THE ALGAE 



99 



At the time of fertilization (Fig. 8i) the oosphere exudes a droplet of gelatinous 

 cytoplasm through the pore in the oogonium wall, and the antherozoids 

 accumulate in numbers around the droplet. Several antherozoids may enter 

 the oogonium, but only one enters the oosphere. The small male nucleus 

 migrates to that of the oosphere, which is considerably larger, but does not 

 immediately fuse with it. Whilst lying side by side the male nucleus 



ANTHEROZOIDS 



Fig. 8o. — Vaucheria sessilis. Development of the antheridium. 

 A, Young stage. B, Differentiation of antherozoids. {After 

 Oltmanns.) 



Fig. 8i. — Vaucheria sp. Reproductive branches with 

 lateral antheridia and terminal oogonia. 



increases in size, and when its volume equals that of the female nucleus 

 the two fuse together. 



After fertilization a membrane develops across the oogonial aperture, 

 and subsequently a thick, several-layered envelope is formed around the 

 zygote, thus producing an oospore. At the same time the oil globules unite 

 to form one or more large central globules, and the zygote enters a resting 



