somewhat irregular, Trichomes relatively loosely entangled in a 

 colorless mucilage. Cells globose, (4.5)-5-8/a in diameter; frequently 

 not adjoined but loosely arranged in a series. Heterocysts subspher- 

 ical or ovate, 7.3jLt in diameter. Gonidia ovate or subspherical, 6-7/u, 

 in diameter, 10-15/i, long; with smooth walls. Colony 1-9 mm. in 

 diameter. 



Subaerial or growing on pebbles in running water or floating 

 and entangled among filamentous algae; common. 



Mich., Wis. 



Nostoc muscorum C. A. Agardh 1812, p. 44 

 PI. 120, Fig. 6 



Colony a brown, lumpy or tuberculose membrane, firm and 

 leathery when growing on moist soil. Trichomes crowded and much 

 entangled. Cells variable in shape, subcylindrical, barrel-shaped, or 

 subglobose; constricted at the cross walls; 3-4/i, in diameter, 5.4-6.5ju, 

 long, Heterocysts globose or compressed-globose, 6-7/i, in diameter. 

 Gonidia ovate, in a series, with smooth ochraceous membranes. 



Occurring in swamps and in shallow water of lakes, mostly soft 

 water; common. Mich., Wis, 



Nostoc paludosum Kuetzing 1850, p. 1 

 PI. 121, Figs. 1-3 



Plant a minute, oblong or subspherical colony in which a few 

 trichomes are loosely or (when young) tightly coiled in a wide and 

 copious gelatinous investment. Cells barrel-shaped, 3-4jLt in diameter; 

 cell contents yellowish or olive-green. Heterocysts ovate, 4-5/x in 

 diameter, 6/i, long. Gonidia ovate, in short series; with a smooth 

 membrane; 4-4.5/t in diameter, 6-8/i, long. Colony 1 mm. or less in 

 diameter. 



In ditches and Sphagnum bogs; caught among mosses and mats 

 of filamentous algae. Wis. 



Nostoc pruniforme C. A. Agardh 1812, p. 45 

 PI. 120, Figs. 7, 8 



A spherical or ovate colony of loosely entangled or sometimes 

 radiating trichomes inclosed in a copious and firm gelatinous matrix; 

 olive-green when young and changing to a black-olive in age. Cells 

 spherical or compressed-spherical to barrel-shaped; 4-6- (7.5) /a in 

 diameter, 4-7/a long; cell contents blue-green or gray-green. Hetero- 

 cysts globose or compressed-globose, 6-7ju, in diameter. Gonidia 

 spherical, about 10/x in diameter. 



This species is common in hard water lakes and slow-flowing 



[524] 



