399 
stances (cf. Pl. IX. and XX XVI.);in the case of Quiver Lake the 
agreements number 7 out of a possible 12 (ef. Pl. XX VI. and 
XXXVI.); in the production in Dogtish Lake the correspondence 
is found in 9 out of a possible 12 (ef. Pl. XXX. and XXXVI.); 
while in Flag Lake there are 2 out of 3 (ef. Pl. XXXIIT. and 
XXXVI.). 
The agreement is lessened in this year, it seems, by the hy- 
drographie conditions. The low water affords less opportunity 
for a mingling of the waters of the stream and its backwaters, 
and also serves to bring out the local environments at each of 
the stations. Thus Thompson’s Lake has but little connection 
with other backwaters at any time during the year, and ingress 
oregress of channel waters was but very slight during six months 
of the twelve in this year. Vegetation also gained more ex- 
tended possession of this lake in this year than in other seasons 
of our operations. Low water also tends to make the channel 
plankton more directly affected by its peculiar factors, such as 
sewage. It is noticeable that the agreement in production is 
most marked between Thompson’s and Dogfish lakes, both back- 
waters of somewhat similar character in respect to tributary 
waters, relation to the channel, and vegetation. 
The most marked differences between production in this 
lake and the channel appear in the respective amplitudes of 
the pulses of production in April-May and June-July. In the 
lake the-rising vernal pulse attains the exceptional volume of 
28.2 on April 10 to.52in the river on the 9th, a difference which 
may in part be due to the earlier warming up of the shoal- 
er lake waters. The maximum (61.44) in the lake is 12- fold 
that observed in the stream. The June-July production in the 
river, on the other hand, is 3- to 5- fold that in the lake, the 
contrast being due on the one hand, it seems, to the temporary 
exhaustion either of the chemical substances utilized by the 
plankton or of the reproductive capacities of the planktonts of 
the lake waters, and, on the other, to the increased sewage con- 
tamination in the stream as a result of low levels. The direc- 
tion of the changes in production, however, remains the same in 
