25 
vernal one both oceur 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 Syncheta 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 subject tomuch variation. Aswill be 
seen in the table on pages 213 and 214, the maximum autumnal 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 213 and 214 is 38. 
Of these, 34 fall within the period included in Plates I.and II. 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 Syncheta—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 Syncheta with those of the total 
Ploima is readily seen in Table I.,and is equally apparent in prior 
years. 
