370 
the contiguous but impounded and current-free waters of Dog~ 
fish Lake contain 229 times as much plankton. 
The increased production following the September flood is 
apparent in all three localities, but reaches its highest level 
(4.65) in Dogfish Lake, the region where the impounding factor 
is greatest, while the least increase and quickest decline is in 
Quiver Lake, where tributary waters of recent origin are in 
greatest proportion. The low production in October is com- 
mon to the three localities, reaching a slightly lower level in 
the lakes (.13 and .52) than in the river (.57). The consider- 
able increase in production in November-December attains the 
highest level in Dogfish Lake (5.01 and 10.57), exceeding by 100- 
and 17-fold that in Quiver Lake (.05 and .63), and that in the 
river (4.37 and 2.60) by 1.2- and 4-fold. Here also the effect of 
the quieter impounding waters of Dogfish Lake is apparent in 
this relatively greaterdevelopment. The large plankton content 
on Dee. 19 (10.57) seems to be due to a combination of several 
favoring environmental factors. This collection was made 
after a steady but slight rise lasting for over five weeks, fol- 
lowed by ten days of gentle decline in levels and contracting 
margins of the lake. The steady rise to levels which intro- 
duced no run-off currents through the lake established the im- 
pounding function to its fullest, and invaded a considerable 
stretch of margins rich in dead and decaying vegetation. There 
is also at this season of the year less growth and more decay of 
the Hlodea and Ceratophyllum which abound in the lake. The 
collection was taken when the December flood had just be- 
gun to rise (about 2.6 feet) and with the combined action 
of wind and waves which attended the storm then raging had 
torn loose the vegetation and dislodged many of the smaller 
Crustacea and insect larve which find shelter in it. There 
were at the time 572 Allorchestes per m.* adventitious in the 
plankton. A part of this large production is thus adventitious 
owing to disturbed hydrographic conditions. Nevertheless, 
there still remains after such contributions are deducted a con- 
siderable plankton of normal constitution (mainly Cladocera), 
