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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 ptilse 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. 



