180 GUIDE TO THE STUDY OF LICHENS. 



no trouble in recognizing the more typical representa- 

 tives. The dark-blue to almost black gelatinous 

 (when moist) thin thallus is characteristic ; these 

 general characteristics, however, also apply to Lepto- 

 gium. Upon a microscopical examination it is found 

 that no cortical structure is present in Collema. The 

 algae {Nostoc) and hyphae are loosely intermingled. 

 The margin of the thallus is more or less divided or 

 lobed. 



The apothecia are small to medium in size, discoid, 

 sessile upon the thallus. Disk concave, flattened or 

 slightly convex, usually brown or reddish-brown. 



The spore-characters are very variable. They may 

 be simple, two to many-celled and multilocular. Upon 

 further careful study it will no doubt be possible to 

 subdivide the genus upon its spore-differences. Usually 

 the spores are colorless ; faintly colored spores, how- 

 ever, occur. 



The Collemas occur upon soil, bark, rock, and are 

 even found partially or wholly submerged in water. 

 They seem to be somewhat western in their raia^e ; they 

 are, however, also common sooth and east. 



1. Collema pycnocarpiim. Thallus medium, ascend- 

 ing lobes divided and narrowed ; from yellowish-brown 

 at the base to dark-blue green above. Apothecia very 

 numerous, terminal and marginal margin not elevated. 

 Disk convex, reddish-brown to dark-brown. Spores 

 two-celled, colorless, elliptical, 13.5/x X 6.5/x,. 



2. Collema cyrtaspis. Thallus much as in C. pycno- 

 carpum, larger and darker in color. Apothecia some- 

 what larger, crenate margin raised above the flattened 



