NA TURE 



53 



THURSDAY, NOVEMBER 15, 1900. 



FOSSIL PLANTS AND EVOLUTION. 

 Studies in Fossil Botany. By D. H. Scott, F.R.S. Pp. 

 xiii + 533. (London : Adam and Charles Black, 1900.) 



THE present work owes its origin to a course of lec- 

 tures delivered at University College in 1896. In 

 appealing to a wider audience, Dr. Scott has rendered 

 an important service to biological science, and has placed 

 before the botanical student some of the most striking 

 results of palaeobotanical investigation, which cannot fail 

 to demonstrate, even to the most sceptical, the supreme 

 value of fossil records from the evolutionary standpoint. 

 The author expressly states in the preface that his object 

 has by no means been to write a manual of fossil botany, 



" but to present to the botanical reader those results of 

 palaeontological inquiry which appear to be of fundamental 

 importance from the botanist's point of view." 



The study of petrified fragments of Palaeozoic plants 

 has of late years contributed more trustworthy and im- 

 portant data towards the solution of phylogenetic problems 

 than any other department of paheobotany. It is, how- 

 ever, most desirable that the student should recognise 

 that the range of fossil botany is wide, and that results 

 of primary importance may be reasonably expected also 

 from investigations along other lines than those which 

 are followed in the present work. 



A word of praise is due to Mr. Gwilliam, who has 

 drawn the majority of the admirable illustrations. After 

 a brief introduction, the author proceeds to deal with 

 the most important Palaeozoic representatives of the 

 Equisetales, Sphenophyllales, Lycopodiales, Ferns, Cy- 

 cadofilices and Cordaiteas ; a short account is given also 

 of Mesozoic Gymnosperms. The concluding lecture, in 

 which the general results are summarised in a clear and 

 convincing style, is of special interest as one of the most 

 striking contributions towards the scientific construction 

 of botanical genealogies that we have ever read. In the 

 lectures on the Equisetales we have a concise account of 

 the extinct ancestors of the modern Horsetails, more par- 

 ticularly of the somewhat comprehensive genus Catamites 

 and of the various types of fructification included in the 

 Calamarieae. Lecture iv. treats of the extinct group 

 Sphenophyllales, including Sphenophyllum and Cheir- 

 ostrobus ; the latter genus, originally described by its 

 author — Dr. Scott — in 1897, is of primary importance as 

 enabling us to connect together such apparently distinct 

 phyla as the Equisetales, Lycopodiales and Spheno- 

 phyllales. Three lectures are devoted to the Lycopo- 

 diales. Satisfactory restorations of extinct plants are 

 always a difficulty ; that of Lepidodendron elegans hardly 

 does justice to what must have been one of the most 

 striking and beautiful trees in the forests of the Palaeozoic 

 era. Although our knowledge of the anatomy of 

 Lepidodendron is in several respects fairly complete, 

 there are still a i^^^ points on which further information 

 is much to be desired. 



Dr. Scott suggests "a certain similarity" to Isoetes as 



regards the manner of secondary growth in a Lepido- 



dendroid stem, and refers to " considerable difficulties " 



presented by the phloem of the Lepidodendreae, without 



NO. 1620. VOL. 63] 



dealing with these questions at length. We are, I believe, 

 still in want of satisfactory evidence of the existence of 

 typical phloem, which was added to by cambial activity, 

 at least in the case of the vegetative shoots of the Lepi- 

 dodendreae. The account of the leaves oi Lepidodendron 

 is particularly interesting ; the stomatal grooves on the 

 lower surface of the leaf suggest a xerophytic adaptation^ 

 Indications of xerophytism are afforded by other ana- 

 tomical characters in certain Palaeozoic types, and we are 

 tempted to express the wish that a lecture had been de- 

 voted to the consideration of such evidence as is avail- 

 able bearing on the physiology and biology of Palaeozoic 

 plants. The nature of the large scars on the well-known 

 Ulodendroid branches is admittedly still unaccounted 

 for ; it would have been a satisfaction to have a new and 

 carefully made drawing of the often quoted specimen,, 

 described by Mr. D'Arcy Thompson in 1880, which is 

 considered by many to prove that the scars are the result 

 of the mutual pressure between the bases of cones and 

 the stems which bore them. 



One of the most striking cones included in the account 

 of various Lepidostrobi is an excellent heterosporous 

 type, which was in all probability borne on the well- 

 known stems known as Lepidodendron Veltheimianum. 



In referring to the enormous output of spores neces- 

 sitated by the arboreal habit of the Lepidodendreae, an 

 allusion is made to an exceedingly important discovery, 

 which has not yet been published in full, of a Lepido- 

 dendroid strobilus possessing seeds. This new Cardio- 

 carpon-heanng cone, which Dr. Scott has recently inves- 

 tigated, is of great interest, as showing that " some of 

 the Palaeozoic Lycopodiales actually crossed the frontier 

 line which separates Sporophyta from Sperm aphyta." 

 This discovery naturally suggests an additional argument 

 in favour of a possible connection between the Lyco- 

 podiales and Coniferae ; but, on the other hand, as we are 

 reminded in the concluding lectu re, there are difficulties 

 in the way of connecting the Coniferae with the Lycopods, 

 and arguments are not wanting in favour of the view 

 that the Gymnosperms as a whole may have had a 

 common origin from the Filicales. 



The differences between Sigillaria and Lepidodendron 

 and the exact morphological nature of Stigmaria are, as 

 the author notices, points on which further light is needed. 

 Recent research has added enormously to our exact 

 knowledge of numerous extinct types which were until 

 lately unknown ; it has also taught us that we have still 

 much to learn with regard to some of the commonest 

 fossils from the Coal-measures. 



A photograph is given (p. 207) of a transverse section 

 of a Sigillarian stem, which was briefly described some 

 years ago by Mr. Carruthers, but it is to be regretted 

 that no account of the anatomy of this stem has ever 

 been published. It is unfortunately very rare to find an 

 undoubted Sigillaria in which the tissues are preserved^ 

 and we would express the hope that the example referred 

 to in Lecture vii. may not remain much longer undescribed. 



In the lectures on ferns, the most important new facts 

 are those relating to the Botryopterideae, which are now 

 shown to afford among the Filices a striking instance of 

 the combination of affinities in one extinct family. The 

 account of this family is particularly interesting. 



Dr. Scott's critical and thorough investigations have 



D 



