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the fluctuating access of sewage and industrial wastes, the continuous 
current, the ever-shifting population and the never ceasing struggle 
for existence and continuance on the part of the interrelated organ- 
isms of the plankton and of the shores and bottom. The wonder 
is that any single factor of the environment, however constant, 
could make any orderly impression in this chaotic situation. 
This fact that the average interval of the pulses of the phyto- 
plankton is so nearly the lunar interval would seem to indicate 
some causal nexus between the two phenomena. An attempt to 
correlate the plankton pulse with any particular part of the lunar 
month is, however, less conclusive. The interval of collection, one 
week, is so great that the course of the pulse can be traced only 
approximately, since its beginning, maximum, and end can only, 
from our data, be located at one of these intervals, and more or 
less distortion results therefrom. Again, the large error in the 
plankton method may be responsible for some of the fluctuations 
in the data. Still more potent, probably, are the various factors 
of the environment of the plankton which combine with the lunar 
illumination to produce resultants which divert the pulse more or 
less from the course which the undisturbed lunar factor would 
cause it to take. Evidence in favor of this view appears in the 
fact that the greatest disturbances in the rhythmic sequence of 
the pulses are wont to occur in winter months, when floods, ice, 
and cloudy weather tend most to interfere with the full action of 
the lunar factor, while the correlation of full moon and phyto- 
plankton pulse is most intimate in the stable conditions of summer. 
_This is seen in the fact that the average of the average monthly 
lags for all of the May—August pulses is 11.9 days, and for the 
remaining eight months, 18.2 days. 
The subject here presented is one which lends itself readily to 
field and laboratory experiment, and it is to be hoped that the sug- 
gestions of a correlation between the plankton pulses and lunar 
cycle here made, will be put to the test of further quantitative and 
statistical, as well as experimental, tests in controlled environments 
where the disturbing factors of the fluviatile environment are elimi- 
nated. 
