DESMIDS. 



115 



The sliminess in which many of the desmids are 

 invested usually serves the purpose of keeping the 

 loosely aggregated cells together, as in the species 

 just mentioned, whose generic name is derived from 

 this glassy sheath. But although these colonies of 



Fig. 69. 



Fig. 70. 







Euastrum oblongum. (Front view) x 250. 



Hyalotheca dissiliens. 



desmids are far from uncommon, they are not so 

 abundant as the single-celled species. The latter 

 may nearly always be seen in the act of dividing 

 themselves into two halves their only method of 

 reproduction. 



Among these the genera Cosmarium, Micrasterias, 

 Closterium, and Euastrum are usually abundant, and 

 the student may readily obtain and keep them 



I 2 



