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vations about Havana, and upon the conditions observed during 

 a trip made in May, 1899, by the courtesy of the Illinois State 

 Fish Commission, upon the steamer "Reindeer," from the mouth, 

 at Grafton, to Hennepin, 211 miles above. As a rule, the river 

 is quite free from vegetation. There is, to be sure, in the upper 

 part of Peoria Lake, which is merely an expanse of the river 

 (PL I.), an extensive area which is permanently occupied by 

 aquatic plants. A similar expansion known as Havana Lake 

 (PL II.) is also at times abundantly supplied with vegetation 

 in its shoaler and quieter portions. There are also springy 

 shores, usually of gravel or sand, located where the channel 

 encroaches upon a bluff upon which a permanent littoral veg- 

 etation is maintained regardless of river levels. Generally, 

 however, the water reaches the steep or sloping bank of black 

 alluvium without any fringe of green. There are scattered 

 Lemnacece — principally Spirodela polyrrhiza and Lemna minor, 

 with Wolffia braziliensis and columbiana — floating with the cur- 

 rent from spring till late in the fall. Patches of "moss" con- 

 sisting of Ceratophyllum demersum are also floated into the chan- 

 nel from flooded backwaters, or loosened by fishermen's seines 

 and then carried by the current from backwaters or the shores 

 of the river into the channel. On some protected shores where 

 the current is slight the arrowleaf {Sagittaria variabilis) main- 

 tains a foothold — as on theeastshore, just above the "to'whead" 

 (PL II.). A small patch of Potamogeton pectinatus also remains 

 year after year in the river in the rapid currents that rush 

 through Quiver cut-off (PL II.). Such instances of permanent 

 vegetation are, however, of rare occurrence, and form but insig- 

 nificant factors in the immediate environment of the river 

 plankton. 



A temporary fringe of vegetation has appeared along the 

 river margins when relatively low-water stages prevailed in the 

 spring and were maintained without marked floods until sum- 

 mer, as in 1894 and 1895. This littoral growth is not composed, 

 however, of the permanent littoral flora, such as the arrowleaf, 

 the Polygonums, and the rushes, but is like that found in deeper 



