HETEROSPORY 



251 



and cell inside (pr.) from whicli the prothallus will be formed. D, 

 microspore germinated to form antheridium which completely 

 fills the spore cavity. E, microspore opened with sperms em- 

 bedded in mucilage formed from breakdown of walls in water. 

 F, two free flagellated sperms. G, megaspore opened and 

 germinated to form prothallus with three archegonia {ay.), the 

 eggs in two of which have developed into embryos at the expense 

 of the prothaUial tissue, while the third (an) is unfertilised 

 and still contains the egg. 



