316 
the remainder of the year. All of the collections were made 
with the plankton pump. This was a year of high winter floods, 
a normal March rise, a belated June rise, but prolonged low 
water throughout late summer and autumn. The collections 
afford a good opportunity to observe the result of prolonged 
low water and a late autumn. 
From February to July the collections are too infrequent 
to enable us to trace the curve of plankton production or de- 
tect any cyclic movement. Of the two collections in February 
the first was made under the ice sheet and yielded little plank- 
ton or silt. The second, made while the ice was going out, 
contained much more silt—the result of the rising flood. Both 
were very poor in plankton (.03 and .05 respectively), but 
neither showed the least evidence of stagnation conditions such 
as obtained in 1895. This was due to the larger volume of wa- 
ter and the swifter current and greater dilution of sewage, as 
well as to the briefer ice blockade and the direct connection of 
channel waters with the vegetation-rich bottom-land lakes and 
forests when the ice was full ofair-holes, so that the equilibrium 
of gases inthe water did not undergo so violent a disturbance 
as in 1895, 
In the March collection there is evidence of the increas- 
ing production as vernal temperatures approach. The col- 
lections of April and May were both made on the decline of 
the March flood, and both lie at temperatures between 60° 
and 70°. This spring presented ideal conditions for a very 
large plankton production, namely, uninterrupted decline, with 
run-off of impounded backwaters in which the plankton had 
had abundant time to breed. Neither of our vernal collections 
shows any large production, though that of April lies in the 
period in which the vernal maximum may be expected. It is 
not improbable that a maximum occurred but was not detected. 
The June collection lies in the midst of turbulent flood waters, 
as the great proportion of silt (26.33 cm.* per m.*) indicates. 
From this point until the close of our operations in March, 
1899, the weekly interval of collection was adopted, and the 
