268 



COLLEGE BOTANY 



niing for a time come to rest and grow into new filaments. Some- 

 times very small biciliate zoospores (gametes) are formed which 

 fuse and produce zygospores, which in turn give rise to a genera- 

 tion of zoospores which grow into new plants. 



(Edogonium (Fig. 122, f-h) is a very common filamentous 

 heterogamous form. The plants are anchored to stones or sticks 

 and each cell is uninucleate. Some cells produce large, usually 

 solitary, zoospores bearing a crown of cilia and having the power 

 to grow into new plants. Other cells form large oogonia, each 

 containing a single egg or oosphere, while still other small cells 

 produce one or more sperms. The sperms escape and swim, 



b c d 



FIG. 121. (a to e) Ulothrix; (/to h) (Edogonium. 



some of them reaching the oogonia, which they enter through a 

 small opening and fuse with the egg or oosphere. 



In certain other species the oogonia and antheridia may be 

 produced on different filaments and are therefore dioecious. The 

 female plants are large and are produced from large zoospores. 

 The male plants are small and are produced from small zoospores 

 (androspores), which are somewhat larger than sperms. These 

 small male plants are frequently attached to the female plants 

 and the terminal cells develop into antheridia. 



C oleoclicete is a small plate-like body composed of many cells 

 and is usually found attached to water plants. Although small, 

 it has a comparatively complex structure. It reproduces by 

 means of zoospores and heterogamous gametes. 



The order Siphonales is composed of species which are fila- 

 mentous and with few or no septa. Although they may be con- 

 sidered unicellular they are multinuclear. A plant body of 



