472 



PLANKTON PRODUCTION AND TEMPERATURE. 



in Thompson's Lake, 29 per cent. The difference would be in- 

 creased if the aberrant data of the late autumn of 1897 were 

 removed from the records. Low temperatures thus tend to 

 depress production in ])oth channel and backwaters, and high 

 temperatures to increase it. 



The minimum production of the year occurs in the river, 

 and with few exceptions in the backwaters, in January-Febru- 

 ary, the two months of minimum temperature. With the 

 period of rising temperatures in March -May there comes gen- 

 erally at all of the stations a rapid rise in plankton production, 

 culminating in the vernal pulse in the last days of April or the 

 first of May at about 60°-70°. The effect of this is seen in the 

 generally high average production in April and May in both 

 channel and backwaters. With the establishment of the sum- 

 mer period of maximum temperatures, which includes the 

 months of June-September with the exception of a few days 



