246 
aquatic flora characteristic of the backwaters of the Illinois 
River bottoms. The regions occupied by aquatic vegetation 
(Pl. II.) are of considerable extent even at low-water stages, 
and increase rapidly in area at higher river levels. The diver- 
sity of the aquatic flora is most pronounced at the moderate 
stages of water (3 to 6 feet above low water) which often pre- 
vail after the decline of the spring flood during early summer. 
A characteristic littoral flora is found along the firm san- 
dy margin of the eastern side, and ona few points of similar 
soil which project from the western bluffs to the lake. Jun- 
cacee and the shore-loving grasses and sedges abound here, and 
as the shores emerge the bottom-land Composite and Polygo- 
nums encroach upon their domain. In other regions the 
slope is more gradual and the shore line, as the water recedes, 
moves Over wide stretches of alluvial soil, often of slight con- 
sistency, to a considerable depth. Here the vegetation is more 
luxuriant, and Polygonum amphibium, the arrowleaf, and the 
water-lily vie with the big river rush (Scirpus fluviatilis) for a 
foothold in these regions, exposed only at lowest levels and 
never baked hard by the midsummer’s drouth. 
At higher levels is found a varied mixture of semiaquatic 
and upland genera, such as Lippia, Bidens, and Polygonum, with 
coarse grasses and sedges. Inside of this varied littoral zone is 
founda permanent flora of almost equal diversity. Along 
sandy shores we find a belt of more or less open vegetation con- 
sisting largely of Potamogeton natans, Klodea, Nais, and a few 
Juncacee, with scattered lilies and lotus. At the southern end 
of the lake there is an area over a mile in length occupied 
mainly by Scirpus lacustris, great beds of lotus and water-lily, 
and mats of Lemnaceew. A narrow belt with less of the Scinpus 
is found along the alluvial margins of the western shore, and 
scattered patches occupy the shoals that connect the northern 
end of the lake with the swamps that lie to the northward. 
In the deeper waters Ceratophyllum takes possession in some 
regions to the practical exclusion of all other species save a few 
Potamogetons and some scattered Hlodea. The region in which 
