247 
this species prevails lies in the southern third of the lake and 
along its sides for a distance of several hundred feet from 
shore, and again at the northern end for a distance of three 
quarters of a mile from the outlet. During low-water years 
scattered clumps of Ceratophyllum and Potamogeton were found 
as far north as the middle of the lake. Thus, at all seasons 
about half of the lake—often two thirds of it—is open water 
with scarcely a trace of fixed vegetation. 
The seasonal changes in the vegetation of this lake are very 
marked. In midwinter, during the ice blockade, which contin- 
ues much longer upon the lakes than upon the river, the vege- 
tation is not much in evidence. At low stages dead rushes 
rise above the ice in a few places, but give little hint of the 
great mass of broken and more or less comminuted vegetable 
debris which covers the bottom in those portions with vegeta- 
tion of a semi-littoral character. This debris is of great extent, 
and in the absence of current and buoyancy is not carriedaway, 
but remains to enrich the waters and the unstable ooze upon 
which it lies. Most of the vegetation in this belt is dormant at 
this period, little trace of green appearing on the half-buried 
root-stalks and rhizomes of the perennial species belonging to 
this zone. In the deeper water, on the other hand, a consider- 
able quantity of Ceratophyllum, with some Elodea, remains upon 
the bottom throughout the winter, keeping its foliage beneath 
theice. This isan important factor in preserving the equilib- 
rium in the gaseous contents of the water, and thus in the main- 
tenance of the winter plankton. 
With the rise in temperature in spring the vegetation starts 
into growth which the spring floods to a large degree conceal. 
This growth and the decline in river levels combine to make 
its appearance at the surface or its emergence above it some- 
what sudden. The greatest growth takes place during the 
months of May and June, and is in large part attained by the 
close of the latter month. The changes subsequent to this pe- 
riod which are incident to growth are but slight, and have but 
little effect upon the “waterscape.” 
