154 



ing from the decaying and matted stems of the preceding sum- 

 mer. Turning back towards the river we pass through the 

 heavy timber where the still brown water, cool and clear, over- 

 lies the decaying leaves and vegetation of last season's growth, 

 now coated with the flood deposits of the winter. Emerging 

 again upon the river channel we may find a turbid yellow flood 

 pouring out from Spoon River, bringing down its load of drift 

 and earth, and marking its course down the stream as far as 

 the eye can see. 



From an environment even more varied than this come 

 the different contributions to the plankton of the river in the 

 flood seasons. Every change in level modifies this environ- 

 ment by connecting or cutting off backwaters, shifting or check- 

 ing currents, disturbing vegetation and temperature in a man- 

 ner the very complexity of which beggars description. 



Contrast with the extent and variety of conditions at flood 

 the limitations placed upon the stream at low water (PI. IV. 

 and V. ). Instead of an unbroken expanse of four or more miles 

 we find now a stream only 500 feet in width (at Station E), while 

 the adjacent territory is dry land save where the sloughs, 

 marshes, and lakes remain as reservoirs. Quiver Lake is now 

 much reduced in width, and it may be choked with vegetation 

 except in a narrow channel where the clear water shows little 

 or no current. A half mile below we find the river water rush- 

 ing in a narrow " cut-off " across the ridge of black alluvium 

 into the lower end of the lake. The wooded banks which sep- 

 arate the river from Quiver and Seeb's lakes are now crowded 

 with a rank growth of weeds and vines. The latter " lake " is re- 

 duced to a shallow stagnant arm of the river, whose warm turbid 

 waters are foul with dead mollusks, and whose reeking mud- 

 flats beneath the August sun shine green and red with a scum 

 of Euglena. As we pick our way through the tangle of rank 

 vegetation we come upon Flag Lake, now a sea of rushes. The 

 discharge from this marsh to the river ceased in the early sum- 

 mer, and its margins are even now dry, with gaping cracks. 

 Beyond the marsh we pass to the shore of Thompson's Lake to 



