HOW TO KNOW THE FRESH-WATER ALGAE 

 54b Cells other shapes 56 



55a Chloroplast axial with one to several pyrenoids. Fig. 46 



MESOTAEN1UM 



Figure 46 



Fig. 46. Mesotaenium Greyii Turner (forma), show- 

 ing variation in cell shape. 



These oval or oblong cells have an axial, plate- 

 like chloroplast and a wall that is all in one piece 

 (Saccoderm desmids). Although some of the 5 or 6 

 species occurring in the country are free-floating, 

 others (Mesotaenium macrococcum (Kuetz.) Roy and 

 Biss., e.g.) usually occur among mosses and in vari- 

 ous swamp situations. In high mountain seeps they 

 may occur as gelatinous masses on rocks. 



55b Chloroplast a parietal plate, without a pyrenoid. See Fig. 39 



COCCOMYXA 



56a Colony forming stringy, intestiniiorm masses, sometimes perfor- 

 ated skeins. See Fig. 35a TETRASPORA 



56b Colony shaped otherwise 57 



57a Colony a few (2-4) oval cells inclosed in an irregularly shaped, 

 layered, gelatinous sheath. Fig. 47 DACTYLOTHECE 





'. 



Figure 47 



Fig. 47. Dactylothece sp. 



Cells in this genus are shaped as in Mesotae- 

 nium (Fig. 46) but they are much smaller (not more 

 \ than 3 p in diameter) and have a laminate, pari- 

 etal chloroplast. The cells are inclosed in mu- 

 cilage and form thin expanded masses on moist 

 rocks. D. confluens (Kuetz.) Hansg. is the only 

 species reported from North America. 



44 



