473 



of rising and falling temperatures at the beginning and close 

 of the season, there comes, as a rule, a decline in production 

 from that of the vernal season. In channel waters this amounts 

 to 16 per cent, of vernal production, or, omitting the single 

 aberrant datum of June 1895, to 44 per cent. In the backwa- 

 ters, owing to the combination with various local factors, such 

 as tributary waters and vegetation, the change from vernal pro- 

 duction in midsummer varies greatly in different localities. 

 Thus, in Quiver Lake, where vegetation and the proportion of 

 tributary waters is increased in summer, the decline in that 

 season amounts to 87 per cent., while in Dogfish Lake, where veg- 

 etation alone is the main disturbing factor, the decline is 74 per 

 cent, of the vernal production, as seen in the April-May aver- 

 ages. In Flag Lake, where also vegetation enters as a disturb- 

 ing factor, the decline is 80 per cent. In Thompson's Lake, where 

 disturbing local factors are less in evidence, it is but 69 per cent. 

 In Phelps Lake, in contrast with all the other localities, pro- 

 duction during the period of maximum heat exceeds that in the 

 vernal season by 68 per cent. Thus the period of maximum 

 heat in most localities attends a depression in production, but 

 the exception in Phelps Lake is so striking as to preclude any 

 conclusion that summer heat is necessarily inimical to large 

 production, or that it is of necessity the most potent of the co- 

 operating factors. The omission of the averages for August 

 and September in 1898 from the Phelps Lake data would make 

 the average production in the period of maximum heat 33 per 

 cent, below that of the vernal months, and bring this locality 

 into agreement with the other stations as to the depressing 

 effect of summer heat in plankton production. It should be 

 emphasized in this connection that these conclusions apply to 

 catches of the silk net only, that the summer temperatures of 

 our waters approximate 80° on the average and frequently rise 

 above it, and that temperature is only one of the factors involved. 

 Following the period of maximum summer heat is that of 

 decline in October-November — including also a part of Sep- 

 tember, or even December in some seasons — to the winter min- 



