PTERIDOPHYTA 



245 



Gametophytes. The male gametophyte, like that of Selaginella, is 

 developed inside the microspore and similarly consists of a small prothal- 

 lial cell and an antheridium (Fig. 203). The latter has a sterile jacket of 

 four cells investing four spermatogenous cells, each of which gives rise to a 



Fig. 202. Cross section of small portion of a microsporangium of Isoetes nuttaUii, showing 

 the wall, tapetum, a trabecula, and spore mother cells, X400. 



A 



B 



F G H I J 



Fig. 203. Male gametophyte of Isoetes lacustris. A, microspore; B, prothallial cell cut 

 ofT; C to F, formation of four jacket cells and primary spermatogenous cell; G and H, divi- 

 sion of spermatogenous cell; / and J, formation of four sperms. H and / sectioned at right 

 angles to G and I. (After Licbig.) 



single sperm. It is noteworthy that only four sperms are produced, as 

 this is the lowest number in pteridophytes. The sperms are large, coiled, 

 and multicihate, thus differing from those of the other Lycopodiinae 

 (Fig. 2ME). 



