40. Trichomes tapering at the apex 41 



40. Trichomes not tapering at the apex— ____ O. nigra 



41. Trichomes crooked and undulate at the apex; 



not constricted at the cross walls O. terebriformis 



41. Trichomes curved at the apex, sometimes straight; 



constricted at the cross walls O. formosa 



Oscillatoria acutissima KuflFerath 1914, p. 264 

 PL 109, Fig. 1 



Trichomes solitary and scattered, or loosely entangled in the 

 mucilage of other algae; gradually tapering to the apex, which is 

 curved or bent slightly. Apical cell acute-conical, with a calyptra. 

 Cells 1.5-2/i, in diameter, li^ to 3 times longer than wide; not con- 

 stricted at the cross walls, which are not granular. 



Although I have not seen type specimens of O. acutissima, I have 

 assigned our plants to this species on the basis of their agreement 

 with Kufferath's description. 



Tychoplankter; in mucilage of colonial diatoms and egg masses. 

 Mich., Wis. 



Oscillatoria Agardhii Gomont 1892a, p. 205 

 PI. 108, Figs. 15, 16 



Trichomes interwoven to form a blue-green plant mass; occasion- 

 ally found floating free; straight throughout their entire length, 

 briefly tapering at the anterior end, which is usually capitate, but 

 frequently smooth. Apical cell truncate-conical, with or without a 

 calyptra. Cells (3.4)-5.5-6(U, in diameter and not constricted at the 

 cross walls, which are granular; their length from Yo to approxi- 

 mately equal their width (sometimes 1% times their width in length). 



This species shows a great deal of variation in the morphology 

 of the apex of the trichome. The straight interwoven filaments, the 

 cell proportions, and the granular cross walls help to identify* it. 



Abundant in tychoplankton; generally distributed. Mich., Wis. 



Oscillatoria amoena ( Kuetz. ) Gomont 1892a, p. 225 

 PI. 109, Figs. 2-4 

 Trichomes usually forming a thin, submerged, weft-like, blue- 

 green mass, or sometimes scattered among other algae; usually 

 straight but not rigid, slightly tapering toward the apex. Apical 

 cell broad, capitate, with a cone-shaped calyptra. Cells (2.5)-4-5/x 

 in diameter, 2.5— 4.2/x long; usually slightly constricted at the cross 

 walls, which are granular. 



In tychoplankton of littoral flora; in springs. Mich., Wis. 



[484] 



