52 ON GENERA AND SPECIES. 



ing sixty-four plates, the drawings of the latter as well as 

 part of the preceding being derived from living plants of 

 the Kew collection. The practical use of these works is 

 in assisting to determine species, and which, either under 

 the same name or as synonyms, will be found in his last and 

 great work the " Species Filicum," the most important 

 systematic work on Ferns yet published, being a description 

 of all known Ferns, particularly of such as exist in the 

 author's herbarium (previously noticed), and such as are 

 with sufficient accuracy described and figured in the works 

 of other authors. It consists of five volumes, the first of 

 which appeared in 1846, and the fifth in 1864, its prepara- 

 tion having occupied his leisure time for a period of not 

 less than twenty years. It treats of the orders Gleicheni- 

 acece and Polypodiacece only, of which 2,401 species are 

 described, with their synonyms, which amount to about 

 4,300, as also their native countries and names of collectors, 

 illustrated with 300 plates representing 522 species. He 

 arranges the whole under sixty-three genera, fourteen 

 of which contain only one species each, thus present- 

 ing a great contrast to the mass of species which he 

 continues to retain under the characters assigned by Lin- 

 naeus and Swartz, to such genera as Polypodium, Aspidium, 

 Pteris, and Acrostichum, thus avowing his preference for 

 large genera by strictly adopting the characters derived 

 solely from the fructification. With regard to which he 

 says, " Increased study has, he must confess, strengthened 

 his conviction that those botanists who have shown them- 

 selves peculiarly addicted to multiplying genera have not 

 always taken nature as their guide, nor succeeded in 

 eliciting a simple nor tangible arrangement, yet have their 

 close and accurate investigations thrown a new light on the 

 study of Ferns, a light which cannot fail to aid the re- 



