HOW TO KNOW THE FRESH-WATER ALGAE 



92a (88) Cells spherical or polygonal, arranged to form hollow, spheri- 

 cal or many-sided colonies; cells adjoined by interconnecting pro- 

 tuberances of the mucilaginous sheath. Fig. 77. . . .COELASTRUM 



Fig. 77 a, Coelastium cambiicum 

 Archer (Redrawn from Smith); b, 

 C. microporum Naegeli. 



As the name suggests, cells of 

 this plant are arranged to form a 

 hollow colony. Six or seven spe- 

 cies are known from this country, 

 differing in the shape of the cell 

 and in the length of the intercon- 

 necting processes. Common in both euplankton and in the tycho- 

 plankton. 



Figure 77 



92b Cells not forming hollow colonies and not so adjoined 



93 



93a Cells fusiform, radiating from a common center. Fig. 78 



ACT1NASTRUM 



Fig. 78. Actinastrum Hantzschii Lag. 



These "cigar"-shaped cells are arranged 

 in radiating colonies. This species is more 

 common in the plankton than is A. gracil- 

 limum G. M. Smith which has pointed 

 rather than truncate apices. 



Figure 78 

 93b Cells shaped otherwise, not forming a colony of radiating cells . . 94 



94a Cells ellipsoid to fusiform, adjoined end to end. forming chain-like 

 series. See Fig. 65 DACTYLOCOCCUS 



94b Cells not forming chains 95 



95a Cells ovoid, ellipsoid or fusiform, adjoined by their lateral wall to 

 form a row of 4 in a single series, or a double series in which the 

 cells are alternating. See Fig. 74 SCENEDESMUS 



58 



