October 13, 1910] 



XATURE 



473 



SOME RECENT STUDIES OF l-OSSIL I'LAXTS. 

 WJHES, many years hence, a history of the study of 

 ' ^ fossil plants during the first decade of the twentieth 

 century is being elaborated, it will be found that two 

 discoveries, announced in 1903 and 1906 respectively, will 

 stand out as particularly far-reaching in their " after 

 elTects. " These contributions will be found to rank in 

 importance with any that may be cited in the whole range 

 of the previous history of the study of pala;obotany. 



in 1903, Oliver and Scott showed that Lyginodendron, a 

 well-known fern-like plant of the Carboniferous period, was 

 in reality a seed plant. Within the next two years :i 

 number of similar discoveries were made in the case of 

 several other genera, though since 1905 no further contri- 

 butions of a like nature have been published. The identifi- 

 cation, however, in that year of the male organs of l.ygino- 

 dendron, which we owe to Dr. Kidston, completed our 

 knowledge of that genus. 



In 1906, Dr. Wieland, in his handsome volume on the 

 ■■ American Fossil Cycads," brought home to us, with a 

 vividness which left little to be desired, the amphisporangiate 

 nature of the cone of the Mesozoic genus Bennettites, or 

 Cvcadeoidea, as the Americans prefer to call it. 



As Wieland himself foresaw, this discovery has thrown 

 light on the phylogeny of the Angiosperms and Gnetales,' 

 two groups hitherto of obscure affinities. These contribu- 

 tions have been already reviewed in Nature' at some 

 length, and it is therefore not proposed to discuss them 

 further here. 



.\ very e.>ctensive series, amounting to several hundreds, 

 of memoirs, both large and small, have also been published 

 on various palaeobotanical subjects within the last ten 

 vears. The results there contained all contribute to our 

 knowledge in one direction or another, but these directions 

 are so varied, and often so disconnected, that it will only 

 be possible to notice a few af them very briefly in a 

 concise review such as the present. Further, the selection 

 here made will be chiefly confined to those which have 

 appeared during the last four years, and especially to those 

 dealing with petrified material. 



The true Ferns of the past have recently received con- 

 siderable attention. It is now recognised that the ancient 

 Ferns of the Palaeozoic period, for which the name Primo- 

 filices has been suggested, differed in certain important 

 respects from the Mesozoic, Tertiary, and recent Lepto- 

 sporangiats. The latter appear to have sprung from the 

 Primofilices, during the latter portion of the Permian 

 period, and it would seem that, very soon after the initia- 

 tion of the group, it differentiated in a fan-like manner 

 into a number of families, many of ^hich are still repre- 

 sented to-day. The Osmundacea?, for instance, which of 

 all the Leptosporangiate ferns stand nearest to the archaic 

 stock, the Primofilices, were in existence in Upper Permian 

 times. 



This fact is emphasised by the recent studies of Kidston 

 and Gwynne-Vaughan,^ on the anatomy of a number of 

 Osmundaceous stems from the Permian, Mesozoic, and 

 Tertiary rocks. Three of these memoirs have appeared, 

 and a fourth has been added since this review was written. 

 This work is especially interesting, for not only is our 

 knowledge of petrified plant remains from the rocks of 

 these periods extremely scanty, but the study of the 

 structure of these ancient representatives of the family 

 has thrown light on the ancestral history of certain 

 structural peculiarities met with in living ferns, especi- 

 ally the origin of the adaxially curved leaf trace.* The 

 primitively solid, protostelic nature of the stem cylinder 

 of the ancient Osmundaceie is emphasised, and the evolu- 

 tion of the stele in this group is no longer a matter of 

 theory, but of fact. 



Our knowledg.; of the Primofilices has also recently 

 advanced rapidly. A full account of this group will be 

 found in the new edition of Scott's " Studies in Fossil 



1 See Arber and Parkin, Proc. I.inn. Soc. Bot., vol. xxxviii., p. 29, T907, 

 and Annalsof Bot., vol. xxii., p. 4S9. igo8. 



2 See Nature, vol. Ixxi., p. 68, 1904 ; and p. 426, 1905 ; vol. Ixxv., 

 p. 529, 1907; vol Ixxvi., p. 113. 1907. 



■^ Kidston and Gwynne-Vauehan, Tran5. Roy. Soc, Edinburgh, vol. xlv., 

 p. 7'^9, 1907; vol. xlvi., pp. 21-5. 6gi, 1908-9. 

 < Gwynne-Vaushan and Kidston, Proc. Roy. Soc. Edinburgh, vol. 

 433. 1908 



Botany " (chapter ix.). Dr. I'aul Bertrand, in his " Etudes 

 sur la Fronde des Zygoptt'rid^es," a handsomely illustrated 

 volume published last year, has traced the course of evolu- 

 tion of the petiolar stele of members of this group. In this 

 connection JNIr. Gordon's paper on the structure of the stem 

 and petiole of Diplolabis roemeri (Solms) from the Calci- 

 feious Sandstone of Scotland, which is shortly to appear 

 in the Transactions of the Royal Society of Edinburgh, will 

 be found of interest as carrying further broad conclusions 

 of a similar, if not identical, character. 



So far as the other Palaeozoic groups are concerned, 

 attention has recently been devoted almost entirely to the 

 Lycopods. The Sigillarias, which until a short time ago 

 remained the one important genus of the anatomy of which 

 we knew very little, especially as regards the numerous 

 species which possessed ribbed stems (Eu-Sigillarise), have 

 now been studied in detail. The structure of the stele 

 closely resembles that of other Pal.Teozoic I-ycopods, especi- 



FlG. I. — Tltamtwpteris Schlccktcndallii, a 



Upper Permian ot Russia. A transverse section >howini: 

 xylem ling; c.xy, central .\ylem ; /.C, inner cortex; sc 

 outer cortex ; i-par, inner parenchyma c' petiole; o.par, 

 chyma of petiole; scl. sclerotic ring of petiole; ?■. , root 

 alter Kidston and Gwynne-Vaughan. 



clerotic 



NO. 2137, VOL. 84] 



ally Lepidophloios, the chief distinguishing features being 

 found in the cortical I issues and leaf-bases. The anatomy 

 of the cone scars is now known.' It has been found that, 

 in certain species of ribbed Sigillarioe, the leaf-trace, when 

 traversing the leaf-base and the lower part of the. leaf, 

 possesses a double xylem strand" (Fig. 2). The ribbing of 

 the stem appears to be quite independent of the leaf-bases. 

 The external features of three species of ribbed Sigillarias 

 have now been correlated with their internal structure. 



The Sigillarias, like the Lepidodendrons, were large 

 forest trees, often 100 feet or more in height. Herbaceous 

 members of the group appear to have been comparatively 

 rare, and until recently have been little known. Halle ^ 



1 Kidston. Trans. Roy. Soc. Edinburgh, vol. xli., p. 533, tgos ; Proc. 

 Roy. Soc. Edinburgh, vol. xxvii., p. 207, 1907. 



- Arber and Thomas, Phil. Trans. Royal Soc. B, vol. cc, p. 133, 1908 ; 

 Ann. of Rot., vol. xxiii.. p. 5ri;, 1Q03. 



•I Halle, Arkiv. (or Botanilt (Stockholm), vol. vii., No. 5, 1907 ; and 

 ibid.y vol. vii., No. 7, igoS. 



