HOW TO KNOW THE FRESH-WATER ALGAE 



Figure 86 



110a With 2 axial chloroplasts bearing longitudinal ridges, a chlorc- 

 plast in either horn of the cell; pyrenoids conspicuous, usually in 

 an axial row. Fig. 86 CLOSTER1UM 



Fig. 86. Closterium spp. Two of the 

 many variations in curvature and 

 cell proportions exhibited in this 

 genus. 



This desmid usually has distinct- 

 ly crescent-shaped cells, but some 

 species are nearly straight, or have 

 the outer margin of the cell bowed 

 and the inner almost straight. A few 

 species have the poles extended to 

 form long, almost straight, needle-like processes which are swollen at 

 the tip. Although this genus does not show the constriction of the cell 

 to form two semi-cells characteristic of most other true desmids, the 

 cell contents are symmetrically divided into 2 portions with the nucleus 

 centrally located. A never-failing characteristic of Closterium is the 

 polar vacuoles containing vibrating granules of gypsum. 



110b Cells with 1 chloroplast, or with parietal chloroplasts not arranged 

 as above HI 



Ilia Cells only slightly crescent-shaped, (usually straight or nearly so, 

 and often irregularly curved), with poles drawn out into fine 

 points 112 



111b Cells definitely crescent-shaped, or with poles not drawn out into, 

 fine points " *" 



112a Cells attached by a slender stipe to other algae or to microfauna. 

 Fig. 87 CHARAC1UM 



Fig. 87. a, Characium D e b a r y a n u m 

 (Reinsch) DeToni; b, C. ornithocephalum 

 A. Braun; c, C. rostratum Reinhard. 

 There are numerous species in this 

 genus, differentiated by shape of cell and 

 by presence or absence of a stalk. Some 

 are very minute and are easily overlooked, 

 whereas others are larger and grow in as- 

 sociations so as to form conspicuous patch- 

 es on filaments of algae or on small 

 animals. The genus Characiopsis contains species shaped like some 

 of those of Characium and care should be used in determining the 

 color of the chloroplast and the presence or absence of a pyrenoid 

 in making identification. Characiopsis (Fig. 217) has a yellow pigment 

 predominating and starch tests are negative; is a member of the 

 Chrysophyta. 

 1 12b Cells not attached by a stipe . . ; 113 



Figure 87 



63 



