339 
uary, and to the repeated flushing of the stream in the preced- 
ing autumn. The plankton was not therefore diminished by 
the change in chemical conditions which had progressed up to 
the time of the sudden rise on the 23d. The average produc- 
tion for the month (.81 cm.*) is the largest recorded in any 
year. Production reaches on the 21st the unparalleled midwin- 
ter level of 1.92 cm.*—an amount in excess of any production 
in-July-November of the preceding year. This is due, it 
seems, to the stable conditions attending the decline of the 
January rise, to the high levels which permitted some access of 
plankton from backwater breeding grounds, and to the freedom 
from stagnation. The near approach of this condition is, how- 
ever, revealed by the direction of the changes in chemical con- 
ditions, but its arrival was prevented by the almost equally 
catastrophic invasion of the sudden flood of the 25d, which re- 
duced the plankton content to a minimum of .07 em. on the 
28th. Plankton production of this volume at approximately 
freezing point, equaling that at the sammer maximum in July, 
is a Striking instance of the adaptation of the plankton to the 
extremes of temperature. 
The March pulse has a duration of 28-++ days,—from Feb. 28 
to Mar. 28-++,—with a maximum amplitude of. 54 em.’ per m.* on 
the 7th. Its mean falls on the 12th, 20 days after that of the 
preceding pulse. In the first week the rise of the last of Feb- 
ruary ceased at 13 ft., affording overflow of all but the highest 
bottoms. Levels continued to fluctuate between 15 and 14 ft. 
during the remainder of the month, so that we have here a 
month of sustained overflow with repeated additions of storm 
water. The sewage and organic materials carried into the 
stream with the first access of flood waters decline rapidly dur- 
ing the month, as is seen (Pl. XLV.) in the rapid and consider- 
able decline of chlorine, oxygen consumed, free ammonia, and 
organic nitrogen. Temperatures rise but 5° during the month, 
and the average for the month is from 5° to 10° lower than that 
in other years. The reduction in production with the initial flood 
and the thrice-repeated influx of storm water, combined with 
