The Gtossopteris Ftora. 33

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1 The Gtossopteris Ftora. 33 exaniple of the filling-tissue described by Count Solms. A comparison of the figures given by Schuster with those in Solms' paper leaves no doubt as to the correctness of this conclusion. A.C.S. THE GLOSSOPTERIS FLORA. " On the Geological Structure and History ot the Falkland Islands." By T. G. Halle. (Reprinted from the Bull. Geol. Iiistit. Univ. Upsala, Vol. XL, p. 115, 1911). "Les phenomfenes glaciaires de Tepoque Permo-Carbonif^re : indications climateriques fournies par le flore." By P. Bertrand. (Ann. soc. geol. du Nord, Vol. XXXVIII., p. 92, Lille, 1909). ALTHOUGH the title of Dr. Halle's memoir does not afford any indication of the fact, some of his results are of considerable botanical interest. He describes certain fossil plants wbich demonstrate the existence of the Glossopteris flora in the Falkland Islands, and in association with the plant-beds he discovered rocks of undoubted glacial origin. The term Glossopteris flora, first used by Neumayr in 1887, is applied to an assemblage of Paljeozoic plants from India and the southern hemisphere characterised by a comparatively small number of species, by a wide geographical distribution, and by a general uniformity of facies. Our knowledge of the nature of the individual members of the flora is very meagre as it is based almost entirely on casts and impressions of leaves and stems, but from the point of view of distribution and climatic conditions the flora presents many features of interest. During the Permo-Carboniferous era the vegetation in Europe, parts of Asia, and the southern hemisphere was of a uniform type and included such genera as are familiar to students of the Coal-Measures flora of Britain. The comparatively small number of species obtained from the Permo-Carboniferous rocks in India, South Africa, South America, and Australia point to the existence of a flora characterised by the predominance of Glossopteris and Ganganiopteris (usually spoken of as Ferns but probably Pteridosperms) with some other genera unrepresented in the northern flora and differing in the absence or rarity of many plants which form a characteristic feature in the Coal Measures of Europe and North America. The Glossopteris beds in India are spoken of by Geologists as Lower Gondwana, and Professor Suess instituted the name " Gondwana Land " for a former Southern Continent, now represented by S. Africa, S. America, Australia, and India, in which the Glossopteris flora flourished. The occurrence of ice-formed rocks in close association with the Glossopteris beds is frequently brought forward as evidence of different climatic conditions in the two Permo-Carboniferous botanical provinces and it is generally believed that the contrast between the floras is in large measure the expression of different climates. It is with questions relating to climate that M. Bertrand's paper is chiefly concerned.' In his introduction to the account of the Falkland islands. Dr. ' The distribution and the composition of the Glossopteris flora are fully dealt with by Mr. Arber in his valuable Monograph issued by the Trustees of the British Museum [Catalogue of the Fossil Plants of the Glossopteris Flora in the Department Xslociation Meeting at Stockport in See also E. Koken, lndisches Perm und die permische E.szeit. Neues Jahrb. fiir Mineralogie, Festband, 1906, p. 446.

