70 THE LIFE OF DEVILS LAKE 



irregularity of their distribution, and their frequently greater 

 abundance in the shore collections, to which attention has already 

 been called, the charts show little except that, like other algae, they 

 are much more abundant in summer than in winter. That this 

 is due to temperature is unlikety, because in some instances at least 

 there is a marked increase in early spring or late autumn. Similar 



Figure 21. Seasonal distribution of diatoms in individuals in East Lake. 



conditions are described by Needham and Lloyd (1916, pp. 302-3) 

 and Marsh (1900, p. 176). In r. letter to the writer from Grand 

 Island, Nebraska, (Dec. 31, 1920) Professor Elmore says, "Here, 

 diatoms are much more abundant in the winter, when the water 

 is partly frozen over." Their infrequent occurrence then in the 

 winter collections from Devils Lake is probably due to other factors, 

 such as reduction in amount of light or dissolved food-stuffs. 



In shore collections, especially in bays of the lake, the numbers 

 of diatoms, especially Navicula and Synedra, may run very high, 

 the maximum number recorded being found at the head of Creel 

 Bay, near the mouth of the sewer ditch from Devils Lake City, on 

 August 13, 1912, as follows: total 1292, Navicula 748, Synedra 376, 

 Cymbella 128, scattering 40, per cc. Other high records are from 

 the same place: total 292, Navicula 144, Synedra 140, scattering 8, 

 date?, and total 168, Navicula 152, Synedra 16; Aug. 9, 1916, and 

 from the mouth of Minnewaukan Bay on July 13, 1916, Navicula 

 116, Synedra 4. These are the only records of more than 100 

 diatoms per cc, but there are a few others of 90 or more. 



Other species of occasional occurrence in the plancton are 

 d o n t i d i u m elongatum, Mastigloia elliptica and Carapylodiscus 



