298 PEACTICAL BOTANY 



Pteridophytes once were much more abundant than they 

 now are, and were prominent in the earth's flora during the 

 chief coal-forming ages. Some classes have ceased to exist 

 and others are now represented by relatively few species. 



Once the horsetails, or scouring rushes, and the club mosses, 

 or ground pines, contained many tree-like forms. Now the 

 first class contains but one genus and a score or more of 

 species, and the second contains two genera and several 

 hundreds of species. The water ferns consist of four highly 

 specialized genera. In the Equisetinese and the Lycopodineae 

 sporophylls are arranged in a spike or cone (strobilus). In 

 one genus (^Selaginella) of the class Lyeopodineee two kinds 

 of asexual spores are borne, — one which, upon germination, 

 produces the male gametophyte, and one which produces the 

 female gametophyte. Within this female gametophyte the 

 embryo sporophyte is produced. 



275. Classification : 



Pteridophytes 



Class I. Filieinese (the true ferns). Leading genera used as illustra- 

 tions, — Pteris (the bracken fern), Alsophila (a tree fern), Adianlum 

 (maidenhair fern), Camplosorus (the walking fern), Osmunda 

 (royal fern and Clayton's fern), BolrycMum (the grape fern), 

 Onoclea (sensitive fern and ostrich fern), Satvinia and Marsilia 

 (water ferns) 



Class II. Equisetinese (scouring rushes, or horsetails). Genus used 

 as illustration, — Equisetum (the only living genus of the class) 



Class HI. Lycopodineae (club mosses, or ground pines). Leading 

 genera used as illustrations, — Lycopodium and Selaginella (the 

 living genera of the class) 



