f 



THE PTERIDOPHYTA : LYCOPSIDA, ETC. 575 



Antheridium — < / ' . ■ "• >' ■ '' '' 





Empty antheridium , 



V 



. , -I' "■ . 



\ 



1 



.' 4 



Fig. 584. — Lycopodium clavatum. Vertical section of 

 prothallus showing young and old antheridia. 



* " » -^ % 



Fig. 585. — Lycopodium clavatum. 

 Antherozoids from Fig. 584. 

 Greatly enlarged. 



Development of the Archegonium 



The archegonia develop on the same prothallus as the antheridia, but 

 towards the margins. Many archegonia are normally formed, but only one 

 develops after fertilization. The archegonium arises from a superficial 

 cell which divides into two. The outer cell forms the neck, which is here 

 long and straight, as in the Bryophyta. The inner cell divides again, into a 

 primary canal cell and a primary ventral cell. The former gives rise to 

 about six neck canal cells, while the latter probably functions directly as 

 an oosphere. The resemblance to the Bryophyta in these homosporous 

 forms is all the more striking because in the heterosporous Selaginella and 

 Isoetes the archegonium has undergone marked reduction in the direction 

 of the type found in the Gymnosperms. 



