which are scarcely discernible, especially in the anterior end of 

 the trichome; cell contents almost colorless. 



This is the smallest species of Oscillatoria appearing in our col- 

 lections. It is easily mistaken for a filamentous bacterium because 

 of its size and pale color. In mass, however, it clearly shows its 

 blue-green algal identity. Not infrequently this species is found en- 

 tangled in the mucilage of colonial Cyanophyta. 



Tychoplanktonic and euplanktonic. Mich., Wis. 



Oscillatoria articulata Gardner 1927, p. 34 

 [Oscillatoria Grunowiana var, articulata ( Card. ) Drouet] 



PL 107, Fig. 22 

 Trichomes entangled, flexuous, forming a thin blue-green plant 

 mass, or scattered among other algae, not tapering to the apices; 

 apical cell rounded, not capitate and without a calyptra, but with 

 a thickened outer membrane; cells 2.8-3.2;ii in diameter, quadrate 

 or 14-1/3 as long as broad, not constricted at the cross walls; which 

 are conspicuously thickened, sometimes as much as the length of 

 the cell cavity. 



Mich. 



Oscillatoria Bornetii Zukal 1894, p. 260 

 PI. 108, Figs. 19, 20 

 Trichomes forming a slimy, expanded plant mass, or intermingled 

 among other algae; more or less straight but often bent or slightly 

 sigmoid in the apical region, not tapering toward the apex. Apical 

 cell smoothly rounded, not capitate, and without a calyptra. Cells 

 (10)-12-16/i, in diameter, 3.7-4/i long; not constricted at the cross 

 walls; cell contents pale, almost colorless, with large quadrangular 

 alveolations or vacuoles. 



Tychoplankter; in lakes and slowly flowing water. Wis. 



Oscillatoria chalybea Mertens in Jiirgens 1822, Dec. 18, No. 4 



PI. 109, Figs. 8, 9 

 Trichomes aggregated to form a dark blue-green plant mass; 

 straight for a portion of their length but much entangled and some- 

 times spirally twisted, gradually tapering toward the apex. Apical 

 cell conical, with a smooth, unthickened outer membrane. Cells 

 (6)-8-12-(13)/x in diameter, 4-6.8/^ long; shghtly constricted at 

 the cross walls, which are not granular. 

 Tychoplankter. Mich., Wis. 



[486] 



