HOW TO KNOW THE FRESH-WATER ALGAE 



113a Wall at the poles of the cell extended to form slender setae, one 

 of which may be forked; cholorplasts extending the full length of 

 the cell. Fig. 88 SCHROEDER1A 



Fig. 88. Schroederia Judayi G. M. Smith. 



One of the three species found in the 

 United States, S. setigera (Schrod.) Lemm., 

 is the most common. The cells have 

 a spine at both poles which is undivided, 

 whereas S. ancora G. M. Smith, also fair- 

 ly common in plankton, has one polar 

 process forked at the tip. In a Michigan 

 pond the former species occurred as prac- 

 tically the only member of the plankton 

 throughout winter months. 



Figure 88 



113b Tips of the cells narrowed to fine points at least at one end with 



the poles narrowly rounded, tip not seta-like but narrowly pointed; 



chloroplast not extending the full length of the cell. Fig. 89 ... . 



OUROCOCCUS 



Fig. 89. Ourococcus bicaudatus Grob. (Redrawn 

 from Smith.) 



This rare plant might be confused easily with 

 Ankistrodesmus spp. (Fig. 68) but the cells are 

 usually stouter. It is closely related to Elakato- 

 thrix (Fig. 38) in the Order Tetrasporales be- 

 cause the cells retain the ability to divide vege- 

 tatively to form new individuals, whereas in 

 the Order Chlorococcales, which concerns cells 

 similar in shape to Ourococcus, the cells cannot undergo division but 

 must form new individuals within the wall of the parent cell. 



114a (111) Cells very slender, needle-like or sometimes fusiform (usual- 

 ly in clusters but sometimes solitary), often only slightly, crescent- 

 shaped; chloroplast parietal, the outline often discerned with dif- 

 ficulty. See Fig. 68 ANKISTRODESMUS 



114b Cells stouter, not needle-like; definitely crescent-shaped, the chlo- 

 roplast parietal and definite in outline 115 



64 



