WISCONSIN PHYTOPLANKTON 53 



thickness as the other cells, with distal end rounded but not capitate. 

 Sheaths firm, hyaline, very narrow, extending for some distance beyond 

 the end of the trichome. Cells cylindrical, at least twice as long as 

 broad. Cell contents homogeneous; generally grey, rarely blue-green 

 in color. (Euplanktont). 



Cells 1-1.5 p, broad, 3-8 p. long. 



Bear (1) (c), Geneva (ss), Soft (rr), Upper Nashotah (rrr). 



The length of the individual cells of Wisconsin specimens exceeds 

 that given by Lemmermann but it is very probable that I am dealing 

 with the same species that he names L. limnetica. Several plankton 

 "species" have been described which are closely related and it is very 

 probable that future investigations will show that all of these straight, 

 very narrow, colorless "species" should be included under one collect- 

 ive specific name. 



LYNGBYA CONTORTA Lemmermann. PL 7, Figs. 12-13. 



Forschungsbr. a. d. Biol. Stat. zu Plon 6: 202, pi. 5, figs. 10-13. 1898; G. S. 

 West Jour, of Bot. 47: 246, pi. 498, figs. 5 A -5 B . 1909. 



Filaments free-floating, solitary; occasionally straight, generally 

 twisted to form regular, loose or compact spirals or helices. Sheaths 

 firm, very thin, extending for some distance beyond the trichomes. Trich- 

 omes the same thickness throughout, not constricted at the cross walls, 

 apical cells rounded but not capitate at the distal ends. Cell contents 

 homogeneous, grey to pale blue-green. (Euplanktont). 



Cells 1.5-2 p broad, 3-6 /* long. Spirals 15-20 /*. broad, 6-14 p be- 

 tween the turns. 



Mendota (rr), Pine Tree (ss), Poor Farm (s), White Ash (cc). 



The specific distinction of this species is based in large part upon the 

 spiral twisting of the filament. Since certain normally straight fila- 

 ments of other algae become spirally twisted under limnetic conditions 

 (vide W. & G. S. West, Proc. Roy. Soc. London Ser. B, 81: 169, fig. 1. 

 1909) the validity of spiral twisting as a specific character arises. 

 L. contorta was found in considerable quantity at different stations and 

 the vast majority of filaments were spirally twisted. On the other 

 hand numerous filaments with cells of the same size that showed no 

 signs of twisting were collected from other stations. I think that Lem- 

 mermann is correct in considering these distinct species and that the 

 spiral twisting of filaments in plankton species of the Myxophyceae is 

 a sufficiently constant character to warrant the establishment of species 

 in both this genus and Anabaena. 



