215 



vernal one both occur on the decline of the major floods of the 

 year, and that the relative proportions of the two floods are to some 

 degree paralleled by the amplitude of the pulses of Synch&'ta which 

 attend their decline. The effect of the impounding backwaters as 

 reservoirs for the greater development of the plankton is suggested 

 by these data. 



Following the midsummer minimum is an autumnal pulse whose 

 amplitude and location alike are subj ect to much variation. As will be 

 seen in the table on pages 213 and 214, the maximum jmtumnal pulse 

 is located twice in October, twice in November, and once in Decem- 

 ber. This may be due to the fact that the collections are insufficient 

 in some of the years, or to the probability that any one of several 

 recurrent autumnal pulses may be the major pulse of that season. 



An examination of the seasonal distribution. in 1898 (Table I.) 

 and of the location and temperatures of the pulses recorded in the 

 table on pages 213 and 214 will suffice to demonstrate the capacity of 

 this species to develop at all temperatures within the seasonal range. 

 The largest pulse (1,139,000 on May 3, 1898) is at 60, and the next 

 in size (1,121,056 on December 11, 1895) is at 32. It will, however, 

 be seen in the two tables that the pulses and the numbers in general 

 during the periods of maximum heat and cold are not so large as in 

 the intervals of more moderate temperatures. The impetus of the 

 autumnal development may carry some of the pulses over in to 

 minimum temperatures, but the level of development declines 

 thereafter. There is thus something of a tendency for the average 

 temperature of the larger occurrences to approach the average 

 temperature of the year. 



The number of pulses listed in the table on pages 213and214is38. 

 Of these, 34 fall within the period included in Plates I. and 1 1. of the 

 pulses of chlorophyll-bearing organisms. Of the 34 there are 18 

 which coincide in location with these plant pulses, 12 which follow 

 at a brief interval, and 4 which bear no such relation, three of the 

 last being minor winter pulses. 



The dependence of the recurrent periods of rapid multiplication 

 of Synchata the most abundant rotifer of the plankton upon the 

 rhythmic increase of the food supply is thus fairly demonstrated. 

 The coincidence of the pulses of Synch&ta with those of the total 

 Ploima is readily seen in Table I., and is equally apparent in prior 

 vears. 