2 34 Notes on Recent Literature. Halle remarks that since Darwin's time, with the exception of some investigations made by members of the Challenger expedition in 1876, until the Swedish expedition visited the islands in , the geology of the islands has been almost entirely neglected. It was as a member of a smaller expedition undertaken by a few Swedish naturalists in 1907 that Dr. Halle made the discoveries with which this note is primarily concerned. Professor Andersson, the leader of the Swedish Polar Expedition ( ), collected a few imperfectly preserved fossil plants, one of which is described by Professor Nathorst' as a species of Phyllotheca, an Equisetaceous genus characteristic of the Glossopteris flora of India and the Southern Hemisphere and recorded also from a few Palseozoic and Mesozoic strata in Europe. The occurrence of this genus suggested the forecast, justified by Halle's investigations, that other and more convincing evidence of the existence of the Glassopteris flora would probably be discovered in the Falkland islands. A considerable portion of the islands is occupied by Devonian rocks fiom which a few fragmentary plants have been obtained. Some small pieces figured by Halle bear a fairly close resemblance to Lepidodendron nothuin Ung. and L. australe McCoy, Lower Carboniferous and Devonian species. A point of general interest in regard to the occurrence of a marine Devonian fauna in the Falkland islands is that a similar fauna has been recorded from South Africa, Australia, and the Argentine Republic. It would appear, however, that the Falkland fauna is distinctly more closely allied to that of South Africa than to the fauna of the far nearer Devonian areas in South America. Dr. Halle discovered Glossopteris leaves and other genera characteristic of the Glossopteris flora at several localities in east Falkland and at the south point of Speedwell island. The presence of these plants points to correlation of the Falkland strata with the Lower Gondwana beds of India and other countries in which the Glossopteris flora existed. Dr. Halle adopts the term Lafonian for the Falkland Gondwana series and from these beds he describes the following species : Phyllotheca atistralis Brongn., represented by several imperfect pieces of stems and leaf-sheaths, in themselves hardly sufficient to establish the occurrence of the Glossopteris flora ; another species of Phyllotheca, compared by Nathorst with the Siberian P. deliquescens Schmal.; Glossopteris Browniana Brongn. and G. indica Schimp. the commonest plants in the series; Glossopteris aiigustifolia Brongn. and G. damudica Feist.; Gangamopteris cyclopteroides Feist.; Dadoxylon lafoniense and some other less satisfactory forms too imperfect to be determined with certainty. As Halle points out, this flora is undoubtedly to be correlated with the Lower Gondwana flora of India, South Africa, Australia, and South America. It is customary in speaking of these southern plant-beds (in which the Glossopteris flora has been found) in terms of northern hemisphere stratigraphy to employ the comprehensive designation Permo-Carboniferous, as it is as a rule impossible to correlate them precisely with northern equivalents. The important point is that the rich flora from the Coal Measures of Europe and North America, which closely resembles that of the succeeding Permian period, is replaced in India and many regions south of the equator by one in which Glossopteris and Ganagmopteris are the most abundant genera, while most of the characteristic northern ' Nathorst, A. G., Bull. Geol. Instit. Upsala, Vol. VII, 1906.

3 The Glossopteris Flora. 35 types are unrepresented. It is noteworthy that Lepidodendron and Sigillaria occur in association with Glossopteris in South Africa and South America and the long strap-shaped leaves which are not uncommon in the Glossopteris beds and are usually assigned to Neegerathiopsis may be identical witli the northern genus Cordaites. Making due allowance for the fact that authors are not infrequently led to give undue importance to wide geographical separation by the tise of different names for very closely allied plants, and admitting that further research may connect more closely the Permo-Carboniferous floras on the two sides of the equator, the statement holds good that there is evidence of the existence of two more or less well-marked botanical provinces in the latter part of the Palaeozoic era. Dr. Halle gives an interesting account of the Lafonian glacial beds which occur immediately below the plant-bearing strata and shows clearly by his description of the rocks, some of which he speaks of as tillites (a term instituted by Professor Penck), and striated rock-floors that in the Falkland islands, as in other countries, where the Glossopteris flora occurs, sheets of ice were spread over the land surface of which the Falkland islands are a diminutive survival. The question of the widespread ice-action in the southern hemisphere and in India in relation to the Glossopteris flora is dealt with by M. Paul Bertrand who gives a clear summary of the chief geological and botanical facts. After a brief reference to some of the hypotheses advanced by way of explanation of the glaciation during part of the Paleozoic period, he remarks that geologists have appealed for confirmation of their views to palseobotanists and to meterologists. Unfortunately, he adds, the study of Carboniferous and Permian floras instead of facilitating the solution of the problems raised by the association of the Glossopteris flora and iceformed rocks, raises fresh difficulties. The fact that some of the northern genera such as Lepidodendron and Sigillaria, typical European Coal-Measure plants, grew in South Africa and South America in regions recently emerged from glacial conditions suggests the possibility that the vegetation of the Coal period north of the equator may have flourished in a temperate rather than in a tropical climate. He proceeds to quote certain conclusions regarded by some authors as favourable to this view, adding that if the northern flora grew in a temperate climate the lowering of temperature in the south, sufficient to bring about glacial conditions and to effect such a change in the vegetation as is revealed by a comparison of the two floras, need not be very great. There are, however, serious objections to the acceptance of the view that the nature of the Upper Carboniferous and Permian plants of Europe and North America is consistent with a temperate climate. M. Bertrand points out that it has been frequently asserted that Lepidodendron and other Carboniferous plants indicate by their anatomy adaptation to an environment physiologically dry ; but it is significant that the xylem elements in Lepidodendrese are very much larger than those of recent conifers. The diameter of the tracheae in the former varies from 100 to 125/*; in the latter from 20 to 25/x. In spite of the abundance of water which is suggested by the unusual size of the conducting channels, M. Bertrand adds, the Lepidodendrese endeavoured to limit their transpiration. The stems possessed a thick covering of cork ; the leaves were reduced in breadth and

