455 
is the unique factor which more than any other differentiates 
it from lake plankton. Toaless degree it seems to differentiate 
this aquatic environment from other streams, as a result 
largely of the imperfectly developed flood-plain, and conse- 
quent- unusual proportion of reservoir backwaters. 
It is, moreover, an exceedingly variable factor, operating 
with almost constant change in each locality, and from season 
to season in the same locality. Itisthis element of fluctuation 
and the resulting chaos in the movements of production which 
particularly characterize the river as a unit of environment, 
and ina Jarge measure differentiate it from the more stable 
lake. The changes depend primarily upon the unequal distri- 
bution of the rainfall and its run-off and the consequent fluctu- 
ations in levels with attendant changes in area, depth, condi- 
tions of ingress and egress of water in any given area, current, 
and age of the water. 
The effect of the area of the body of water upon its plank- 
ton production in our situation is so masked by combination 
with other factors that the available data are inconclusive. 
Our largest vegetation-poor backwater, Thompson’s Lake, pro- 
duces less (8.26 em.*) than the smaller one, Phelps Lake (22.55 
em.°). On the other hand, the largest vegetation-rich area, Flag 
Lake, produces 9.23 em.’—considerably more than the smaller 
Quiver and Dogfish lakes, 1.75 and 3.16 em.’—and these differ- 
ences are, moreover, in all probability to be attributed to other 
factors than mere area. 
The relative development of the shore-line isa corollary of 
the form of the body of the water, and is thus related to its 
area. In the case of the river, the development of the shore- 
line, as shown on page 284, is 78.3—a disproportionately large 
element in the environment of the plankton. 
This factor of area has been introduced here in order to 
emphasize the fact that mere size in itself has apparently little 
to do with plankton production. Plankton is present in smal] 
as well as large bodies of water, with, of course, an increasing 
proportion of littoral influences as areas contract. Within 
