PTERIDOPHYTA 



235 



A - y r-< B 



Fig. 191. Longitudinal sections of young megasporangia of Selaginella, X200. A, mega- 

 sporangium of Selaginella emmeliana with spore mother cells, the functional one enlarging; 

 B, megasporangium of Selaginella apoda, showing three of the four megaspores. 



Fig. 192. Longitudinal sections of sporangia of Selaginella emmeliana, X80. A, a micro- 

 sporangium with numerous microspores; B, a megasporangium with three of the four 

 developing megaspores. 



The female gametophyte develops within the megaspore but is not so 

 greatly reduced as the male gametophyte. The megaspore germinates 

 while still within the megasporangium and long before it has reached its 

 full size. The protoplast of the young megaspore is apically situated and 

 consists of a vesicle with a small nucleus. It has a thick membrane that 

 seems to grow more rapidly than itself, leaving a fluid-filled space between 

 the protoplast and the membrane. The membrane soon differentiates 



