234 



PLANT MORPHOLOGY 



Gametophytes. The male gametophyte of Selaginella is developed 

 entirely within the microspore. It is without chlorophyll and greatly 

 reduced. Its development is initiated before the spore is shed from the 

 sporangium and is completed later. A small prothallial or vegetative cell is 



Fig. 190. Development of the microsporangium of .SeZagweZZa (7oZeo«M, X320. yi, median 

 longitudinal section of portion of apex of strobilus, showing early stages; B, slightly later 

 stage with ligule to the left; C, young sporangium with sporogenous tissue surrounded by 

 tapetum and two wall layers; D, older sporangium, the sporogenous cells beginning to 

 round up. 



cut off, the large remaining cell forming a single antheridium (Fig. 193). 

 At first this consists of four primary spermatogenous cells surrounded by a 

 sterile jacket of eight cells, and usually the male gametophyte is shed from 

 the microsporangium in this condition. Later the spermatogenous cells 

 increase in number to 128 or 256, each finally giving rise to a sperm. 

 Meanwhile the jacket cells disintegrate, leaving the mass of sperms free 

 within the microspore wall. The sperms are small, curved, and biciliate. 



