28 BRITISH DESMIDIACE^;. 



+ + Cells from the vertical view commonly radia- 

 ting ; triangular, quadrangular, or up to 11- 

 radiate ; rarely fusiform. 



Staiirastriiui. 



'' After division the cells remain attached to form colonies. 

 t Colonies spheroidal ; cells not in contact, but joined 

 together bv gelatinous bands. 



O ^ o 



t Gelatinous bands narrow ; few cells forming a 

 microscopic colony. 



Cosmocladium. 



tt Gelatinous bands very broad; many cells forming 

 a macroscopic colony. 



Oocardium. 

 tt Colonies thread-like; cells attached by their apices 



into long filaments. 



t Cells attached by special apical processes. 

 Apical processes very short. 



Sphserozosma. 



Apical processes long and overlapping the 

 apex of the adjoining cell. 



Oinjchonema. 



tt Apices of cells plane and flat. 

 Cells deeply constricted. 



| Cells in vertical view elliptical. 



Spondylosium. 



|| || Cells in vertical view quadrangular with 

 produced angles. 



Pkt/matudocis. 

 Cells very slightly constricted. 



Hyalotheca. 



b. The obliquely-fitting new and old portions of the cell-wall at 

 the point of division (the isthmus) develope a girdle-like thickening, 

 which projects back into each of the old semicells during division. 

 Cells attached to form thread-like colonies. 



;; Cells joined by special apical processes. 



Streptonema. 



** Cells joined by their flat apices or by flattened apical pro- 

 jections. 



t Cells short ; fusiform, triangular or quadrangular 

 (rarely circular) in vertical view. 



Desmiditint. 

 tt Cells elongate, cylindrical. 



Gymnozyga. 



