344 
Lake, where tributary creek and spring waters form a larger 
proportion of the content of the lake, and 19 of the 30 are in 
the low-water period, July-November, when the proportion of 
tributary waters is greatest and the impounding function at its 
lowest level, and vegetation at its height. Of the remaining 
18 instances of deficiency, 6 are in Dogfish Lake, which is to 
some extent under the influence of the hydrographic condi- 
tions of Quiver Lake, and is likewise dominated by vegetation. 
Three of the 6 cases of deficiency appear in July-August, in 
the height of the dominance of vegetation and at times of 
slight run-off. Two instances at the same season and under 
similar conditions of vegetation and discharge appear in the 
monthly averages of Flag Lake. In the monthly averages of 
Thompson’s Lake there are 8 instances of deficiency, but in half 
of these the deficiency is less than 30 per cent. There are but 
2 cases of deficiency in Phelps Lake, both at times when Spoon 
River tributary water was passing through the lake. Further- 
more, 33 of the total 48 instances of deficiency in production 
in backwaters, as compared with channel, occur in July—De- 
cember, during the low-water period of least run-off of im- 
pounded backwaters, and of the remaining 15 instances during 
the January-June period some probably result from insufficient 
data, and others are found when the stagnation (Moina) pulse 
of June, 1895, occurred in the river. 
We must, therefore, conclude that the greater part of the 
backwaters predominantly bring to the channel in their run-off 
a richer plankton than that with which their contributions are 
mingled. The extent’ of this predominance and its changes 
with the seasons and from year to year will be seen in the 
table of monthly means following page 342. It is summarized 
in the following table, which gives the mean plankton content 
in channel waters for each month and the average of the 
monthly means of the five backwaters, Quiver, Dogfish, Flag, 
Thompson’s and Phelps lakes, together with the ratios between 
channel and backwater production in each month. 
An inspection of this table shows that during the colder 
