301 
Considering, then, the data from July to the end of the 
year in 1895 (Pl. [X.), we find that the month closes at a min- 
imum of .383 cm.’—the end of a pulse of uncertain limits and the 
beginning of the next, which culminates in the third week of 
August. This August pulse is followed by one of less ampli- 
tude and duration, culminating about three weeks later, by 
one of slight amplitude in October, culminating at an interval 
of about four weeks , by one of greater amplitude in November, 
after an interval of about five weeks, and by one in December, al- 
so of considerable amplitude, at an interval of about four weeks. 
The fluctuations of some of the component groups of organ- 
isms are shown in Plate LI., and considerable correspondence 
inthe volumetricand statistical pulses will be apparent on com- 
parison. 
The August pulse has a duration of 39 days,—from July 29 
to Sept. 9—and a maximum amplitude of 7.63 em.‘ on August 
24. The mean of the pulse,* that is the lime upon which the 
center of gravity of the polygon formed by connecting the ordi- 
nants lies, falls upon August 22. This pulse occurs in a period 
of somewhat stable low water, and its decline from the maxi- 
mum of 7.63 reaches 2.07 on Sept. 4 and occurs without the 
assistance of flood waters. On Sept. 5 a sudden minor flood, 
due to local rains, flushes the stream and completes the deple- 
tion of the plankton to .69 on the 7th. The August average for 
1895, 4.03 em.*, is higher than that of any other year excepting 
1894, in which but a single collection was taken, which may 
not be representative of the whole month. Freedom from ris- 
ing flood waters in 1895 is doubtless one cause conducing to 
this high average of production. The enriching effect of the 
minor flood which culminated in the closing days of July may 
also contribute to this end. The absence of rises in May and 
June would also tend to increase the contributions of organic 
material to the stream by this July flood as compared with 
*The mean was computed by multiplying the volume of each catch in the pulse 
(ordinant) by the number of days from preceding minimum to date of collection 
(abscissa) and dividing the sums of the products by the sum of the catches in the 
pulse, the quotient being the abscissa of the mean. 
