627 



ness of vegetation. Emergent Nelumbo lutea Pers., with leaves, flowers, and seed 

 pods. Submerged Ceratophyllum demersum L. Taken in low water of summer of 

 1894. 



Plate XVIII. 



Dogfish Lake, looking northeastward, in low-water summer conditions. Lake 

 full of Ceratophyllum, Elodea, and Potamogeton. Plankton station (L) near center 

 of lake. 



Plate XIX. 



Flag Lake in autumn of 1895 at plankton station (K), looking north-northeast- 

 ward. Scattered dwarfed clumps of Scirpits and an abundance ol Nympha>a consti- 

 tute the principal vegetation in this open area. 



Plate XX. 



Thompson's Lake from shore station (G), looking southwestward, in low-water 

 conditions of midsummer. Lotus bed in distance, and broad belt of submerged veg- 

 etation, principally Ceratophyllum, along shore. Plankton station (G) in open water 

 to the right (northward). 



Plate XXL 



Phelps Lake, looking southwestward from plankton station (F), in midsummer 

 in 1894, just as the lake was drying up. 



Plate XXII. 



Seasonal distribution of plankton in Spoon River (Station M) in 1896. Scale of 

 plottings of plankton 0.1 cm. 3 per vertical unit, instead of 1 cm. 3 , as in case of all 

 other stations. Dotted portion of ordinant indicates estimated proportion of silt 

 in total catch. Thermograph plotted from surface temperatures of water at times 

 of collection of plankton, and hydrograph from gage-readings in the adjacent Illinois 

 River at Havana. Ice indicated by black areas below diagram, 1 mm. equaling 6 

 cm. of ice. 



Plate XXIII. 



The same for 1897. The excess of plotted plankton-silt ordinants over limits 

 of diagram is indicated by figures at top. 



Plate XXIV. 



The same for 1898-1899. 



Plate XXV. 



Seasonal distribution of plankton in Quiver Lake (Station C) in 1894. Scale of 

 plotting of plankton-silt is 0.4 cm. 3 per vertical unit. Hydrograph is that of the Illi- 

 nois River at Copperas Creek. Thermograph is that of surface temperatures at 

 times of plankton collections. 



Plate XXVI. 



The same for 1895. Hydrograph from Jan. 1 to Aug. 8 is that of the Illinois 

 River at Copperas Creek, and thereafter, from river gage-readings at Havana. 



Plate XXVII. 



The same for 1896. Hydrograph from gage-readings in the Illinois River at 

 Havana. 



