494 



A TEXTBOOK OF BOTANY 



[Ch. XII 



bution of Pteridophytes, because it prevents their extensive 

 occurrence in very dry places. 



The living Pteridophytes number some 4500 species, and 

 many more are known in the fossil state. Few have any 

 economic importance. They fall into three classes. 



Class 1. Filicineje: the Ferns. 



Class 2. Equisetine^e : the Horsetails. 



Class 3. Lycopodine.e : the Club Mosses. 



Class 1. Filicine.^e: the Ferns 



These include the Ferns par excellence of our own woods, 

 with the more abundant and larger kinds, which are even 

 true trees, in the tropics, where also 

 occur some very delicate and filmy forms. 

 Here belong also some small " Water 

 Ferns," very different in aspect. The 

 class contains three principal orders. 



Order 1 . Ophioglossales : the Adders 



Tongue Ferns. 

 Order 2. Filicales: the Ferns proper 

 OrderS. Hydropteridales: the Water 



Ferns. 



Order 1. Ophioglossales : the Adder's 

 Tongue Ferns. This small order is chiefly 

 important because of the primitive char- 

 acter of its members. It includes the 

 Adder's Tongue (not to be confounded 

 with the liliaceous plant of that name) 

 and the Moonwort of our own flora (Fig. 

 349). Upon the stalks of single leaves 

 rising from underground root-stocks are 

 developed close spikes of thick-walled 

 (etjsporangiate) sporangia, which con- 

 trast markedly with the thin-walled type 

 (leptosporangiate) of the true Ferns. 



Fig. 349. — The 

 Adder's Tongue 

 Fern, Ophioglossum 

 vulgatum ; X f. 

 (From Bennett and 

 Murray.) 



