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aquatic flora characteristic of the backwaters of the Illinois 

 River bottoms. The regions occupied by aquatic vegetation 

 (PI. 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 on a few points of similar 

 soil which project from the western bluffs to the lake. Jun- 

 cacece and the shore-loving grasses and sedges abound here, and 

 as the shores emerge the bottom-land Compositm 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 

 found a permanent flora of almost equal diversity. Along 

 sandy shores we find a belt of more or less open vegetation con- 

 sisting largely of Potamogeton nutans, Elodea, Nais, and a few 

 Juncacece, 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 Lemnacece. A narrow belt with less of the Scirpus 

 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 Elodea. The region in which 



