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 pu]se 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 Chlorophycece, Bacillariacece, chlorophyll- 

 bearing Mastigophora, Rotifera, and Entomostraca. The average 

 lag after the day of full moon for each of the groups, in the 

 order named, is 13.7, 14.8, 14.3, 13.1, and 14.3 days, re- 

 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 their 

 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*n-solution or suspension, 



