EXPLANATION OF PLATES.* 
PLATE I, 
Map of the Illinois River Basin, modified from a map in Cooley's “ Lakes 
and Gulf Waterway,” facing p. 58. Boundary of catchment-basin of whole system 
shaded, those of individual tributaries marked by dotted lines. 
PLATE II. 
Map of field of operations of the Illinois Biological Station at Havana, III., 
1894-1899. Locations of plankton stations in Illinois River (E), Spoon River (M), 
Quiver Lake (C), Dogfish Lake (L), Flag Lake (Ks), Thompson’s Lake (G), and Phelps 
Lake (F). 
PLaTE III. 
Illinois River bottoms at high water in spring flood in March, 1898, looking 
westward. River gage about fifteen feet above low-water mark. Taken from base of _ 
the eastern bluff, just below field headquarters (see Plate II.) on Quiver Chute. En- 
tire bottoms submerged, Quiver Chute and Illinois River united, Seeb’s Lake show- 
ing dimly through the forest on west side, beyond this the broad expanse of Flag 
Lake, with low forest intervening between it and Thompson's Lake. Western bluff 
visible. 
PLATE IV. 
Illinois River at low water during summer of 1894. Taken from same point as 
Plate III. River gage about 2 {t. above low water, showing minimum levels since 
erection of dam at LaGrange. Mud spit between Quiver Chute and Illinois River 
exposed. Summer foliage and atmospheric conditions obscuring bottom-land waters 
to westward. 
PLATE V. 
West bank of Illinois River a short distance below plankton station, looking 
northeastward. Taken during low water in midsummer of 1894. Sloping shore of 
black alluvium covered by low vegetation. Narrow marginal belt of vegetation visi- 
ble. River about 4oo feet in width. 
Prate, Vile 
Sun-spots, rainfall, and riverlevels. Upper section of figure taken from Lockyer 
(or). Middle section gives fluctuations in average rainfall in Illinois above and be- 
low the mean, as givenin records of U.S. Weather Bureau. Lower section gives 
fluctuations in mean annual river levels, compiled from records at Copperas Creek 
dam, 1878-1899. Average of all annual means shown at the left. 
* Plates IV., XV., XVII., and XXI. are from the Biennial Report of the Director of this 
Laboratory for 1893 and 1894; plates II., V., VIII., XVIII., XIX., and XX., from that for 1895 and 
1896 ; and plates III. and XVI., from that for 1897 and 1898. 
