cells 5-7/x in diameter, 7-13-(14)/x long, not constricted or granular 

 at the cross walls; cell contents bright blue-green. 



On moist soil at margins of lakes; tychoplanktonic. Mich., Wis. 



Microcoleus vaginatus (Vauch.) Gomont 1890, p. 353 



PI. 131, Fig. 2 



Plants solitary or, more often, forming dark green and shiny hori- 

 zontal layers; twisted and branched. Sheath colorless and either 

 cylindrical throughout or irregularly undulate and wiinkled; not 

 stained by chlor-zinc-iodide reagent; agglutinated and either open 

 at the end or closed and diffluent. Trichomes numerous within the 

 sheath; not constricted at the cross walls, which are often granular; 

 tapering slightly and briefly at the apex, which is straight. Apical 

 cell capitate, with a calyptra. Cells 3.5-7/x in diameter, i^-2 times 

 as long as wide. 



Mich. 



SCHIZOTHRIX Kuetzing 1843, p. 230 

 Plant mass consisting of several to many trichomes inclosed by a 

 copious sheath of mucilage, which is usually firm and not sticky, 

 the sheath colorless or yellowed, especially in age, frequently forked 

 towards the ends with but a single trichome in the ultimate divisions; 

 filaments either single, in fascicled tufts, or in an expanded layer; 

 trichomes twisted and intertwined, cylindrical throughout but with 

 the apical cell tapering to a blunt or sharp point; cells cylindrical, 

 or shorter than wide, sometimes constiicted at the cross walls. 



This genus should be compared with some species of Phormidium 

 in which the sheaths are agglutinated and difiluent. 



Key to the Species 

 1 . Sheaths colored 2 



1. Sheaths colorless 3 



2. Trichomes 2.8-3/Lt in diameter, not tapering 



at the apices, the end bluntly rounded S. fuscescens 



2. Trichomes 6-13/i in diameter, tapering shghtly toward the 



apices, the end conically rounded S. Muelleri 



3. Filaments compactly agglutinated to form erect tufts S. Friesii 



3. Filaments not agglutinated to form erect tufts 4 



4. Filaments branching but very little, 



united to form horizontal layers S. lardacea 



4. Filaments forming cushion-like masses, or 



penicillate, streaming tufts — ^ 



5. Trichomes 5-1 1/n in diameter. S. rivularis 



5. Trichomes narrower 6 



[506] 



