301 



Considering, then, the data from July to the end of the 

 year in 1895 (PL IX.), we find that the month closes at a min- 

 imum of .33 cm. 3 — 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 

 in the volumetric and 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 cm. 3 on August 

 24. The mean of the pulse,* that is the line 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 cm. 3 , 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. 



