CHLOROPHYCE.E 



169 



motionless spores within large sporangia. These spores, 

 which are round and provided with a membrane, do 

 not germinate in the ordinary way but become them- 

 selves small plantlets with a rhizoid attachment. 

 These either soon give rise to a filamentous thallus, 

 or, becoming enlarged, are transformed into new 

 sporangia, the actual outcome of which has not yet 

 been observed. 



In Urospora and Rhizoclonium there is a method of 

 vegetative propagation by the separation of vegetative 

 cells densely packed with con- 

 tents. In Urospora the filament 

 breaks up first into multicellular 

 parts and eventually into single 

 cells. These either germinate 

 directly or, after surrounding 

 themselves with thick walls and 

 resting, produce zoospores. In 

 Ehizodonium the process is sim- 

 ply that of the cells becoming 

 rounded and dropping off; they 

 germinate by the production of a 

 filament in all cases. 



The Geographical Distribution. 

 Gladoplwra has a world-wide 

 distribution in both salt and 

 fresh water. Clwetomorplia is 

 also extensively distributed, but 

 mostly in the sea. Rhizocloniiim 

 has a similar distribution to 

 Cladophora. All three genera 

 are represented by numerous species, many of them 



FIG. 52. Chcetomorpha 

 Darwini (reduced). 



