. Bulletin of the Illinois State Laboratory of Natural History . ions representative of our environment. These testswere not carried beyond this point, since we had adopted thepumping method for the later and major part of our work. 263 In this method the question of coefficient is entirely eliminated. The results of these tests are given in the preceding table. The variation in the coefficient w^ith different seasons, lo-calities, and planktons is apparent upon the first glance atthe table. The greater straining capacity of a new net as com-pared with one which had been used for some time may
. Bulletin of the Illinois State Laboratory of Natural History . ions representative of our environment. These testswere not carried beyond this point, since we had adopted thepumping method for the later and major part of our work. 263 In this method the question of coefficient is entirely eliminated. The results of these tests are given in the preceding table. The variation in the coefficient w^ith different seasons, lo-calities, and planktons is apparent upon the first glance atthe table. The greater straining capacity of a new net as com-pared with one which had been used for some time may be seenin the tests made June 16, and July 9, 11, and 21, 1896. Thenew net—the silk in which had been shrunken by washing andpressing several times prior to use—catches at least 50 per cent,more than the old one which had done service since February 25. The rise in the coefficient as the net progressively clogsby plankton is demonstrated by the tests of October 14, 1899,and July 27, 1897. The latter test is graphically presented inthe accompanying l^ 10 5 0-m. Fig. B. —Catches of plankton made on 30-meter haul by drawn net and pumpThe upper, continuous line represents the pump catch; the middle, dotted line thecatch of the net measured by the settling method; the lower, heavy line the samemeasured by the centrifuge. *T» . __ .— T->_ \T__n X- ^^^.. \ar,^ ..^.»^ Date Locality, etc. of haul ^^* Haul Gravity Method—24 hrs. Centrifuge Enumeration—I m. water Plankton. Net |Pump|Coefficient Net IPump Coefficient Net 1 Pump iCoefficient 1895Oct. II Illinois River 30 m. 2 I 175 -475 -075 .215 37,771 57,931 Some silt. Sjynura and Copepoda. Dec. 30 Illinois River 30 m. 2 I .160 .760 .080 .350 119,150 243,181 Much silt. Synura, Syiichata, and Copepoda. 1896 30 m. 444 I2av. . 3-617 .140 . . .... 3-333 141,490 84,160 112,830 Small
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectnatural, bookyear1876
