477 



The effect of the autumnal decline, and, in general, of low- 

 ered temperatures, in depressing production is apparent in not 

 a few instances in our records. It can be seen in the October- 

 November thermographs and curves of plankton production 

 of channel waters in 1894-1898, and in those of Quiver Lake for 

 the same years ; is much less apparent in Thompson's Lake, 

 especially in 1897, even when temperatures have fallen ; and 

 is often but feebly developed in Dogfish and Flag lakes in 

 1895-1897, while in Phelps Lake in 1896 and 1898 there are 

 pulses of considerable magnitude (51.6, and 99.86) in this period 

 of decline of temperature. The minima demarking these 

 pulses are, however, of less than the usual amplitude. This 

 depressing effect is thus traceable in all localities, but is bet- 

 ter developed in stream than in lake waters, appearing most 

 clearly in the channel and Quiver Lake, where, at this season of 

 the year, tributary waters are present in considerable propor- 

 tion. 



Our water temperatures and the records of the United 

 States Weather Bureau at Havana and elsewhere in our lo- 

 cality reveal many instances of heat pulses at various seasons 

 of the year. There is little regularity in their duration or 

 amplitude. When plotted from the means of the tri-daily 

 readings of the air temperatures at Havana they do not ex- 

 hibit delimitations as well defined as those, for example, of a 

 fully observed plankton pulse. Their amplitude, except in 

 winter months, rarely exceeds 20° between extremes, and their 

 duration is usually less than a fortnight between minima. That 

 these fluctuations affect the course of plankton production can- 

 not be doubted. A detailed comparison of the course of produc- 

 tion in 1896 and the thermograph of that year will show that, 

 predominantly , rises of temperature attend or precede rising pro- 

 duction, while declines in heat are often correlated with de- 

 creased production. This may be largely coincidence, or, in 

 some cases, the common effect of cooler, barren flood-waters, 

 especially in the case of the records of channel production. A 

 close comparison, however, of the planktograph in Phelps 



