THE ALGJR. 



91 



cells that develop near the upper ends of the branches. 

 When ripe, the cells split almost entirely across, the two 

 portions bend apart, and the zoospore, which has a number 

 of flagella at its smaller and colorless end, swims out. 

 After a period of activity, the zoospore becomes encysted 

 and attaches itself to some fixed object by its smaller end, 

 which becomes disk-shaped and acts as a sucker. The 

 larger end then grows by 

 the usual process of cell 

 division into a new plant. 

 (See Fig. 49.) 



The zoospores of some 

 species develop in another 

 way. These zoospores, 

 which are smaller than the 

 common ones, affix them- 

 selves by their disk-shaped 

 ends to filaments bearing 

 oogonia. Here they de- 

 velop into filaments of a 

 few cells, the end cell be- 

 coming an antheridium, 

 which liberates anthero- 

 zoids to fertilize the eggs 

 in the oogonia. 



In the sexual reproduc- 

 tion the OOgOnia develop FIG. 50. (Edogonium. 



as enlarged cells at inter- 

 vals on the filament. The 

 antheridia develop in other cells on the same or on an- 

 other filament. Flagellated antherozoids, set free from 

 the antheridia, find their way to the ripened egg cells, de- 

 veloped in the oogonia, and fertilize them. The oospore 

 thus formed develops a thick reddish-brown wall and be- 

 comes a resting spore, which ultimately develops into a 



a, filament; 6, 

 showing oogonium ; c, showing oogo- 

 nium and resting spore. Magnified. 



