diameter, 3-4^ long; either adjoined or separated ( in different parts 

 of the colony). Heterocysts spherical, 6ju, in diameter. Gonidia not 

 observed ( unknown ? ) . 

 Tychoplankter; also found on bottom in shallow water. Mich., Wis. 



Nostoc commune Vaucher 1903, p. 222 

 PI. 119, Fig. 13 



Plant at first a brown, globular, firm, gelatinous mass, later, 

 especially when growing on moist soil, becoming expanded; lobed 

 and clathrate; forming tough leathery layers of considerable extent 

 (20 cm. wide). Trichomes closely entangled and intertwined, espe- 

 cially compact in the outer, brown, layer, less so in the colorless, 

 softer, inner region of the colony. Cells subglobose or barrel-shaped 

 4-6/x in diameter, Ifi long; constricted at the cross walls. Heterocysts 

 frequent, spherical, 7-8.4/x in diameter. Gonidia the same shape and 

 about the same size as the vegetative cells. 



On the bottom and on submerged objects; collected from depth of 

 20 feet in soft water lakes; on damp soil at the margin of lakes and 

 swamps. Mich., Wis. 



Nostoc ellipsosporum (Desmaz.) Rabenhorst 1865, Vol. 2, p. 169 

 Plant mass reddish-brown, irregularly globular. Trichomes loosely 

 entangled. Cells subcylindric to cylindric; 4ix in diameter, 6-14ju, 

 long; constricted at the cross walls, which are truncate; cell contents 

 yellowish or olive. Heterocysts subglobose or oblong, 6-7/x in diam- 

 eter, 6-l4fji long. Gonidia ellipsoid or cylindric-oblong; 6-8/a in 

 diameter, 14-19|U, long; with smooth walls. 



On grass at margin of lakes; on clay banks. Mich. 



Nostoc Linckia (Roth) Hornet & Thuret 1880, p. 86 

 PL 119, Figs. 14-16 



Colonies firm and globular when young, becoming irregularly 

 expanded, clathrate, and membranous, soft in age; blue-green in 

 color, becoming dirty green. Trichomes much entangled, twisted. 

 Cells subglobose or barrel-shaped, 3-4.5;ii in diameter. Heterocysts 

 subspherical to ovate, 6-7.5ix in diameter. Gonidia subglobose; 

 6— 7/i, in diameter, 7—Six long; with dark, smooth membrane. 



Among clots of filamentous algae in hard water lakes; sometimes 

 on moist earth at margin of lakes. Mich., Wis. 



Nostoc microscopicum Carmichael {see Harvey in Hooker 1833, p. 399) 



PI. 120, Figs. 3-5 

 Colonies minute, blue-green or olive-green, globose or ovoid to 



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