285 
Illinois as compared with other streams, as shown by the 
slight ratio of development of the stream (see p. 102), tends to 
prevent the rapid mingling of channel and marginal waters, 
and thus gives cumulative effect to their differential charac- 
ters. 
In order to trace the quantitative effect of the shore and 
determine the variation in transverse distribution, | made two 
series of ten collections each along a transverse line, the first 
at our usual plankton station and the second below the mouth 
of Spoon River (see Pl. II.). The results of the first-named 
test, made August 26, 1596, are given in the following table, to- 
gether with conditions of distance from shore, depth, tempera- 
tures, and turbidity. The river at this time stood at 6.5 feet 
above low water, and had a width at the station of 150 meters. 
PLANKTON IN CROSS-SECTION OF RIVER AT STATION E. 
< a Tempera- Centrifuge Enumeration Omitting Omitting 
5 hie : ture > method method Nos. 1,9, 10} Nos, 1, 8, 9, 10 
Slag i=) (F.) >ES 
2 3) 5 7 Balis)-=| 
a RE BS > Sea | De: De- | Per m.3 |Under1sq.m. 
5 => |Plank | Par- DAN ee apes | ae ase 
= 8 8 5 Sur- | Bot- 5 4.2] ton in ene ae | ture ae Biss 
Hot=|¢ j x eA 
é g a] Q |face | tom | os emis sets tonts per from Vol-| ture | Vol- | ture 
A a ae in + res in + ©\ in = pins in + 
JI per ct perct per ct. 
1 10 1.68 82 77 .33 2.00 | +27.5 143,800 +318 3.36) 
2 37.5 3.96 73 nF T7 33 1.34 | —14.5 110,000 + 0.8 |1.34 |_224 Gg 31 | —25.2 
3 75 4.88 77.5 77 45 1.34 | —14.5 95,600 —12.4 |1.34 |—22.1 6.5 — 7.9 
4 85 4.88 77.5 a7 45 1.52 | — 3.2 110,200 + 1.0 1.52 |—11.6 7.42 | + 4.5 
5 | 95 [427 | m5] 77 | 45 | 144]— 86 | rox600 |+ 0.5 l144|—163 | 6.15 | tis 
6 105 4.04 77.5 7 42 2.36 | +50.5 93,100 —14.7 |2.36 |+37.2 9.53 | +34.2 
7 115 3.18 77.5 77.1) 40 2.40 | +53.1 112,500 J+ 3.1 |2.40 |4+39.5 | 7.63 | + 7.5 
8 125 1.68 a7.5 77.5) .40 1.64 | + 4.8 110,300 \+ 1.1 |1.64 |— 4.7 [2.76] 
9 135 1.22 77.75 77.5] .38 1.04 | —33.9 109,900 j+ 0.7 | 11.27] 
10 146 0.56 77.75| 77.6) .30 -60 | —61.7 96,200 |—1L8 [ .34] 
Average | 1.57] 27.21 109120 | +78 11.72] 21.9] 710 | £154 
The collections were made with the pump, one fourth of a 
cubic meter of water taken from bottom to surface being 
strained in each catch. 
The variation in the catches is much greater in the cross- 
section than in limited longitudinal tests, in accord with the 
greater contrast in environmental conditions. The marked 
decline near the western shore may be due to the marginal 
belt of vegetation then present along that side of the river, and 
