515 



prairies. Its waters are discharged into the upper end of the 

 eastern arm of Quiver Lake, and are impounded for a varying 

 length of time before reaching the river. No channel defined 

 by the configuration of the bottom traverses the lake, and since 

 its area is relatively large in comparison with the discharge of 

 Quiver Creek, the tributary waters are subject to considerable 

 impounding when the lake is free from vegetation. When, 

 however, vegetation is abundant, a fairly well-defined channel, 

 through which the discharged waters make their way with per- 

 ceptible movement, is kept open through the matted growths. 

 The impounding period is thus reduced for the channel water 

 under such conditions. 



Collections were made in Quiver Creek, near Topeka, 111., 

 above McHarry's mill-pond, from September 1, 1896, to April 

 20, 1897, at intervals of ten days, by Mr. W. R. Deverman, who 

 kindly volunteered this service for the Station. A tow-net of 

 No. 20 silk was used, but no exact quantitative method was 

 adopted, so that these collections are available only for quali- 

 tative comparisons. 



The catch consisted largely of silt in the form of quartz 

 grains and coarsely comminuted vegetable debris, with rela- 

 tively few plankton organisms. 



The several catches were uniformly diluted, and the plank- 

 ton organisms counted in a uniform fraction of a cubic centi- 

 meter of the dilution from each catch. The various species 

 detected and their monthly averages in numbers are given in 

 the appended table. The figures have but slight quantitative 

 value, though they will serve to illustrate in a general way the 

 composition of the plankton and its seasonal changes, and will 

 also afford a sufficient basis for a comparison of the constituent 

 organisms of the plankton of Quiver Creek, Quiver Lake, and 

 the river, though not for a comparison of their relative num- 

 bers per cubic meter in each of the three situations. 



The plankton of Quiver Creek, as shown in the table, may 

 be characterized as largely tycholimnetic, that is, composed of 

 littoral species, shore-loving and bottom forms. This is seen 



