434 
vember the production is 10- to 8- fold the average, and in De- 
cember 9 per cent. above the mean for that month. 
In Thompson’s Lake the mean of the monthly averages, 
13.31 em.’ per m,' is 61 per cent. in excess of the mean of all 
the months of our records, though but-3 of the 9 months repre- 
sented in the records of 1895 are above the average. ‘The first 
two of these, April and May, owe their predominance to a ver- 
nal pulse of unusual volume, andthe small number of collections 
gives these months abnormally high averages, while the large 
production in July may be attributed to the enrichment of the 
lake in this year by an invasion of plankton-rich river water 
from the channel (Pl. XXXVI.). The deficiency shown in the 
records of the remaining 6 months, falling from 10 to 70 per 
cent. below the averages of our records for these months, finds 
its possible explanation in the relatively greater dominance of 
vegetation in the lake in this season, due to two successive 
years of low water and the prevailing low levels. Collections 
in this year were, moreover, taken near the margin of the veg- 
etation belt of the lake. 
Production in this, the second, year of low water, and the 
lowest in our term of operations in all the backwater plankton 
stations but Quiver Lake, is above the average in the year as a 
whole, though falling below it in 57 per cent. of the time rep- 
resented, 
The apparent suppression of the vernal pulse in the river 
and in Quiver and Dogfish lakes may be attributed to the ab- 
sence of spring overflow and the consequent elimination of vast 
impounding and breeding areas normally present at this season, 
and also to the direct delivery of tributary water to the chan- 
nel and increased relative diluent action of the slight April rise 
(Pl. IX.) in both the river and Quiver Lake. The low levels 
also serve to bring the vegetation of the two lakes named into 
early dominance, and the relative occupancy is also increased 
by the second year of low water and no removal of the accumu- 
lated growth by flood action. Thompson’s Lake, on the other 
hand, owing to its great extent of open water, is less affected 
