294 



the data where collections are of sufficient frequency to adequately 

 delineate the curve of production, that is from July, 1895, to Oc- 

 tober, 1896, and from July, 1897, to March, 1899, a total of 37 

 months, and suggestions of a like phenomenon appear in the less 

 complete data of other years. The degree of agreement indicated 

 in the pulse of July, 1898, will be found, on examination of the data 

 in Table I. and in the plates of this paper, to vary with the environ- 

 mental conditions. Times of rapid change in hydrographic condi- 

 tions or in temperature generally show less agreement, and more 

 stable conditions will exhibit an equal or even greater uniformity 

 in the prevalence of the pulse-like rise and decline of the component 

 organisms. 



In order to show the course of these recurrent pulses in the 

 chlorophyll-bearing planktonts, the total Chlorophycetz, Bacil- 

 lariacecE, and chlorophyll-bearing Mastigophora on the one hand, and 

 of the Rotifera and Entomostraca (''Crustacea" of the plates), I have 

 presented the data graphically on Plates I.-IV., and in the table on 

 pages 296-299 have drawn up a list of the pulses, indicating the 

 dates of the collections which in the main enter into the respective 

 pulses, and the dates of the maxima or culminations of the five 

 groups named. Owing to the irregularities in the data, there are 

 some instances in which several possible dates might have been 

 chosen. Reasons for the choice are in several important instances 

 given in the foot-notes 'to the table. 



It is evident from the data here presented in graphic and tabular 

 form that the pulses of the five groups of organisms tend in the main 

 to coincide. This is shown in Plates I.-IV., and in the fact that the 

 average divergence of 175 group pulses listed in the table is 6.4 

 days, or, if 5 aberrant instances are omitted, only 4.8 days. In other 

 words, the pulses of the totals of the 5 groups included in the table 

 culminate on an average within an interval of 6.4 (4.8 in 170 cases) 

 days. The average of the extreme limits between maxima of 

 group pulses in the 36 periods of movement listed in the table is 

 11.7 days. 



It is apparent that the pulses would be more completely de- 

 lineated by collections at daily intervals, but even in the somewhat 

 irregular and at times chaotic data here presented, the evidence 

 seems conclusive that the seasonal production of the dominant 

 species and groups of planktonts tends to fall into coincident 



