510 
emphasis laid upon the subject in connection with my discus- 
sion of the volumetric data will be found in the statistical data 
of Part II. of this paper. In this connection it may be noted 
that the statistical data of other investigators Jend some sup- 
port to the probability that this cycle movement in the plank- 
ton will be found to occur in other localities as well as in those 
examined by us. Instances suggesting this occurrence may be 
found in the statistical data cf Amberg (’00), Steuer (’01), and 
the more recent work of Cohn (’03). 
This cyclic movement consists in the repetition of rise and 
decline in production—a repetition broken in our records only 
by the imperfection of our data. Wherever collections are of 
sufficient frequency it is possible to trace it—sometimes, how- 
ever, only with the aid of statistical data—continuously through 
all the vicissitudes of changing seasons, of summer heat and 
winter’s ice, of the vernal rise and autumnal decline in tem- 
perature, and of high and low water. Moreover, it appears in 
all of our localities whenever collections have been made with 
a weekly, or even fortnightly, interval. 
These pulses vary in duration from 2 to 7 weeks, though 
the majority occur in limits of 3 to 5. Their amplitudes vary 
greatly, and are plainly influenced by various environmental 
factors. Their limits are also frequently modified by these 
factors, though the evidence is not clear that any of the envi- 
ronmental factors we have discussed are correlated directly 
with the cyclic movement itself. 
In the discussion of production in the backwaters the uni- 
versal approximation in time of these pulses in the various 
localities, or even their precise coincidence in many instances, 
was recorded. The cause of this tendency toward uniformity 
in the direction of movement in production in these various 
localities at the same time is not apparent from the data at 
hand. Contributory to it are the facts of a plankton largely 
composed of the same species of planktonts, of a connection 
and commingling of waters in all of the localities in flood con- 
ditions, and of the operation of environmental factors com- 
mon to all of the localities. 
