398 
temperatures in the shoaler and clearer impounded waters 
which are drained off through Quiver Lake. The temperatures 
of surface waters in the lake from February up to the time of 
the maximum are from 1° to 15° higher than in the river, as 
will be seen on comparison of the thermographs on Plates X. 
and XX VII. 
The May pulse in Quiver Lake attains 8.14 cm.’,—more than 
twice the amplitude of that in the river, 3.56,—while the aver- 
age production for the month in the lake (2.99) exhibits a sim- 
ilar ratio to that of the river (1.30). The very sudden decline 
from 8.14 on the 8th to .51 on the 16th attends a decline of 
about 2 ft. in river levels at a stage which cuts off the lake from 
large impounding areas to the north, and also, at this season of 
the year, brings the submerged flora to the surface. These two 
factors combine in effecting this sudden drop in production in 
the lake before it appears in the stream (cf. Pl. X. and XXVIL.). 
The flood which wipes out the rising June pulse in the river 
(Pl. X.) increases the impounding area and relative occupation 
of the lake water by vegetation and permits a pulse of some 
amplitude (2.60) to develop in the lake, while only a belated 
and slight development appears in the contiguous river. As 
levels fall in July and impounding areas are again cut off and 
vegetation anew occupies a relatively larger proportion of the 
lake, production declines to so slight an amplitude that a July 
pulse can hardly be traced (Pl. XXVII.), and the average 
monthly production in the lake falls to a fifth of that in the 
stream, whose plankton content it had in previous months of 
the year exceeded. 
With the rise of the August flood, production again assumes 
a pulse-like character, lagging throughout its development a 
few days behind that in the adjacent stream (cf. Pl. X. and 
XXVII.), and lacking in the lake the cleft in the apex of the 
curve caused in the river production by the flushing action of 
local floods. 
The seven collections during the remainder of the year ex- 
hibit a similar direction of movement in production in every 
