cross walls. Chloroplast an irregularly folded plate, about Yo the 

 length of the cell, with 1 pyrenoid. Cells 7.5-10^ in diameter, 10-15/x 

 long. 



Common in many lakes and ponds, both the eutrophic and the 

 soft water types. Mich., Wis. 



Ulothrix tenuissima Kuetzing 1833, p. 518 

 PI. 67, Figs. 11, 12 



Filaments long, composed of cylindrical cells that are shorter than 

 wide, 16-20/A in diameter, thin- walled and not constricted at the 

 cross walls. Chloroplast a broad band encircling about % of the 

 circumference of the cell, with 2 or several pyrenoids. 



Mich. 



Ulothrix variabilis Kuetzing 1849, p. 346 

 PI. 6, Fig. 13 

 Filaments long, slender, and entangled, forming cottony masses. 

 Cells cylindrical, without constrictions at the cross walls. Chloro- 

 plast a folded, parietal plate, 14 to % the length of the cell, with 1 

 pyrenoid (or 2 ?). Cells 4.5— 6;u, in diameter and up to IS/x long. 



Common in a variety of lakes and in seeps along sandy shores; 

 often forming bright green, slimy masses in trickles from springs. 

 Mich., Wis. 



Ulothrix zonata (Weber & Mohr) Kuetzing 1833, p. 517 



PI. 6, Fig. 14 



Filaments attached, usually long and stout, variable in diameter 

 in the same plant mass. Cells short , or elongate-cylindric, sometimes 

 slightly swollen, with constrictions at the cross walls. Cell walls 

 thick, especially near the base of the filament. Chloroplast a com- 

 plete circular band in the midregion of the cell, with several pyre- 

 noids. Cells 20-45/x in diameter, 21-60/x long. 



Not uncommon in several lakes in early summer; frequently 

 found in cold streams, artificial ponds, and in drinking troughs in 

 which there is running water, especially in spring. Mich., Wis. 



HORMIDIUM Kuetzing 1843, p. 244; emend. Klebs 1896, p. 326 



Simple filaments of cylindrical, undifferentiated cells. Chloroplast 

 a parietal plate extending around the cell for y^ or less of the cir- 

 cumference; 1 elongated or oval pyrenoid. Filament readily frag- 

 menting to form Stichococcus-\ike sections. 



[97] 



