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    "title": "PALAEOBOTANY",
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    "verified_text": "palaeobotany or the science of the study of fossil plants has three main aspects, dependent on the nature of the remains available for study. (1) external impressions and casts of plants, such as fern leaves found in shale beds, for instance, which are given specific names and often are of value in connection with stratigraphy and the sequence of the extinct floras of various geological epochs. ii the identification and correlation of these fragments is essen- tially an international work, and depends on a wide knowledge of the type specimens in all countries. (2) petrifications of the inner detail and cellular anatomy of fossil plants, such as stems, seeds, etc., found principally pre- served in silicified or calcified mineral balls or nodules, primarily of botanical interest in revealing the structure and life histories of extinct types. the originators of the meticulous kind of in- vestigation they require were principally the french, english and german palacobotanists of last century, though now pet- rified remains are being discovered and investigated in many countries. (3) the peculiarly preserved ‘“ mummified ” masses of plant material known as coal of whatever geological age, the exact nature and detailed structure of which has long been the sub- ject of speculation. in spite of its huge commercial importance, it has received but scant investigation on truly scientific lines. collaboration between palaeobotanists and chemists as well as geologists, is yielding a mass of new data, principally about british and american coals (see coal). relations with anatomical botany.—progress in palaeobotany essentially goes hand in hand with that in anatomical botany, each stimulating and filling in the gaps in the other, and it is more and more becoming impossible to discuss the anatomy or the phylogeny of the great groups of living plants without ref- erence to their fossil ancestors. 7 angiosperms.—the angiosperms, the greatest of all living groups, have principally yielded plant ‘ impressions ” rather than anatomical material. these are common in a number of tertiary and upper cretaceous horizons, and voluminous mem- oirs have been published on them in recent years, principally by e. w. berry of america. the dakota sandstones have yielded perhaps the handsomest series of large angiospermic leaf impressions in the world. from the united states also emanated substantial work on the angiospermic leaf impres- sions of the west indies by hollick (1924). a memoir from china, published at peking (1922), is r. florin’s account of the plant impressions of early tertiary age of manchuria. upper cretaceous angiosperms were described by stopes and fujii from japan, among which is the earliest known petrified flower. this is of monocotyledonous type. tertiary materital——in england, the rich deposits of tertiary material, so long neglected, have been partly investigated by the newer methods which yield microscopic data about the cuticles, by h. bandulska (1923-4). similarly r. krausel had investigated tertiary impressions, discovering many interesting microscopic fungi upon the remains. the arctic floras were revised (1925) in a jubilee memoir by seward. whether the monocotyledons or the dicotyledons are the more primitive is not settled by the fossil record. with the exception of palms, fossil monocotyledons are very few. many discussions have raged about the evidence afforded by the angiospermic fossil floras on ancient climates, particularly centring around dr. knowlton of america. a greater regional diversity, and less world-wide similarity of climate over long epochs than was for- merly assumed, may be taken to be the main result of closer investigation (see climate). the origin and phylogenetic source of the angiosperms is still a mystery. authenticated leaf impressions do not go very far back, and petrified angiosperms are exceedingly scarce in the earlier cretaceous deposits, and unknown before that. in spite of various identifications, no reliable material of modern angio- spermic type has been found as early as the wealden in britain or approximately the neocomian in any part of the world. im- pressions claimed to be such have proved to be portions of fern leaves with reticulate venation, such as dictyophyllum (berry and stopes). the earliest authentic angiosperms in the world are from the lower greensand or aptian, of england. this flora is of a rich mixed type, is markedly distinct in other ways, and con- tains the famous bennettites gibsonianus of carruthers, and many conifers as well as ferns. the angiosperms, discovered by 12 stopes, are well petrified portions of secondary woods, and are of 5 genera, named cantia, woburnia, sabulia, aptiana and hythia. they are unlike each other anatomically, one having enormous wood vessels, and another very minute, nor do they show any “ primitive ” or pseudo-angiospermic features. they have the characteristics of highly organised angiospermic sec- ondary timbers. the origin of the angiosperms clearly lies in an earlier geo- logical epoch. jeffrey and his american school have enunciated the view that the soft small herbaceous plants now living are less primitive than the woody trees. the matter still awaits further data from actual species of an early geological age. interest in such theoretical discussions has been greatly en- hanced by the discovery and description by ii. ii. thomas of his jurassic genus caytonia. gymitos perms.