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 
