HOW TO KNOW THE FRESH-WATER ALGAE 



95b Cells globular or variously shaped, not attached side by side in 

 one plane 96 



96a Cells fusiform or trapezoidal, attached with their long axes paral- 

 lel about a common center. Fig. 79 TETRADESMUS 



Figure 79 



Fig. 79. Tetradesmus Smithii Presc. 



This plant resembles some Scenedesmus spe- 

 cies (Fig. 74) but differs in having the cells qua- 

 drately arranged rather than in a series in one 

 plane. There are but two species known in this 

 country, both of them from the euplcmkton of 

 Wisconsin lakes. T. wisconsinense G. M. Smith 

 has trapezoidal cells. 



96b Cells some other shape and not attached about a common center . 97 



97a Cells crescent-shaped, in groups of 4, 2 with concave sides toward 

 one another, the other 2 cells in another plane with poles at one 

 end only in juxtaposition. See Fig. 57 TETRALLANTOS 



97b Cells sickle-shaped, fusiform or crescent-shaped, twisted about one 

 another. See Fig. 68 ANKISTRODESMUS 



98a (82) Cells adjoined by gelatinous strands or threads formed from 

 the remains of old mother-cell walls 99 



98b Cells not adjoined by remains of old mother-cell walls 101 



99a Cells spindle-shaped, in clusters of 4-8-16 at the ends of radiating 

 gelatinous stalks. Fig. 80 ? ACTIDESMIUM 



Fig. 80. Actidesmium Hookeri Reinsch. 



This rare plant occurs in the tychoplankton 

 of shallow pools. The star-shaped clusters of 

 cells at the ends of radiating (sometimes dicho- 

 tomously branched) gelatinous stalks render it 

 easy of identification. 



59 



Figure 80 



