em3 
Quiver ig E Phelps Lake, 
Fic. D.—Seasonal distribution of plankton production in vegetation-poor and 
vegetation-rich waters, based on the averages of the monthly averages for all years 
of collection. 
tion will be found in the individual collections recorded in 
Tables V. and IX. and VI. and VII., or in the monthly averages 
of the table following page 342. This striking contrast is still 
more enhanced by the statement of the monthly ratios of pro- 
ductivity in waters rich and poor in vegetation. These range 
from 1 to 1.5 in April to 1 to 20 in August. The fluctuations 
in the ratio are of themselves very significant. During the 
period from February to July inclusive the ratio is at its lowest, 
ranging from 1 to 1.5 to 1 to 7. Excepting only the month of 
July, this is the period of high water, in which the vegetation, 
if present, occupies a much smaller proportion of the volume 
of the lake, and is therefore to a proportionate degree restricted 
in its effect upon the plankton. Under such flood conditions 
these several localities are more or less merged in the general 
