104 THE LIFE OF DEVILS LAKE 



able physical environment, the shallowness, and the lack of inlet 

 or outlet to the lake. Shallow lakes, in general, are better plancton 

 producers than deeper ones, and Devils Lake is no exception to 

 the rule. It is well known, also, that certain temporary pools, may, 

 at times, be swarming with life, while in bodies of changing water, 

 especially rivers, the number of organisms is frequently much less. 



A comparison of the amount of plancton in lakes and rivers is 

 difficult to make because of the great individual differences between 

 different bodies of water, due to various factors. Thus Birge & 

 Juday (1922) in their study of three Wisconsin lakes* found that 

 the total amounts of dry net plancton in milligrams per cm. ranged 

 from 491 for Mendota to 2182 for Waubesa, while the corresponding 

 amounts for centrifuged material ranged from 3090 to 5665. Apstein 

 (1896 p. 92) found variations running from 4.5 cc. pr. cm. to 454.3 

 cc. and similar variations have been found by other authors. 



A comparison between the amount of plancton in lakes and rivers 

 made by Whipple (1914, p. 20), iu spite of great individual varia- 

 tion, shows clearly enough the relative paucity, of plancton in many 

 streams as compared with lakes. 



Kofoid (1908), however, records amounts of plancton for the 

 Illinois River,* which compare favorably with the figures for most 

 lakes. So much depends on the individual character of the water in 

 question that it is unsafe to generalize too broadly. 



A comparison between the plancton production of Devils Lake 

 and that of other waters is difficult to make because different 

 workers have used different methods of expressing their results, and 

 in many cases, moreover, the period of observation is too brief to 

 enable one to draw any conclusions concerning maximum, minimum 

 or average productivity of the water in question. Some data art, 

 however, available and maj^ be of interest. The average number of 

 Crustacea (incl. nauplii) in Devils Lake for the periods of collection 

 from 1911 to 1923 inclusive is 228,000 pr. cm. From table B in 

 Birge (1897) I have computed the average for Lake Mendota in 

 1895-96 as 37,350 pr. cm. In each case the average was obtained 

 "by adding all the collections for a given date and dividing by their 

 number. From the data given by Birge & Juday (1914, '21) I have 

 computed the averages for Canandaigua, Cayuga, Hemlock, Otisco 

 and Seneca Lakes, N. Y. and Green Lake, Wis., the maximum of 

 which is 67,800 pr. em. in Otisco Lake on August 16, 1910. It 

 should be borne in mind that these averages are for very few col- 

 lections; for Hemlock, Green and Otisco Lakes, only one; and for 

 the others three each. 



The rotifer average for Devils Lake for the same period is 

 350,000 pr. cm., while, for the reproductive season only, the average 



•Mendota, Monona, Waubesa. 

 ♦See Kofoid, p. II, p. 16. 



