476 



So also in 1897, the means of our records of water tempera- 

 tures for September, October, and November of that year are 

 2.9°, 7.6°, and 2.7° above the average of the monthly means for 

 all years. This maintenance of high temperatures into the pe- 

 riod of normal autumnal decline is apparently one of the fac- 

 tors tending to make production in these months of this year 

 greatly exceed that of the same season in other years. In chan- 

 nel waters in these months of 1897 (see table following p. 342) 

 production is from 13 to 250 per cent, above the mean of all 

 years, and often 10- to 20-fold that in other years. In Thompson's 

 Lake the excess in 1897 is even greater, ranging from 87 to 233 

 per cent, of the mean of all years, and from 1.6 to 28 times that 

 in the same months in other years. The higher temperatures 

 do not suffice, however, in the case of Quiver Lake, to overcome 

 the other factors tending to depress production there in these 

 months, and we must conclude that, although all-pervading 

 and potent, temperature is nevertheless not always pre-emi- 

 nent among the environing factors of the plankton. 



We thus find that in a general way, in conjunction with 

 other factors, rising temperatures tend to increase, and falling 

 to decrease, plankton production, and that in the same locality 

 the warmer months generally yield more plankton than the 

 colder ones. On the other hand, minimum temperatures when 

 once established are not of themselves inimical to a considera- 

 ble plankton production. Evidence of this is to be found in 

 the not infrequently increased production in December over 

 that of several months preceding. This is perhaps most notice- 

 able in the records of 1898. Thus in channel waters the am- 

 plitude of the December pulse (PI. XII.) exceeds that of all 

 other months since the last of June, and the December maxi- 

 mum in Phelps Lake (43.14) exceeds in amplitude all other pro- 

 duction in our records for 1898 in all other localities save only the 

 single apex of the vernal pulse (51.39) in Thompson's Lake. It 

 is, however, only about one fifth of the August maximum 

 (224.48, PI. XLII.) in Phelps Lakeitself, so that the depressing 

 effect of lower temperatures is still apparent if we limit com- 

 parisons to a single locality. 



