THE GKEAT GROUPS OF ALG^E 



25 



about itself. This firm wall indicates that the oospore is 

 not to germinate immediately, but is to pass into a resting 

 condition. Spores which form heavy walls and pass into 

 the resting con- 

 dition are often 

 spoken of as " rest- 

 ing spores," and it 

 is very common 

 for the zygotes 

 and oospores to 

 be resting spores. 

 These resting 

 spores enable the 

 plant to endure 

 through unfavor- 

 able conditions, 

 such as failure of 

 food supply, cold, 

 drought, etc. 

 W hen favorable 

 conditions return, 

 the protected rest- 

 ing spore is ready 

 for germination. 



When the 

 oospore of Edogo- 

 nium germinates 



it does not develop directly into a new filament, but the 

 contents become organized into four zoospores (Fig. 7, F), 

 which escape, and each zoospore develops a filament. In 

 this way each oospore may give rise to four filaments. 



It is evident that Edogonium is a heterogamous plant, 

 and is another one of the Conferva forms. Conferva bodies 

 are not always simple filaments, as are those of Ulothrix 

 and Edogonium, but they are sometimes extensively branch- 

 ing filaments, as in Cladopliora, a green alga very common 



FIG. 8. Cladophora, a branching green alga, a very 

 small part of the plant being shown. The branches 

 arise at the upper ends of cells, and the cells are 

 c oen ocy tic . C ALD WELL . 



