310 
in most cases by the delimiting minima, the interval between 
maxima and that between minima, the date of the maximum, the 
deviation of the beginning and of the maximum of each pulse from 
the day of full moon, the deviation of the abscissa of the center of 
gravity of the polygon formed by the plot of each pulse, and the 
date of full moon. Deviations prior to the day of full moon are 
preceded by the minus sign. 
The average duration. between minima is 30.25 days and that 
between maxima is 29.97 days; the average location of the initial 
rise of the pulse is 5.1 days prior to full moon; and the average lags 
of the dates of maxima and abscissa of center of gravity of the 
polygon of occurrences are 11 and 10.45 days, respectively. The 
probable error of the location of the abscissa of a single pulse is + 7.5 
days, and of the average deviation of the abscissa only + 1.25 days. 
The table on pages 296-299 shows the lag of the maximum 
individual pulses of Chlorophycee, Bacillariacee, chlorophyll- 
bearing Mastigophora, Rotijera, and Entomostraca. The average 
lag after the day of full moon for each of the groups, in the 
order’ namied, is 13.7,.°14.8, 143, 13.) and 14:3 idaycuae 
spectively, with a grand average of 14.1 days for the 175 pulses 
listed. Of these pulses, 135, or 76 per cent., culminate prior to the 
third week after the date of full moon, and 94, or 52 per cent., in 
the fortnight between 7 and 21 days after full moon. The averages 
and percentages given in this paragraph vary but slightly from the 
demands of chance in favor of a hypothesis that the pulses tend 
to culminate in a particular part of the lunar month, though the 
data of the total chlorophyll-bearing organisms given above, es- 
pecially the deviation of the abscissa of center of gravity of the 
polygon of their occurrences, point in the direction of a lunar factor. 
There is no.doubt of the fact of recurrent pulses and of them 
distribution at intervals whose average approximates that of the 
lunar month, though their correlation with any particular part of 
the month is in no way constant and much less apparent. It would 
not be strange that the duration interval, or that the position of 
maxima and minima, should be subject to disturbance, to accelera- 
tion and delay, even to obliteration, in the fluviatile environment 
with its multitudinous factors,-—flood and drouth, summer and 
winter, clear and turbid waters, bright skies and overcast, the rise 
and fall of nitrates and other substances in solution or suspension, 
