627 
ness of vegetation. Emergent Ve/umbo 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 Scé7fus and an abundance of Vymphea 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 Cevafophy//um, along shore. Plankton station (G) in open water 
to the right (northward), 
PLATE XXI. 
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 o.1 cm.‘ per vertical unit, instead of 1 cm.‘, 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 I[|linois 
River at Havana. Ice indicated by black areas below diagram, I 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.’ 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. 
