HOW TO KNOW THE FRESH-WATER ALGAE 



the female gametangium (oogonium). Oedogonium plants begin as 

 attached filaments and may remain so throughout life, or they may 

 become free-floating and form cottony masses near the surface, usually 

 becoming pale yellow-green or cream-colored in age. Often these 

 masses are so dense that if left to dry by the evaporation of water in 

 which they are growing they form what is known as "algae paper." 



225a (223) Chloroplast a parietal plate, a ring, or a band which in- 

 completely encircles the cell 226 



225b Chloroplast massive and dense (dif- 

 ficult of determination), or a parietal 

 sheet of thick and thin areas (padded 

 appearance), or a branched, beaded 

 thread (see MicTospora). Fig. 159 V2. 

 237 



Figure 159% 



226a Filaments composed of long, cylindrical, multinucleate units; 

 chloroplasts in the form of several parietal rings in each unit. 

 Fig. 160 SPHAEROPLEA 



Fig. 160. Sphaeroplea an- 

 nulina (Roth) Ag.; a, 

 vegetative cell with 

 ring - like chloroplasts, 

 and b, one cell con- 

 taining fertilized eggs. 



Two species of this 

 genus are known from 

 the United States, but S. 

 annulina is the one most 

 frequently seen, although it actually is a rather rare plant. Wherever 

 it occurs it is likely to be in abundance. The characteristic long, cylin- 

 drical 'cells' may be mistaken for species of Rhizoclonium (Fig. 158), 

 especially in the examination of preserved material. It is to be ex- 

 pected in shallow water of marshes and in bays of lakes. 



Figure 160 



226b Filaments not composed of long, multinucleate units; chloroplasts 

 otherwise, usually 1 in each cell 227 



103 