4 36 Notes on Recent Literature. were protected against excessive loss of water by a hypodermal sheath of sclerenchyma and by a thick palisade tissue. The stomata were sunk in grooves. The opinion has been expressed that the xerophilous characters of the Coal-Measure plants may be the result of growth in salt water ; but this would not account for all the facts. The occasional alternation of zones of crowded and more widely separated leaf-scars on Sigillarian stems may be the expression of variation in the rapidity of growth. The absence of reglilar rings of growth in the wood of Lepidodendron and other genera points to a uniformity of climate throughout the year. Dr. Gothan has recently written a short paper on the absence of annual rings in the stems of many Palseozoic plants and the bearing of this fact on questions of climate.' Without discussing his remarks on the main point, reference may be made to a criticism on the generally accepted view, adopted by Bertrand, namely that the occurrence of the Glossopteris flora in rocks closely associated with ice-formed material necessarily implies that the plants grew in a cold climate. He quotes the existence of a Mediterranean flora in the north of Italy on glacial moraines of the great ice age as an illustration of the falsity of the conclusions as to the Glossopteris flora. But it may be asked, is the conformable succession of Permo-Carboniferous glacial beds and the plant-bearing strata strictly comparable with the unconforinable juxtaposition of the Mediterranean flora and the deposits of the ice age? The wide distribution of what has been called the boreal flora indicates an absence of climatic zones, and the temperature could hardly have been lower than that of our summer. The xerophytism of the Carboniferous plants, their rapid growth, and the large diameter of the tracheae are regarded by Bertrand as evidence in favour of a tropical climate. On the other hand, in the southern hemisphere and in India there was extensive glaciation at a time when this presumably tropical flora flourished in the north. The study of the structure of Paleozoic plants has made remarkable strides during the last few decades, but as yet little attention has been paid to anatomical data from a physiological or ecological standpoint. M. Bertrand's summary shows what contradictory results may be obtained from a cursory examination of anatomical evidence; it should also have the effect of stimulating palieobotanists to pursue a line of inquiry likely to yield interesting results and, incidentally, his paper emphasises the need for experimental work on recent plants. A good beginning has been made by Mr. Hamshaw Thomas in his investigation of the leaf-structure of Catamites which lead him to the conclusion that " the structure of the smaller leaves probably indicates that they grew in a moist situation, or where the atmosphere was humid. The larger leaves are more xeromorphic in character." ^ In the concluding portion of his Presidential Address to the Botanical Section of the British Association Meeting at Portsmouth this year (1911) Professor Weiss gave an exceedingly interesting illustration of the application of data furnished by ecological investigations to the biology and ecology of the plants of the Coal period. A.C.S. > Die JahresringlosiUeit der palaozoischen Baume und die Bedeutung dieser Erscheinung fur die Beurteilung des Klimas dieser Perioden, Naturwiss. Wochenschrift, [N.F.] Bd X No. 28, ^ On the leaves of Ca/aOTrtfs (Calatnocladus section), JPhil. Trans fl. Sof,, Vol, 202, p. 51, 1911,

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