No. IO.] FRESH- WATER ALG^E. 49 



Key to Genera. 

 Filaments attached; chromatophore a homogeneous 



zonate band, with one to several pyrenoids. . . Ulothrix* 

 Filaments not attached; chromatophore a parietal 



disk or plate, with one pyrenoid Stichococcus* 



Filaments generally not attached; chromatophore 

 granular, covering more or less completely the 

 whole cell wall, containing starch but no pyrenoids 



Microspora* 

 Description of Genera. 



Ulothrix Kutz. (Hormiscia, as used by Rabenhorst, 

 Hansgirg, and De Toni). Filaments simple; each cell except 

 the basal cell capable of reproduction. The chloroplast is 

 parietal with one or many pyrenoids. Asexual reproduction by 

 zoospores. Sexual reproduction by conjugation of gametes, 

 of which eight or more may be formed in a cell. 



U. zonata (Web. and Mohr) Kutz., Fig. 94. 



U. tenerrima Kutz., Fig. 93. 



Figures 86 to 91 are specimens of Ulothrix of which we 

 have not determined the species. 



[U. implexa Kutz. ; U. flacca (Dillw.) Thur.] 



Stichococcus Nag. (Hormococcus Chodat). Very like 

 Ulothrix, but unlike it in being almost wholly aerial, and in 

 the fact that the filaments easily and commonly dissociate into 

 cylindrical cells or small groups. The dissociation frequently 

 occurs first on the one side and then on the other, giving a 

 zig-zag appearance. Each cell has a parietal chloroplast, 

 usually occupying a part of the cell wall and containing a 

 small pyrenoid. Propagation by cell division, breaking up of 

 the filaments, by non-motile spores, and by biciliated zoogonidia. 



6". Uaccidas (Kutz.) Gay, found but not figured. 



[S. rivularis (Kutz.) Haz.] 



Microspora Thur. Filaments composed of cylindrical 

 or slightly swollen cells. The firm, sometimes lamellose cell 

 walls occasionally break up into H-shaped pieces, each piece 

 composed of a transverse wall and portions of the lateral walls 

 of the two adjoining cells. The cells are uninucleate, and a 

 more or less reticulated chloroplast occupies the cell wall. 

 4 



