled Versuch einer geognostisch-botanischen Darstellung der Flora der Vorwelt, was published in several parts between the years 1820 and 1838; it was drawn up with the help of the botanist Presl, and included a valuable contribution by Corda[16]. In addition to descriptions and numerous figures of plants from several geological horizons, this important work includes discussions on the formation of coal, with observations on the climates of past ages.
STERNBERG AND BRONGNIART.
Sternberg endeavoured to apply to fossil plants the same methods of treatment as those made use of in the case of recent species. About the same time as Sternberg’s earlier parts were published, Adolphe Brongniart[17] of Paris began to enrich palaeobotanical science by those splendid researches which have won for him the title of the “Father of palaeobotany.” In Brongniart’s Prodrome, and Histoire des végétaux fossiles, and later in his Tableau des genres de végétaux fossiles, we have not merely careful descriptions and a systematic arrangement of the known species of fossil plants, but a masterly scientific treatise on palaeobotany in its various aspects, which has to a large extent formed the model for the best subsequent works on similar lines. From the same author, at a later date, there is at least one contribution to fossil plant literature which must receive a passing notice even in this short sketch. In 1839 he published an exhaustive account of the minute structure of one of the well-known Palaeozoic genera, Sigillaria; this is not only one of the best of the earliest monographs on the histology of fossil species, but it is one of the few existing accounts of the internal structure of this common type[18]. The fragment of a Sigillarian stem which formed the subject of Brongniart’s memoir is in the Natural History Museum in the Jardin des Plantes, Paris. It affords a striking example of the perfection of preservation as well as of the great beauty of the silicified specimens from Autun, in Central France. Brongniart was not only a remarkably gifted investigator, whose labours extend over a period connecting the older and more crude methods of descriptive treatment with the modern development of microscopic analysis, but he possessed the power of inspiring a younger generation with a determination to keep up the high standard of the palaeobotanical achievements of the French School. In some cases, indeed, his disciples have allowed a natural reverence for the Master to warp their scientific judgement, where our more complete knowledge has naturally led to the correction of some of Brongniart’s conclusions. Without attempting to follow the history of the science to more recent times, the names of Heer, Lesquereux, Zigno, Massalongo, Saporta and Ettingshausen should be included among those who rendered signal service to the science of fossil plants. The two Swiss writers, Heer[19] and Lesquereux[20], contributed numerous books and papers on palaeobotanical subjects, the former being especially well known in connection with the fossil floras of Switzerland and of Arctic lands, and the latter for his valuable writings on the fossil plants of his adopted country, North America. Zigno[21] and Massalongo[22] performed like services for Italy, and the Marquis of Saporta’s name will always hold an honourable and prominent position in the list of the pioneers of scientific palaeobotany; his work on the Tertiary and Mesozoic floras of France being specially noteworthy among the able investigations which we owe to his ability and enthusiasm[23]. In Baron Ettingshausen[24] we have another representative of those students of ancient vegetation who have done so much towards establishing the science of fossil plants on a philosophical basis.
As in other fields of Natural Science, so also in a marked degree in fossil botany, a new stimulus was given to scientific inquiry by the application of the microscope to palaeobotanical investigation. In 1828 Sprengel published a work entitled Commentatio de Psarolithis, ligni fossilis genere[25]; in which he dealt in some detail with the well-known silicified fern-stems of Palaeozoic age, from Saxony, basing his descriptions on the characteristics of anatomical structure revealed by microscopic examination.
THE INTERNAL STRUCTURE OF FOSSIL PLANTS.
In 1833 Henry Witham of Lartington brought out a work on The Internal Structure of Fossil Vegetables[26]; this book, following the much smaller and less important work by Sprengel, at once established palaeobotany on a firmer scientific basis, and formed the starting point for those more accurate methods of research, which have yielded such astonishing results in the hands of modern workers. In the introduction Witham writes, “My principal object in presenting this work to the public, is to impress upon geologists the advantage of attending more particularly to the intimate organization of fossil plants; and should I succeed in directing their efforts towards the elucidation of this obscure subject, I shall feel a degree of satisfaction which will amply repay my labour[27].”
On another page he writes as follows,—“From investigations made by the most active and experienced botanical geologists, we find reason to conclude that the first appearance of an extensive vegetation occurred in the Carboniferous series; and from a recent examination of the mountain-limestone groups and coal-fields of Scotland, and the north of England, we learn that these early vegetable productions, so far from being simple in their structure, as had been supposed, are as complicated as the phanerogamic plants of the present day. This discovery necessarily tends to destroy the once favourite idea, that, from the oldest to the most recent strata, there has been a progressive development of vegetable and animal forms, from the simplest to the most complex[28].” Since Witham’s day we have learnt much as to the morphology of Palaeozoic plants, and can well understand the opinions to which he thus gives expression.
It would be difficult to overrate the immense importance of this publication from the point of view of modern palaeobotany.
