CHAPTER XIII. — -THE PTERIDOPHVTA. 



361 



cultiva- 



numerous small spores. Several species are common in 

 tion as green-house plants; 

 Selaginella apus, not an uncom- 

 mon native species, grows in 

 damp places, and might easily 

 be mistaken for a Moss, and 

 Selaginella rupestris, which has 

 the aspect of a small Lycopo- 

 dium, is common on rocks and 

 in dry, sandy soil. Fig. 567 rep- 

 resents a portion of a fructify 

 ing stem of a Selagi- 

 nella with a micro- 

 sporangium and a 

 macrosporangium 

 enlarged. 



Fig. 567. — Fruiting branches of 

 Selaginella, about natural size, a, 

 spore-bearing portion; b, sporangi- 

 um containing microspores, from the 

 inner surface of one of the scales; 

 c, sporangium from the inner surface 

 of another scale, containing macro- 

 spores. 



The Isoetes. In these 

 species the stem is short, 

 and the numerous leaves 

 with which it is clothed 

 are long and grass-like, 

 and on the upper surface 

 of the sheathing bases 

 occurs a depression or 

 pit in which the sporan- 

 gia are borne, and just 

 above this is the ligule. 

 The macrosporangia con- 

 tain numerous macro- 

 spores, and are borne by 

 the outer leaves of the 



B, the base of one of the leaves, show- 



Fig. 568. — Isoetes setacea. A, the entire plant, 

 ing immature sporangium acid, above it, the ligule. 



