HOW TO KNOW THE FRESH-WATER ALGAE 



18a (15) — Colony spheroidal or oval; cells pear-shaped, crowded to- 

 gether with broad ends all directed outwardly. Fig. 14 



PANDORINA 



Fig. 14. Pandoiina morum Bory. Cells are 

 pear-shaped and often are more compact- 

 ly arranged than shown here. 



A tumbling colony in which pear-shaped 

 cells are closely compacted within a spher- 

 oidal or oval gelatinous sheath. Often col- 

 onies are to be seen in which all individuals 

 have divided to form each a daughter colony. 

 There is one other species in the United 

 States, (possibly a Eudorina Fig. 17). 



Figure 14 



18b Colony globular or broadly ovoid; cells not crowded but evenly 

 spaced (even though close together) 19 



19a Colonies large, containing hundreds or thousands of cells. Fig. 

 15 VOLVOX 



Figure 15 



Fig. 15. Volvox tertius Meyen. a. Colony 

 showing only vegetative cells; b, two 

 organisms showing eye-spot. Other 

 species have colonies containing a 

 larger number of cells, and some have 

 intercellular connections. 



This globular colony containing thou- 

 sands of cells is usually easily seen 

 with the unaided eye. It occurs in water 

 that is rich in nitrogenous substances 

 (frequently) and sometimes causes 

 "blooms" of short duration (two or three 

 days during summer months). 



19b Colonies composed of 8-16-64-128 cells 



20 



28 



