396 
age in the unstable bottom, and refuge was had under the lee 
shore, but still in usual depths and open water. In several in- 
stances in overflow stages, when the ice was too heavy to break 
and too light to carry our load, it was necessary to make the 
collection near the margin of the lake in effluent waters. These 
variations in the location of the point of collection introduce 
no error of consequence into the series, judging by the results 
of an examination of the local distribution of the plankton in 
this lake, the details of which cannot be given in the present 
paper. 
With the exception of the single pump collection on Feb- 
ruary 28, 1896, all collections prior to May 20 of that year were 
made by the oblique-haul method, and thereafter by the plank- 
ton pump. 
This lake is a type of the larger reservoir backwaters, such 
as Meredosia Lake, Clear Lake, and others found in the bottom- 
lands of the Illinois and maintaining a constant connection 
with that stream. An examination of its plankton content 
will therefore serve to throw light on the relation which lakes 
of this type bear to plankton production in channel waters. 
PLANKTON PRODUCTION. 
1894. 
(Table VIII., Pl. XXXV.) 
There are but 5 collections in this year, from June to De- 
cember, at an interval of a month or more, with an average 
production of 8.89 cm.’ per m.* and a maximum of 24.92 on 
June 7. 
An inspection of the hydrograph (Pl. XX XV.) of this year 
reveals the fact that only the first two collections were taken 
under conditions which permitted any run-off from the lake to 
the river, and both of them at times—that is, in falling levels 
below 6 ft.—when the run-off was largely, if not wholly, through 
the tortuous slough at the up-stream end of the lake. The pro- 
duction in the lake (24.92 and 10.74) at these times was 33- to 
