samples, but were lacking in autumn. Cosmarium was found in all but 

 one of the periods, and in late October there were h thousand units. 

 Pediastrum was consistently present, but always in small numbers. 

 Kirchnerella, Errerella, Closterium, Ankistrodesmus, and Westella 

 were very rare and were restricted to the summer months. 



Four genera of blue-green algae were important constituents 

 of the plankton: Coelosphaerium, Oscillatoria, Merismopedia, and 

 Gomphosphaeria. All were rare prior to the middle of August. 

 Coelosphaerium was first present in considerable numbers in early 

 August, and was abimdant in late August and early September (29 and 28 

 thousand units). It was not noted in late September, and was rare in 

 October. Oscillatoria was present in every period except late August, 

 but was abundant only in the last three periods, showing a maximum of 

 26 thousand units in late October. Merismopedia was the most con- 

 spicuous of the blue-greens. It first became abuiidant in early August 

 and increased gradually to a maximum of 129 thousand units in late 

 September. Gomphosphaeria was absent until mid-summer and rare during 

 the remainder of the surmer. It increased rapidly in early September 

 and reached a maximum of U8 thousand units in late September. In 

 October it was about one half as abundant as at the pesik. Microcystis 

 was present in only six periods, and the maximum count was li thousand. 

 Anabaena was noted in only four periods, and was always rare. 

 Aphanizomenon was found in five periods, with a maximum count of 

 5 thousand at the end of the season. Lyngbya was present only in 

 October and then in small numbers. 



Genera belonging to groups other than the diatoms, greens, or 

 blue-greens, such as Dinobryon, Geratium, Peridinium, and Euglena were 

 noted from time to time but were never conspicuous in the plankton. 



It should be noted that the foregoing account refers only to 

 the open waters of the lake and not to the shallow, protected areas 

 along shore and about the islands. Such genera as Volvox, Eudorina, 

 Gonium, Anabaena, Microcystis, Aphanizomenon, Euglena, and Geratium may 

 each be explosively abundant for a few days in the protected areas, and 

 thereafter occur only sparingly or not at all. Apparently these "blooms" 

 are localized and have little effect on the plankton of the open waters. 



Season of 1930 



Seasonal distribution of phytoplankton groups. The sampling 

 season of 1930 was begun in early April and discontinued in early 

 October. Seasonal changes in abundance for this period are shown in 



155 



