219 



plankton pulses of 1897 (PI. XLVI.) in the warm months of 

 May and September, but the increases noted with the pulses of 

 plankton in the winter in the Illinois River are not apparent 

 in the case of the pulses of February and December in this 

 stream, though no decrease appears as in the summer months. 



In Quiver Lake in 1898-99 (PI. XLVIII.) a seasonal move- 

 ment in the albuminoid ammonia and the organic nitrogen is 

 evident, though it seems to accompany the access of sewage- 

 contaminated waters of overflow, as appears on comparison 

 with the chlorine curve. This seasonal movement is evident 

 as a depression of the curves during the warm and low-water 

 months, and as an elevation during the colder months of the 

 flood period. As in Illinois and Spoon rivers, the plankton 

 pulses in Quiver Lake of the warm period, in May and June, are 

 attended by a temporary decrease in these nitrogenous sub- 

 stances. A still more marked decrease in both albuminoid 

 ammonia and organic nitrogen attends the winter pulse of 

 plankton in February, 1899, while that of the preceding De- 

 cember appears with an upward movement of the organic 

 nitrogen and a downward one in the albuminoid ammonia. 

 The correlation between the movement of albuminoid am- 

 monia and organic nitrogen and of the plankton is thus in this 

 instance (predominantly, at least) similar to that noted else- 

 where in the warmer months. The very slight ripples in the 

 plankton curve in July, August, and September attend minor 

 increases in these nitrogenous substances, a feature noted else- 

 where in colder months. 



In Thompson's Lake (PI. L.) the albuminoid ammonia, the 

 organic nitrogen, and the plankton are all more abundant and ex- 

 hibit greater fluctuations than they do in Quiver Lake. These 

 conform in a general way to the tendencies noted in other 

 localities. The amounts present during the colder months, 

 October to May, are a trifle greater than in the intervening 

 warmer period. There is also a temporary decrease in those 

 nitrogenous matters attending plankton pulses in the warm 

 months. This appears with the pulses of June, July, and 



