THALLOPHYTA: ALGAE 



47 



Some species of Oedogonium are monoecious, the antheridia and oogonia 

 occurring in the same filament. Other species are dioecious, the two 

 kinds of sex organs being borne on separate filaments. In some dioecious 

 species the male and female filaments are approximately equal in size. 



i^^ 



B 



CD E 



Fig. 34. Reproduction in Ocdoj7ont?/m, X500. ^ and B, the entire fontents of a vegetative 

 cell escaping as a zoospore; C, portion of filament with two groups of antheridia; also a single 

 escaped sperm; D, portion of filament with an oogonium containing a mature egg in which 

 are many pyrenoids and starch grains; E, heavy-walled zygote still within the oogonium; 

 F, group of four zoospores produced by the zygote. {A and B, after Him; F, after Juranyi.) 



In others the male filaments are very small, consisting of only a few cells. 

 These dwarf filaments are produced by special small zoospores, called 

 androspores, that originate singly in rows of small cells resembling 

 antheridia. The androspores germinate on the female filaments near or 

 on an oogonium (Fig. 35). The dwarf filament usually consists of a 

 single vegetative cell that cuts off one or several terminal antheridia, each 

 producing two sperms. Figure 35 shows three dwarf filaments of different 

 ages. In the one on the right the single vegetativ-e cell has cut off a small, 

 undivided, antheridial cell. In the middle filament a second antheridium 



