REVIEWS 519 



features of the Equisetales with those of the Lycopodiales and obviously closely 

 related to Sphenophyllum, is critically examined and placed in a suborder of Cheiro- 

 strobas, which with the Sphenophylle^e are placed into the group Sphenophyllales. 

 These on careful consideration of all the available evidence Prof. Seward 

 does not unite with the Psilotacece, as has been done recently by Thomas and 

 Bower, though undoubtedly there are some curious resemblances between 

 Psilotum, and still more between Tmesipteris, and the Sphenophyllales. On the 

 other hand the differences between Psilotaceae and the bulk of the Lycopodiales 

 warrant in the author's mind their separation from the Lycopodiales. 



The account of the Psilotales and of the recent Lycopodiales is altogether 

 excellent, and the full discussion of morphological and anatomical features of 

 the recent members of each group is of the utmost value, particularly to students 

 of geology desiring to take up seriously the study of fossil plants. But 

 botanical students could not desire a more concise and at the same time critical 

 description of the leading members of these groups. 



The Lepidodendraceae are dealt with in the masterly manner natural to one 

 who has contributed so largely to our knowledge of this group of plants. 



We note that Prof. Seward retains Binney's designation of Lepidodendron 

 vasculare for the more usual Lepidodendron selaginoides of Sternberg. While 

 accepting his arguments in favour of the adoption of this specific name as valid, 

 one cannot help expressing a hope that after the decisions arrived at by 

 the recent International Congress at Brussels, some uniformity of practice in 

 PaUeobotanical nomenclature will be established. The difiiculties with which 

 Palaeobotanists are faced in deciding which name to adopt in the case of plants 

 of which the various organs are discovered separately and only subsequently 

 correlated are often very trying. 



In dealing with the histological features of the Lepidodendracere we note with 

 interest the suggestion that the fine bars which connect the horizontal bands of 

 the scalariform thickening in the tracheae are suggested as possibly representing 

 a partial absorption of the pit-closing membrane which in many recent and fossil 

 forms has entirely disappeared according to Gwynne Vaughan. 



The very vexed question as to the nature of the Ulodendroid scars is fully 

 discussed, and the author inclines to the adoption of the branch-scar hypo- 

 thesis and makes the useful comparison with the phenomenon of cladoptosis as 

 observed in certain Conifers and even Dicotyledonous trees. 



It will be noticed that the genus Bothrodendron, our knowledge of which 

 is now more complete than of any of the fossil Lycopodiales, is placed by Prof. 

 Seward in a special subdivision of Bothrodendreje ; for though both in its external 

 appearance and internal structure it bears considerable resemblance to the genus 

 Lepidodendron and was often included in that genus, yet certain substantial 

 differences of structure, and more particularly the knowledge we have now gained 

 of its strobilus, warrant the separation of this genus from the Lepidodendreas. 

 The ultimate position of Lepidocarpon and Miadesmia in the group of Lycopodiales 

 is cautiously left for the moment in suspense. 



In the group of Filicales our knowledge of recent as well as of fossil forms has 

 been considerably advanced of late years, and Prof. Seward gives us a clear 

 and concise account particularly of those features which are of importance in 

 interpreting the structure and relationship of fossil forms. A much-needed word 

 of caution is given in describing the variation in the leaf forms of recent ferns 

 many of which, if met with in isolated specimens as fossils, would undoubtedly 

 have given rise to a multiplication of species. The evolution of the more 



