498 
A comparison of these two lakes indicates more nitrates in 
Quiver than in Thompson’s (.68 to .53 parts per million)}—a 
phenomenon which may be explained by the proximity of the 
former to the river and the greater invasion by its richer (.81) wa- 
ters. In the matter of free ammonia Thompson’s Lake is much 
the richer (.352 to .138 parts per million), though it falls con- 
siderably below the river (.95) in this particular. The striking 
feature of the diagrams and tables is the marked reduction in 
nitrates and free ammonia during the period of growth, from 
June 1 to October 1, in both lakes as contrasted with that of 
quiescence, from October 1 to June 1. The former period is 
one of higher temperature and less flood water, thus favoring 
the process of decay and the concentration of its products. The 
marked decrease in both the free ammonia and nitrates during 
this period may be explained by the utilization of these prod- 
ucts of decay by the chlorophyll-bearing organisms, which 
presumably are much in excess of those of the colder period. 
In Thompson’s Lake the phytoplankton would be the principal 
consumer, while in Quiver Lake submerged vegetation assumes 
this role. The uniformity in the nitrates throughout this period, 
and the reduction to a similar amount (about .2 parts per mil- 
lion) in both lakes are significant of some sort of an equi- 
librium between the supply furnished by decay and its utiliza- 
tion in the growth of plants. This phenomenon of reduction 
of nitrates to a summer equilibrium is to some extent manifest 
in the analysis of soil waters (see Palmer, 97), and may in like 
manner be attributed to utilization of the nitrates by vegetation. 
At first thought the volume of submerged vegetation seems 
large in comparison with that of the phytoplankton, which it 
replaces ; but when the permanence and persistence of the con- 
stituent cells of Ceratophyllum are contrasted with the many 
generations of the algae and diatoms of the plankton which 
arise during a season’s growth, the difference is less evident. 
Furthermore, a much greater proportion of the cells of the 
phytoplankton contribute directly to the growth of the animal 
life of the lake. 
