309 
instance but two, Oct. 14 and 29. In the first of these, silt-laden 
flood waters in the river, but not in the lake, interrupt the par- 
allelism. Inthe second instance the production of the lake de- 
clines and that of the river rises—again as a result of the prior 
flood conditions, as will appear on a comparison of the sequel 
of the June and August floods in the two bodies of water. In 
these, as also in the October flood, there are indications that the 
rising plankton pulse common to both is temporarily suppressed 
in the river and continues undisturbed and reaches an earlier 
culmination in the lake, but only a delayed one of slight ampli- 
tude in the stream. 
The average production in the lake in the last four months 
of the year exceeds that in the river by 52 per cent. and in five 
of the seven collections. 
The comparison of production in Quiver Lake and the Ilh- 
nois River in 1896 is very instructive in several important par- 
ticulars. In the first place, both the relative and absolute pro- 
ductivity of the lake has increased, rising from 1.08 and .78 
em.’ in 1894 and 1895 to 2.59, an increase of two- to three-fold. 
The ratio of productivity in the lake to that in the river in 1894 
was | to 2.3; in 1895, 1 to 4.1; while in 1896 it falls to 1 to .45. The 
low average in the river is, as has been shown, the result of the 
repeated flushing by storm waters. The increase in the lake is 
due to the higher levels and increased impounding function, 
and to the actual and relative decrease in its vegetation. The 
combined result of the operation of these factors is that in this 
year the lake waters cease to be diluents of the channel plank- 
ton and become sources of enrichment. Considering the areas 
of their respective drainage basins, and basing calculations on 
the yearly averages, the net result of the contributions of Quiy- 
er Lake is a rise in the plankton content of channel waters 
from 1.16 em.’ per.m.* to 1.18—an increase of a little less than 
2 per cent. 
Not only was the average production in the lake (2.59) 
greater than that in the stream (1.16), but individual collec- 
tions upon coincident or approximate dates exhibit the same 
