358 



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 XXVII. 



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. PI. X. and XXVII.). 



The flood which wipes out the rising June pulse in the river 

 ( PI. 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 (PI. 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. PI. 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 



