60 TiiK .rouRXAr. of uolaxy 



necessarily conservative. As regards the root, the primary structure 

 is no doubt highly conservative, but it does not follow that the same 

 is true of its secondary tissues. 



The word "reversion " is used in a peculiar sense, for certain effects 

 of wounding, believed by the author and some others to be reminiscent 

 of ancestral characters. This doctrine has hitlierto been employed 

 only in support of certain controversial opinions, and has not yet been 

 adequately subjectejl to impartial criticism. 



The worst of all such " canons " is that every writer 'ajjjilies them 

 as suits his individual views, and treats inconvenient cases as excep- 

 tions. 



In the systematic part of the book we first come to the author's 

 well-known division of the higher plants into Lycopsida, without, and 

 Pteropsida, with, leaf -gaps in the vascular ring, a classification widely 

 accepted, though it is now realized by many botanists that Spheno- 

 phylls and Eepiisetales have little in common with tbe Lj^copod 

 group. 



The author's doctrine of the cortical origin (.f the pitli is applied 

 even to the Lycopods, where the evidence seems peculiarly unfavoiu-- 

 able to this interpretation. It is a pity that the exact developmental 

 processes involved are not more clearly explained. His views on the 

 evolution of the Osmundaceae are well expounded ; the strong case 

 made out would have been more convincing if the facts on the other 

 side, brought forward by Kidston and Gwynne-Vaughan, had been 

 dealt with. 



The lower seed-plants are divided into Archigymnospernne, 

 including Cycadofilicales, Cycadales, C(n'daitales and Ginkgoales, and 

 Metagymnospcrmie consisting of the Conifers and Gnetales. It is 

 well pointed out that GinJcgo forms a link between the two main 

 divisions. The long chapter on Coniferales is chiefly devoted to an 

 exposition of the author's well-known view of the primitive position of 

 the Abietinea;, and especially of Finns, and the derivation of the 

 ancient Araucarinese from that group. This hypothesis is maintained 

 with great ingenuity, in the face of much inherent improbability. 

 The opposite theory of the direct derivation of the Araucarinese from 

 their immediate Palajozoic predecessors the Cordaitese has been con- 

 siderably strengthened by the work of Boyd Thomson and Burlingame. 

 The view, maintained by Wieland and his followers, of an athnity 

 between the Bennettitales and the Angiospei'ms, is rejected. In 

 this connection it may be pointed out that we have no actual proof 

 that fertilization in Beiinettites was by spermatozoids, as the author 

 assumes. 



The chapter on Herbaceous Dicotyledons is imjjortant, for it sets 

 forth in detail the author's theory of their derivation from arboreal 

 ancestors, a view which is well worthy of consideration. The author 

 believes that the fresh and vigorous herbaceous vegetation will tend 

 in future to supplant the forest trees ; he has no such hopes, however, 

 for the Monocotyledons, which he acutely remarks (p. 198), may be 

 said to represent the second childhood of the vascular plants. " This 

 group seems to have reached such a high degree of specialization that 

 it will probably in the long run entirely disappear and be replaced by 