The art of making transparent sections of the tissues of fossil plants seems to have been first employed by Sanderson, a lapidary, and it was afterwards considerably improved by Nicol[29]. This most important advance in methods of examination gave a new impetus to the subject, but it is somewhat remarkable that the possibilities of the microscopical investigation of fossil plants have been but very imperfectly realised by botanical workers until quite recent years. As regards such a flora as that of the Coal-Measures, we can endorse the opinion expressed at the beginning of the century in reference to the study of recent mosses—“Ohne das Göttergeschenk des zusammengesetzten Mikroskops ist auf diesem Felde durchaus keine Ernte[30].” A useful summary of the history of the study of internal structure is given by Knowlton in a memoir published in 1889[31]. Not long after Witham’s book was issued there appeared a work of exceptional merit by Corda[32], in which numerous Palaeozoic plants are figured and fully described, mainly from the standpoint of internal structure. This author lays special stress on the importance of studying the microscopical structure of fossil plants.
ENGLISH PALAEOBOTANISTS.
Without pausing to enumerate the contributions of such well-known continental authors as Göppert, Cotta, Schimper, Stenzel, Schenk and a host of others, we may glance for a moment at the services rendered by English investigators to the study of palaeobotanical histology. Unfortunately we cannot always extend our examination of fossil plants beyond the characters of external form and surface markings; but in a few districts there are preserved remnants of ancient floras in which fragments of stems, roots, leaves and other structures have been petrified in such a manner as to retain with wonderful completeness the minute structure of their internal tissues. During the deposition of the coal seams in parts of Yorkshire and Lancashire the conditions of fossilisation were exceptionally favourable, and thus English investigators have been fortunately placed for conducting researches on the minute anatomy of the Coal-Measure plants. The late Mr Binney of Manchester did excellent service by his work on the internal structure of some of the trees of the Coal Period forests. In his introductory remarks to a monograph on the genus Calamites, after speaking of the desirability of describing our English specimens, he goes on to say, “When this is done, we are likely to possess a literature on our Carboniferous fossils worthy of the first coal-producing country[33].” The continuation and extension of Binney’s work in the hands of Carruthers, Williamson, and others, whose botanical qualifications enabled them to produce work of greater scientific value, has gone far towards the fulfilment of Binney’s prophecy.
DIFFICULTIES OF IDENTIFICATION.
In dealing with the structure of Palaeozoic plants, we shall be under constant obligation to the splendid series of memoirs from the pen of Prof. Williamson[34]. As the writer of a sympathetic obituary notice has well said: “In his fifty-fifth year he began the great series of memoirs which mark the culminating point of his scientific activity, and which will assure to him, for all time, in conjunction with Brongniart, the honourable title of a founder of modern Palaeobotany[35].” If we look back through a few decades, and peruse the pages of Lindley and Hutton’s classic work[36] on the Fossil flora of Great Britain, a book which is indispensable to fossil botanists, and read the description of such a genus as Sigillaria or Stigmaria; or if we extend our retrospect to an earlier period and read Woodward’s description of an unusually good specimen of a Lepidodendron, and finally take stock of our present knowledge of such plants, we realise what enormous progress has been made in palaeobotanical studies. Lindley and Hutton, in the preface to the first volume of the Flora, claim to have demonstrated that both Sigillaria and Stigmaria were plants with “the highest degree of organization, such as Cactaeae, or Euphorbiaceae, or even Asclepiadeae”; Woodward describes his Lepidodendron (Fig. 1) as “an ironstone, black and flat, and wrought over one surface very finely, with a strange cancellated work[37].” Thanks largely to the work of Binney, Carruthers, Hooker, Williamson, and to the labours of continental botanists, we are at present almost as familiar with Lepidodendron and several other Coal-Measure genera as with the structure of a recent forest tree. While emphasizing the value of the microscopic methods of investigation, we are not disposed to take such a hopeless view of the possibilities of the determination of fossil forms, in which no internal structure is preserved, as some writers have expressed. The preservation of minute structure is to be greatly desired from the point of view of the modern palaeobotanist, but he must recognise the necessity of making such use as he can of the numberless examples of plants of all ages, which occur only in the form of structureless casts or impressions.
Fig. 1. Four leaf-cushions of a Lepidodendron. Drawn from a specimen in the Woodward Collection, Cambridge. (Nat. size.)
In looking through the writings of the earlier authors we cannot help noticing their anxiety to match all fossil plants with living species; but by degrees it was discovered that fossils are frequently the fragmentary samples of extinct types, which can be studied only under very unfavourable conditions. In the absence of those characters on which the student of living plants relies as guides to classification, it is usually impossible to arrive at any trustworthy conclusions as to precise botanical affinity. Brongniart and other authors recognised this fact, and instituted several convenient generic terms of a purely artificial and provisional nature, which are still in general use. The dangers and risks of error which necessarily attend our attempts to determine small and imperfect fragments of extinct species of plants, will be briefly touched on in another place.