POscillatoria lacustris ( Kleb. ) Geitler 1925a, p. 362 



[Trichodesmium lacustre Klebahn 1895, p. 13] 



PI. 109, Fig. 15 



Trichomes straight, lying parallel in free-floating, flake-like bun- 

 dles or fascicles, not tapering at the apices; apical cell broadly 

 rounded, without a calyptra; cells compressed globose or barrel- 

 shaped, sometimes semiquadrate, or a little longer or shorter than 

 wide, 5-7^ in diameter, 3-7/a long; cell contents with many pseudo- 

 vacuoles. 



The specimens assigned here are enigmatic. The bundles of 

 trichomes stiongly suggest Trichodesmium because of their arrange- 

 ment and lack of heterocysts. They are not like Trichodesmium 

 lacustre Klebahn, however, in respect to the morphology of the 

 apical cell which in that species is long and attenuate, but which 

 in our specimens is short and rotund. The suggestion has been made 

 that the plant found in our collections is a juvenile form of Aphani- 

 zomenon, which would appear reasonable because of the similarity 

 in respect to trichome arrangement, cell shape, and cytology. As I 

 have pointed out elsewhere ( 1942, p. 665 ) , however, the occurrence 

 of these bundles of trichomes in what certainly appears to be a 

 mature condition and without any suggestion of nostochaceous 

 characters (heterocysts, gonidia), precludes such a disposition. 

 Geitler has assigned Klebahn's species to Oscillatoria and relegates 

 the Wisconsin plant previously reported by Smith ( 1920 ) to Aphani- 

 zomenon. There is scarcely enough evidence at present to justify 

 giving a new name to the Wisconsin plant, but it is possible that 

 subsequent study will establish it as a new fresh-water species of 

 Trichodesmium. 



Plankter; in hard or semi-hard water, especially eutrophic, lakes. 

 Wis. 



Oscillatoria limnetica Lemmermann 1900, Ber. d. Deutsch. 



Bot. Ges., 18, p. 310 

 PL 109, Fig. 16 



Trichomes solitary and planktonic or intermingled with other 

 algae in littoral waters; straight or flexuous, not tapering toward the 

 apex. Apical cell bluntly rounded and without a calyptra. Cells 

 1.5-1.8;a in diameter, 3% times the diameter in length; not con- 

 stricted at the cross walls, which are scarcely visible and are not 

 marked by granules. 



In shallow water of swamps and bogs; among submerged aquatics. 

 Wis. 



[488] 



