368 
ern side can a substratum of harder sandy clay be reached be- 
neath two or more feet of this deposit. With the exception of 
a narrow fringe along the eastern side, the vegetation lacks the 
lilies, rushes, sedges, and other emergent plants which charac- 
terize the eastern shore and northern end of Quiver Lake proper 
(Pl. XVII.). It consists (Pl. XVIII.) almost exclusively of Cer- 
atophyllum, Elodea, and Potamogetons, which, in the low water 
of 1895, represented in the plate, filled the lake from center to 
periphery. Irregular openings in this dense growth appear oc- 
casionally in the area, and are modified by the shifting of the 
lightly attached vegetation, by wind, and by flood water. 
Except at high water and during the rapid run-off of im- 
pounded backwaters no appreciable current traverses this area. 
It receives no immediate contributions of spring or creek water 
along its margins, but depends entirely upon backwater from 
Quiver Lake or flood invasions for its supply. 
The examination of the plankton content of its waters ac- 
cordingly affords an opportunity to test the effect of this im- 
pounding factor, and also serves to throw some further light on 
the effect of vegetation on plankton development in impounded 
waters. 
COLLECTIONS. 
The collections in this lake cover a period of two years— 
from April 29, 1895, to June 28, 1897 (Table VI.). They num- 
ber 48, and are distributed in much the same manner as those 
in Quiver Lake in the same period. The collections of 1895 and 
those of 1896 through May 8 were all made by the oblique-haul 
method with the single exception of that in the flood of Feb. 
27, which was one of repeated vertical hauls. The collection 
of May 19, 1896, was made in the midst of rapidly growing veg- 
etation by dipping from surface waters, which then afforded no 
area suitable for an oblique haul. The oblique hauls were made 
for the most part near the center of the lake in a channel freed 
from vegetation a day prior to the collection. From May 21, 
1897, all collections were made by the plankton pump in open 
stretches of water amid the vegetation. 
