in the tube; globose; median spore wall brown and pitted; 35-50/x 

 in diameter. 



Rare in a few lakes; forming floating masses among larger vege- 

 tation or entangled about the culms of rushes in shallow water, 

 Mich., Wis. 



Zijgnema stellinum (Vauch.) C. A. Agardh 1824, p. 77 

 Filaments forming green, mucilaginous masses, floating free or 

 sometimes in pooled seeps on banks; vegetative cells (25)-28-36- 

 (40)/i, in diameter, quadrate or up to 3 times the diameter in length 

 (mostly about 70/x); fertile cells not inflated. Zygospores formed in 

 one of the gametangia; broadly ovate or oblong; median layer brown 

 and deeply pitted; 30-35/i, in diameter, 35-48/x long. 

 In Sphagnum bogs and sloughs. Mich., Wis. 



Zijgnema sterile Transeau in Transeau, 

 Tiffany, Taft, & Li 1934, p. 212 



Filaments scattered among other algae and seldom forming pure 

 masses; vegetative cells 44-54/* in diameter, 22-69/x long, with a 

 thick wall and inclosed by a firm pectic sheath which may be as 

 much as 15/x in thickness, the sheath often deeply constricted at the 

 plane of the cross walls; cell contents very dense and so nearly 

 opaque that the individual chloroplasts can scarcely be discerned. 

 Conjugation not known; reproduction by thick-walled, scrobiculate 

 akinetes which fill the cell when mature. 



Common; intermingled with other algae in shallow water, espe- 

 cially in small lakes and ponds where there is a high concentration 

 of decomposing organic matter. Mich., Wis. 



Zijgnema sijnadelphum Skuja 1926, p. 110 

 PI. 74, Fig. 1 

 Vegetative cells 17-21;u in diameter; fertile cells not inflated 

 Zygospores formed in the tube; globose, or compressed parallel with 

 the conjugation tube; median layer blue and scrobiculate; 33-36^ 

 in diameter. 

 Mich. 



ZYGNEMOPSIS (Skuja) Transeau 1934, p. 203 



Filaments slender, composed usually of cylindrical cells which 

 are as much as 10 times their diameter in length; chloroplasts 2 

 stellate or cushion-like masses, containing a single pyrenoid each. 

 Conjugation scalariform (between dissociated cells in some species 

 ?), the gametangia persisting and becoming filled with cellulose- 



[ 326] 



