147 
Owing to the confinement of flood waters within narrower bounds, 
all effects of greater depth and swifter flow of the stream must be 
intensified. The bottom sediments are now more forcibly scoured out 
and moved farther down-stream than formerly; the successive stages of 
the oxidation and assimilation of sewage proteids are carried farther 
downward, as is also the upper limit of the normal life of the stream; 
the plankton is transported more swiftly and continues a shorter time in 
the Illinois, multiplying there, consequently, to smaller numbers; and 
more of the food material of the Illinois escapes into the Mississippi 
unconsumed. 
Moreover, drainage of contributing lakes and swamps and narrowing 
of the area of overflow lessens the productivity of the river itself quite 
independently of the richness of its waters in the elements of fertility. 
A river and its plankton are a flowing soil and its crop, both slipping 
away continuously, but both renewed constantly from an exhaustless 
source of supply. The fertility of the flowing water at any time is not 
dependent on the fertility of that which has preceded it, but on materials 
of fertility brought into it from the watershed. A complete exhaustion of 
this flowing soil by “overproduction” would not impoverish, but would 
actually enrich the organisms depending on it, for they could avail them- 
selves of its entire product without penalty of subsequent starvation. 
As the plankton of a river system is carried down-stream, its progeny 
are carried with it, and, however numerous they may become, they can 
have no upstream effect on the population. If the running wafer were 
left wholly to itself, the river would speedily empty itself of plankton; to 
maintain the floating population there must be a constant source of supply 
outside the waters involved in the downward movement. Such a supply 
can be found only in places where aquatic organisms are virtually sta- 
tionary, or from which, to say the least, they do not escape until they 
have themselves begun to multiply, and in which, consequently, they will 
leave fertile descendants behind them. Such places of possible continuous 
origin of the plankton organisms are weedy waters along shore, sluggish 
shoals, eddies, bays, sloughs, open backwaters of the bottom-lands, and 
lakes connecting with the stream. The river plankton originates in the 
mere overflow of the stationary population in such breeding places, and 
the reduction of these sources of supply must have its proportionate 
effect on the river product. Hence, the plankton productivity of the 
stream does not depend primarily on the richness and extent of its own 
flowing waters, but on those of its subsidiary breeding grounds, and if 
these are not adequate to the maintenance of a plankton sufficient to 
consume all the readily available food materials of the stream, more or 
less fertility of the-current waters must go to waste. 
It is conceivable, of course, that stagnant and semi-stagnant tributary 
waters might be so productive and so extensive as to contribute to the 
river a rapidly multiplying population sufficient completely to exhaust the 
food supply borne by the running water within the limits of its own 
course, however fertile it might be, sending it out at the mouth of the 
