17 



Plant ' which is the result of the union of the 

 sperm and egg-cell, and which, when it is adult, 

 produces the asexual spores. The former is 

 known as the sexual generation, the latter as 



FIG. 5. Young fern plant attached to Prothallus. 

 F/. = First frond ; FR. = First root ; /?/.=- Rhizoids of Prothallus. 



the asexual. Neither of these generations can 

 be produced independently of the other ; there 

 must be an interposition of the one generation 

 between two of the other. The life-cycle of 

 the fern thus shows what is known as the 

 2 



