177 
In 1897-98 the lakes closed the last days of November 
and opened again on December 12, freezing again December 
17, and not clearing entirely until February 14. Rising water 
continued from January 10, so that stagnation conditions did 
not ensue. The river also closed partially early in December, 
opening and closing again with the lakes. The first ice went 
out with the rise on January 11. The river closed again Jan- 
uary 27, and the ice went out February 9 and 10. Again on 
February 21 ice was present, and for several days following. 
In 1898-99 ice again formed early in December and par- 
tially closed the river during the month, going out about the 
27th and reappearing on the 30th. This went out gradually 
January 17-24, and the river froze over again on the 26th and 
remained closed fora month. Thin ice formed March 5, re- 
maining only three days. The lakes closed early in December, 
the ice never entirely disappearing until the middle of March. 
Partial breaking up occurred at the times of breaking up of the 
river ice. These partial openings and the changes in level 
were sufficient to prevent a period of stagnation. 
OTHER METEOROLOGICAL FACTORS. 
As indicated in Tables III.-IX., at each plankton collection 
observations of the direction and force of the wind, with its 
effect upon surface conditions and on the state of the sky, were 
recorded. The relation of these factors to the plankton may 
not seem intimate or apparent. They have more bearing on 
the subject of vertical movements of the plankton, data upon 
which will be found in the study of the surface and bottom col- 
lections made with each of the vertical collections which form 
the basis of the present paper. The surface waters affected by 
the intensity of the sunlight and the movements caused by the 
wind form relatively so large a part of the environment of the 
river plankton that these factors are much more widely opera- 
tive here than in the lakes, where the surface stratum thus 
affected is relatively small. 
