WISCONSIN PHJTOPLANKTON 51 



KEY TO THE SPECIES. 



Apex of trichome gradually tapering O. PBOLIFICA 



Apex of trichome not tapering O. TENUIS 



OSCILLATORIA PROLIFICA (Greville) Gomont. PI. 7, Figs. S-5. 



Ann. Scl. Nat. 7 'Ser. Hot. 16: 205, pi. 6, fig. 8. 1892; Olive, Trans. Wis. Acad. 

 Scl., Arts, & Lett. 15 1 : 124-134. 1905; Hyams and Richards, Technology Quart. 

 14: 302-310, figs. 1-8. 1901. 



Filaments rarely solitary, generally irregularly matted to form free- 

 floating flocculent masses. Plant masses blood-red to dirty purple, be- 

 coming lilac when dried. Trichomes straight, elongate, not constricted 

 at cross walls of cells, and slightly tapered at apex with the terminal 

 cell of mature trichomes obtuse-capitate. Cells cylindrical, slightly 

 longer than they are broad. Cell contents with numerous reddish 

 pseudovacuoles, sometimes with rows of granules at the cross walls. 

 (Euplanktont). 



Cells 2.2-5 /x, broad, 4^6 /*. long. 



Geneva (aa), Pine (1) (aa). 



This species is closely related to 0. riibescens D. C., but if Gomont 's 

 monograph of the Oscillatoriaceae must be taken as the starting point 

 for nomenclature of the group the two are distinct. Both species are 

 peculiar in that they produce blooms in lakes at a time when the water 

 is very cold or covered with ice. The masses of filaments do not have 

 the usual yellowish-green color but are blood red to dirty purple and 

 the phenomenon is spoken of in Europe as "bloody" or "Burgundy" 

 bloom. 



Olive has described the occurrence of such a bloom in Pine lake of 

 this state and discussed the literature of the subject. The alga also 

 appeared in profusion in Lake Geneva this (1918) spring at the time 

 when the ice was beginning to disappear. It was not frozen in the ice 

 but grew luxuriantly in the water below the ice and gave a deep red- 

 dish color that was especially noticeable in the cracks between the ice. 

 The alga had not been noted in the lake before this time and its sporadic 

 appearance is quite like the sporadic appearance of 0. riibescens in the 

 Swiss lakes. The excessive growth of 0. prolifica is not wholly corre- 

 lated with cold water since it has remained present throughout the 

 summer, but not in such quantities as early in the spring. This abund- 

 ant growth of the alga in the summer has also been noted in a Massa- 

 chusetts lake by Hyams and Richards and furnishes a physiological as 

 well as a morphological distinction between 0. prolifica and 0. riibes- 