—gymnosperms, of tree-like build, date back to very early palaeozoic times, and are represented by a rich variety of material, including external casts, ‘‘ mummified ” cuticles and well-petrifed woods. a steady stream of memoirs dealing with the comparative anatomy of fossil and living gymnosperms has been maintained. | petrified remains of numerous genera of the modern coniferae are found throughout the tertiary and mesozoic horizons. whether the abietineae or araucarineae are the older stock is much discussed. the latest edition of scott’s classic textbook (1923) leaves the subject still open. the ancient gymnospermic types of the cordaiteae were most abundant and varied in the carboniferous epoch, but persisted into the permian and were already well established in the upper devonian. anatomically preserved stems and leaves yield some of the most beauti- fully petrified and satisfactory material for microscopic study. notable carly representatives of this group were found at the very base of the carboniferous of kentucky and described by scott and jeffrey. various species form series of almost con- necting links between this palaeozoic group and the typical pteridospermic types. very full descriptions of those interesting seed plants are to be found in scoit’s “ studies.” returning to the higher group, the bennettitales, we have to deal with another entirely extinct, but pre-eminently mesozoic family. a few stragglers died out in the early tertiary, but the rich growths preserved in such perfection and abundance which proved the basis of the discoveries of carruthers, wieland, lig- nier and stopes, all date from the mesozoic. wieland’s two magnificent volumes (1916) contain restorations of these unique plants which have served as the theme of countless discussions. the fructifications, preserved both as surface casts and as pet- rified cones, even containing the tissues of the embryos, con- sisted of seed-bearing cones surrounded by pcrianth-like bracts. the mass of seeds contained in some of those must have been enormous, ¢.g., b. albianus, stopes, from the english gault, had not less than several thousand seeds in one cone. though the external appearance and vegetative anatomy of the group were generally like those of the living cycads, the fructification irresistibly recalls that of the angiosperms, and many authors have compared them and concluded that the bennettitales point out the line of descent of the angiosperms. this view does not gencrally commend itself. the other great mesozoic group, the [willtamsoniaceae, chiefly known through nathorst’s work on swedish forms, and more recently by thomas’s beautiful species from the english jurassic, seems to be a more popular candidate for the honour of fathering the angiosperms. the series linked up by wifliamsoniclla, caytonia and gristhorpia is one of the most beautiful results of recent palaeobotanical work; but their angiospermic afhnity is more critically treated on the continent than in england, particu- larly by gothan in germany. the abundance of the bennetti- tales in europe and america makes the dearth of the group in asia conspicuous, and interest thus attaches to the brief account of a trunk from hokkaido, japan, by a. kryshtovovich. cycadales—the modern cycadales, though primitive among living plants, are unimportant in the fossil record, which con- tains but little evidence of their history. palaeobotany ptertdosperms.—the pteridosperms, a wholly extinct group, bulk largely both in actual number of specimens and in the in- terest and importance of their structure in the carboniferous epoch. to impressions of their foliage, long considered true ferns, numerous generic names have been given, such as sphen- opterts, alethopteris, etc. the stems and seeds investigated prin- cipally by williamson, scott, oliver and kidston were, just before 1910, all linked in association with each other to form the phylogenetically pregnant group of the “‘ seed ferns ” or pteri- dosperms. much detail has since been added, which is well sum- marised in scott's ‘* studies.” pteridophytes.—the pteridophytes, or ferns proper, are ex- tensively represented in all types of preservation in all geological epochs. considerable detail has been added to the existing knowledge of the group since 1915. anatomical data have been chiefly acquired about carboniferous species. of families with living representatives the most important extensions of knowl- edge have been made in the osmundaceae in which family kid- ston and gwynne-vaughan (1914) have been the most notable in filling in anatomical series for a wide range of geological time. the afarratiaceue-—these are represented in the coal meas- ures and permian by the large and well preserved genus psar- onius, has long been well known, but knowledge was usefully clarified and increased by p. bertrand in his paper on the anat- omy of ancient ferns and count solms-laubach on psaronius (both in rg11) followed by pelourde in ror2. tempskya, an extinct type of peculiar anatomical structure and wide geological distribution, was at last made clear by the work of kidston and gwynne-vaughan. access to their original paper, published in russia, is difficult and reference should be mace to stopes (1915) and seward (1924). the extinct family of the botryopterideae, the most extensive carboniferous family, is represented by many genera known from exceptionally de- tailed studies of excellent petrifactions, particularly by ber- trand, scott, kidston and gordon. the sporangia and cuticle structures of many species of ferns have also been studied by the modern methods of treating mummified remains, and results from the palaeozoic and mesozoic supplement and give signifi- cance to the work of bower on recent ferns. lower pteridophyta.—of the lycopodineae almost the whole of our present anatomical knowledge was accumulated before roro. the same applies to the calamaricae, with the exception of thomas’s paper on the leaves in 1911 and the elaborate memoir on the calamites of western europe by kidston and jongmans. in the more primitive groups, active interest was shown by halle in the devonian flora from norway. he described the external morphology and some structural details of a number of species which have proved of the greatest morphological signifi- cance. kidston and lang followed with details of the devonian flora contained in the now famous rhynia cherts. psilophyion.