the mucilage of aquatic species of Nostoc which occur intermingled 

 among other algae. Wis. 



Plectonema notatum Schmidle 1902a, p. 84 

 PI. 126, Figs. 6, 7 



Free-living, solitary or forming thin mucous wefts; cells cylindric, 

 little if at all constricted at the cross walls, which are marked by 2 

 conspicuous but small granules, 1.2-2/a in diameter, 2-Sfx long; 

 sheath thin but definite; branches solitary or in pairs; filaments 

 1.7-2/i, in diameter. 



Forming a weft on filamentous algae such as Microspora and 

 Rhizoclonium and on sheathed blue-green algae such as Lyngbya 

 and Tolypothrix. Wis. 



Plectonema purpureum Gomont 1892a, p. 101 

 PI. 126, Fig. 8 

 A much-branched filament, united in bundles or forming slimy, 

 reddish or purplish patches; branches solitary or in pairs, much 

 bent and recurving; cells short-cylindric, or disc-shaped, slightly 

 constricted at the cross walls, 3.5-3.8^ in diameter, 2.8-3.5/x long; 

 apical cell broadly rounded; sheath thin but definite; filaments 

 3.7-4/i, in diameter. 



Growing on filamentous algae and on debris in shallow water. Wis. 



Plectonema tenue Thuret 1875, p. 380 

 PL 126, Fig. 9 



A much-branched, thickly-sheathed trichome, forming wooly 

 masses ( sometimes only a few filaments together ) ; cells disc-shaped 

 or quadrate, a little shorter than wide, not constricted at the cross 

 walls, or very rarely so, 6-7.6- ( 10 )/* in diameter, 2-6/* long; apical 

 cell slightly tapering; sheaths thick, colorless at first, becoming 

 yellow and lamellate; branches solitary or in pairs; filaments up to 

 16.6fj. in diameter. 



Among other algae in tychoplankton. Wis. 



Plectonema Wollei Farlow 1877, p. 77 

 PI. 127, Fig. 1 

 A coarse, sparsely branched filament, forming brown or gray- 

 green wooly mats; cells disc-shaped, much shorter than wide, not 

 constricted at the cross walls, 28-50/a in diameter, 4-9/a long; apical 

 cell broadly or truncately rounded; sheaths thick and lamellate; 

 colorless at first but becoming discolored in age; trichomes straight, 

 frequently constricted or interrupted to form hormogonia; branches 



[540] 



