2 2 HEREDITY AND EVOLUTION IN PLANTS 



arid is usually slightly curved, while the remainder, the 

 venter, is imbedded in the tissue of the cushion. As the 

 archegonium approaches maturity it is seen to contain 

 three cells; a long neck-canal cell, nearly fiUing the neck, 

 an egg-cell or ovum, filling the venter, and between these 

 two a ventral-canal cell. The egg is the female reproduc- 

 tive cell. As it matures, the other two cells become disin- 

 tegrated into a mucilaginous mass that fills the neck-canal. 

 Since the archegonia contain the eggs they are the female 

 reproductive organs. 



Fig. 22. — Portion of a clross-section of a prothallus of a fern [Adian- 

 tum), showing an antfieridium (an), and sporogenous cells within. 

 (Drawn from preparation of E. W. Olive.) 



15. Reproductive Organs : Antheridia.^Search among 

 the rhizoids will reveal another class of organs, the an- 

 theridia, globular and also having walls only one cell 

 thick. These are the male reproductive organs. At 

 maturity they contain a large number of tiny motile cells, 

 composed chiefly of a coiled nucleus, and able to swim 

 about in water by the vigorous lashing of numerous little 

 thread-Hke cilia attached to one end. These are the 

 sperms, or male reproductive cells (Figs. 22 and 23.) 



