449 
the average ratios found by Kofoid* to hold between silk-net and filter- 
paper volumes in 1896—1899, show a figure for the twelve-month period 
(200,477 tons) almost exactly treble the amount (67,750 tons) that was 
carried in the average year just prior to 1900. Of the twelve months’ 
total about 89 per cent. (179,916 tons) was accounted for during the 
four months of the spring season, March to June inclusive, during which 
period 1,474 tons passed every twenty-four hours. The 14,025 tons that 
passed during the five months July to November inclusive, made up only 
6.9 per cent. of the total for the year, but this amounted to ninety-one 
tons every twenty-four hours, and was enough if all settled to the bot- 
tom to supply 1,698 pounds per acre for every acre in the river below 
Copperas Creek dam at the average gage of that season and year (7.8 
ft., Havana). The December—February plankton (6,536 tons) was less 
than half that of July—November, and only 3.2 per cent. of the total. 
The full twelve months’ total, over 400,000,000 pounds, amounted to 
24,279 pounds per acre for each acre of the approximate acreage in the 
river below Copperas Creek dam at recent under-bank-full stages (8 ft., 
Havana); or to nearly a hundred times the wet weight of the total 
bottom-fauna stocks of July—October, 1915, shells deducted, between 
Copperas Creek and Grafton (4,277,351 pounds). The dry weight of 
this plankton at two to five per cent. (8,000,000 to 20,000,000 pounds) 
was twenty to fifty times the estimated dry weight (at 10 per cent.) of 
the total bottom stocks of 1915 below Copperas Creek (427,735 pounds). 
Complete figures for the plankton stocks produced in the full 120 
miles between Havana and Grafton would doubtless also include, in ad- 
dition to the Havana figures, new stocks of no small size added on the 
way down stream, both as a result of normal multiplication and lake and 
other backwater contribution. I do not take the fact that all of our 
down-stream plankton series between 1899 and 1910 showed a large de- 
crease in volumes southward of Havana as ruling out the inference of 
continued though hidden increase, at a rate merely slower than the rate 
of decrease due to consumption and settling. The average time of pas- 
sage between Havana and Grafton was 6.7 days at the average gage of 
July—November, 1909 (7.81 ft., Havana), and was 4.82 days at the 
average gage of March—June (Havana, 12.04 ft.). During upward 
pulses, rates of increase in plankton volumes (c.c. per m*) were several 
times recorded both by Kofoid and the writer for the river channel at 
Havana and for Thompson Lake, both in spring and autumn months, 
1896—1910, that amounted to over 25 per cent. in one day; while in ex- 
treme cases the increases ran to 60 to 70 per cent. in a single day, or 
400 to 500 per cent. in a week. 
* Bul. Ill. State Lab. Nat. Hist., Vol. VI., Art. II. 1903, pp. 552-554. 