—this has now become of peculiar interest since rhynia has been discovered in plentiful anatomical matcrial. this and other devonian genera have been described by kidston and lang in several large memoirs, and a new class, the psilo- phytales, has been instituted to include psilophyton, rhynia and some minor genera. the essential and most interesting morphological feature is that the simple branching plants bore sporangia at the ends of certain branches without any relation to jeaves or leaf-like organs. sporangites of halle, psilophyton of dawson, and the new genera of kidston and lang represent the earliest known land flora, and though the genera differ in details they all show a remarkable simplicity of structure, with terminal sporangia. their anatomy and morphology are still under discussion, and are of deep phylogenetic and morpho- logical significance. the view put forward by kidston and lang, contrary to that held by most morphologists, is that this ancient family supports the idea that the sporangium of the pterido- phyta is not an organ su? generts. the characeae, an old family still persisting, has received careful handling by j. groves, with the discovery of many beautiful new fossil forms. the bryophytes are still almost unknown as fossils, but two papers on some fossil mosses have recently been published, one palaeontology by walton and another by weyland (1925). certain bryophytic features in the genus hornea from the devonian have led to discussion of the morphology and phylogeny of the groups, but the gaps in the fossil records of mosses are so all embracing that one can only await the discovery of material. algae and fungi —algae and fungi are special palacobotani- cal problems, and the chief recent worker in this field is j. pia who has published a number of smaller and one very large memoir on the siphoneae (1920) but apparently in complete ignorance of the volume on the same subject published by the british museum. incidental to other genera, microscopic fungi are now frequently described, particularly in petrified woods. memoirs on the stratigraphic aspects of fossil plants, describing fossil floras from various localities and horizons, have been numerous, notable cases being the last paper published by the great nathorst, on the culm flora of spitsbergen (1920), a con- tinuation of his famous studies of the fossil floras of the arctic, and the magnificent memoirs by r. kidston, on which he was engaged at the time of his death, of which four parts had been published by the geol. survey, with numerous plates. kidston’s unrivalled work on the british coal measure plants reveals the richness of our native fossil flora, and links up all branches of palaeobotanical work in complete surveys of carboniferous genera. some small memoirs on the german culm come from the pen of robert potonie junior, the son of the famous berlin professor. from the antipodes dr. walkom’s series of memoirs on the fossil impressions and petrified plant remains of quecns- land throw welcome light on an area of which far too little is known. the historically interesting indian gondwana flora is revised in a handsome memoir by seward and sahni (1920) and yabe added to our very scanty knowledge of oriental fossil plants in the memoirs published by the imperial university (1921-2). as general resumes of what has been accomplished, a. carpentier’s revie of palaeobotanical works is invaluable, and we must regret that the two most recent volumes (1923) carry the subject no further than r1g1o. coal—among the most comprehensive works of the old school is the exhaustive memoir, juterrelations of the fossil fuels, by stevenson (1916). an immense amount of more de- tailed work has been accomplished. many of the earlier workers (dawson, williamson, huxley and others) had been interested in the spores and small debris of plants to be seen in sections of some coals, and in recent years lomax had done much to popu- larise in botanical and geological circles, transparent thin sec- tions of coal showing preserved plant remains. stimulated by the importance fuels assumed in the war, more exact correla- tions and investigations into coal structure were attempted. stopes and wheeler’s afemoir on the constitution of coal (1918) was shortly followed by stopes’s paper on the “ four visible constituents in banded bituminous coal ” (1919) in which the four ingredients fusain, durain, clarain and vitrain were detected and diagnosed. these terms have passed into the universal nomenclature (see coat). the chemical, coking and other properties of the constituents have been studied tn further detail by whecler, lessing, sinnott, tideswell and others. somewhat similar work is also being carried on in japan by iwasaki (see a fundamental study of japanese coal, 1920-2) and in the united states by jeffrey, white and thiessen. the latter’s work introduces the name “ anthraxylon ” to represent “woody tissue’ and applies it at times where woody tissue is not proved to have existed, and treats it as though it were the equivalent of “ vitrain ”’ which itis not. in spite of this, however, rapid advance in our knowledge of the marvellous masses of mummified plants is being made. the mass of coal is no longer looked on as a unit, but the attempt is being made to separate out its component parts and to arrive at the chemical and palaeontological structure of minute zones of coal, which contain portions differing both in their anatomical, physical and chemical natures, the ash con- tent, coking qualities and other correlated features. bibliography.—the bibliographies in the following books will give most of the references, except monographs published recently :— 13 e. w. berry, lower cretaceous deposits of maryland (1913), and upper cretaceous and eocene floras of south carolina and geargia (washington, i914), and many other quarto memoirs published by u.s. geol. surv.; j. m. coulter and c. j. chamberlain, morphology of gymnosperms (chicago, 1910); e. c. jeffrey, the slnatomy of woody plants (chicago, 1917); d. h. scott, studies in fossil botany, ed. 3 (london, 1920-3); a. c. seward, fossil plants, vol. 1 to 4 (cambridge, 1917); m.c. stopes, catalogue of cretaceous plants in the british museum, vol. 2 (london, 1915); m. c. stopes and r. v. wheeler, the constitution of coal (london, 1918); r. e. torrey, the comparative anatomy and phylogeny of the contferales, pt. 3 (boston, 1923); g. r. wieland, american fossil cycads, vol. 2 (washington, 1916), {(m. c. s.)",
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