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, 111., 

 1894-1899. Locations of plankton stations in Illinois River (E), Spoon River (M), 

 Quiver Lake (C), Dogfish Lake (L), Flag Lake (K), 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 ft. 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 400 feet in width. 



Plate VI. 



Sun-spots, rainfall, and riverlevels. Upper section of figure taken from Lockyer 

 ('01). Middle section gives fluctuations in average rainfall in Illinois above and be- 

 low the mean, as given in 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. 



