THE LIFE OF DEVIDS LAKE 49 



bottom similar to those of Main Lake. The shallowness of the 

 lake renders it more quickly responsive to the air temperature than 

 the deeper waters of the other lakes. In the earlier years of the 

 work (1911-14) there were the same differences, altho not so mark- 

 ed, between the shore and mid lake temperatures as noted for 

 Devils Lake, but at present such differences are undoubtedly negli- 

 gible, if existent. Its shallowness renders the temperature of the 

 entire body higher in summer, while its greater salt content renders 

 the freezing point, and hence the water temperature, somewhat 

 lower in winter than the others. At present it freezes solid in win- 

 ter. 



The chemical character of East Lake is naturally similar to 

 that of the main body, but has gradually become more concentrated 

 with decreasing depth (table 3). Formerly East Lake showed the 

 same zonation as Main Lake, but at present no such distinction can 

 be made. Plancton records cover the period from 9/2/13 to 9/1/14, 

 with a few prior thereto. They were taken at the shore and at 

 depths of 0.6 and 2.0 m. The plancton species, at the time these 

 records were made were similar to those of i\Iain Lake. 



Probably owing to poor preservation of material the data for 

 Micrococcus, Sarcina, Merisniopedia and Dictyosphaerium are inade- 

 quate and have accordingly been omitted. Brachionus plicatilis 

 which appears in the collections of June 21 and July 12 only, is 

 also omitted. 



MISSION LAKE (pl. 8). 



This is a small body of water resulting from the isolation of a 

 bay of the main lake in 1909 or 1910. In spite of the fact that the 

 lake probably receives a small amount of seepage from a fresh 

 water lake situated on a terrace about a half kilometer distant, its 

 history has been similar to that of East Lake, so that today it is 

 only a shallow pool, nearly filled with foul smelling ooze. In win- 

 ter it freezes solid and in summer is heated to 30° so that its life is 

 subjected to a strenuous existence. 



The chemical analysis and osmotic pressure are given in table 3. 

 The life of Mission Lake in kind, distribution and abundance was 

 formerly the same as that of the parent body, but with its separa- 

 tion, and consequent changes in its physico-chemical character, great 

 changes have naturally also taken place in its fauna and flora. 

 Only a few quantitative collections have been made, so that there 

 are no records available of the seasonal distribution. Compared with 

 collections from Main Lake these collections show a considerably 

 greater number of zooplanctonts and much fewer phytoplanctonts 

 than collections taken at the same, or nearly the same time from the 

 former water. Whether this difference is constant or not the 

 collections are too few to determine, and if constant, the reason is 



