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 $7 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 factorsinvolved. 
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- 
