312 



concerned, in the last week of June. If, on the other hand, 

 we delimit the pnlse here as heretofore by minimum volumes, 

 we shall find its later limit to be July 6, giving it a total duration 

 from June 1, of 35 days. Its greatest amplitude, 1.68 cm.^, oc- 

 curs on the 11th, and its mean on the 14th — 29 days after that 

 of the joreceding pulse. With the exception of the first three 

 days this was a month of continuously falling river levels. 

 The large proportion of silt in the catches and the fluctuations 

 in the temperatures in the first ten days of the month suggest 

 flood water of recent origin. Nevertheless, the maximum pro- 

 duction of the pulse appears at the close of this disturbed peri- 

 od, a slight decline with little subsequent fluctuation in pro- 

 duction marking the remainder of the pulse. 



The average production in June, 1896 (.72 cm.^) is low in 

 comparison with that of 1898 (3.96), the only other year in 

 which the June production is sufficiently represented in our 

 records. In both of these years there was rapid and prolonged 

 decline from previous flood, but in 1896 the proportion of con- 

 tributions from impounded backwaters was much less than in 

 1898. Greater time for breeding plankton is thus afforded as 

 a whole in 1898, and greater production follows. The maxi- 

 mum production coincides with the maximum of nitrates 

 (PI. XLIIL), though it attends a depression in nitrites and free 

 ammonia. The general low production of this month occurs 

 in the presence of an unusual quantity of nitrates, so that one 

 at least of the important elements for production was not 

 lacking. 



The Juhj pulse has a duration of 19 days, — from the 6th to 

 the 25th, — with a maximum amplitude of 2.24 cm^ on the 20th. 

 Its mean also falls on the 20th — 36 days after that of the pre- 

 ceding pulse. This is a month of considerable hydrographic 

 disturbance, the total movement in levels being 7.7 ft. — a fall 

 from 5.2 to 2.5 followed by an interrupted rise to 7.3. The 

 pulse lies in the middle of this period and falls under the in- 

 fluence of both fall and rise. During the period of decline 

 the recovery of the plankton from its minimum of .26 on July 6 



