244 PTERIDOPHYTA. [CH. 



able to contribute facts of the greatest interest and importance 

 towards the advancement of botanical science. 



The botanist's chief aim in the anatomical investigation of 

 Palaeozoic genera is to discover data which point the way to a 

 solution of the problems of plant-evolution. In the abundant 

 material afforded by the petrified remnants of ancient floras we 

 have the means of tracing the past history of existing groups or 

 individual forms, and it is from the Palaeozoic Pteridophytes 

 that our most valuable results have been so far obtained. 



In this 'and the following chapters of Volume I. two 

 divisions of the Pteridophyta are dealt with in such detail as 

 the nature of the book allows. In the earlier chapters of 

 Volume II. the remaining representatives of this class will be 

 described. As in the preceding chapters such recent plants 

 will be described as are most essential for the correct interpre- 

 tation of the fossil forms. 



It is impossible to do more than confine our attention to 

 a few only of the genera of living plants which directly concern 

 us ; some acquaintance with the general facts of plant morpho- 

 logy must be assumed. Among the most useful text-books or 

 books of reference on the Pteridophyta the student may consult 

 those mentioned in the footnote'. 



I. EQUISETALES. 



Leaves usually small in proportion to the size of the whole 

 plant, arranged in whorls at the nodes. Sporangia borne on 

 specially modified sporophylls or sporangiophores, which are 

 aggregated to form a definite strobilus or spore-bearing cone. 



Equisetaceae. (Recent Species.) 



The leaves are in whorls, coherent in the form of a sheath, 

 and traversed by longitudinal veins which do not fork or anasto- 



' Scott (96) a text-book for elementary students ; a full account is given of 

 Equisetum and other genera of primary importance. Vines (95) Part iii. 

 Campbell (95), Luersseu (89) in Eabenhorst's Kryptogavieii-Flora, vol. in., Van 

 Tieghem (91), de Bary (84), Baker (87). 



