451 



waters. Production is deficient in vegetation-rich backwaters 

 (Quiver Lake) and in excess in open reservoir lakes (Thomp- 

 son's Lake). 



1896. A year of recurrent floods of moderate height and 

 greatly diminished production in channel waters. The repeated 

 summer invasions of the vegetation-rich backwaters by flood 

 destroyed and removed much of the season's growth, and we 

 find this the year of greatest plankton production in these areas 

 (Quiver, Dogfish, and Flag lakes). The more open waters, poor 

 in vegetation (Thompson's and Phelps lakes), have vernal 

 pulses of considerable magnitude, but as summer and autumn 

 production is not up to the average there is as a whole a defi- 

 ciency in these areas. 



1897. A year of prolonged winter-spring flood, followed 

 by continued and abnormally low water in the last 5 months 

 of the year. The early flood apparently reduces production 

 everywhere, while the prolonged low levels lead to abnormally 

 high production in the channel and in vegetation-poor back- 

 waters (Phelps and Thompson's lakes). In Quiver Lake the 

 relative dominance of vegetation and tributary waters of recent 

 origin is so increased that production falls to a low level. Even 

 tributary streams (Spoon River) so decline in run-off in the 

 low-water period that an abundant plankton develops in their 

 waters. 



1898. A year of normally located spring floods, followed 

 by repeated minor flushes in summer and autumn. There 

 is a meteoric but normally located vernal pulse, with a low 

 level of production throughout the remainder of the year in 

 the channel and in backwaters intimately connected with it 

 (Quiver and Thompson's lakes), and an abnormally high and 

 well-sustained level of production in backwaters isolated from 

 flood contact and free from vegetation (Phelps Lake). 



The different localities may be briefly characterized as fol- 

 lows. 



Illinois River. Channel waters contain a plankton which 

 in constituent organisms, character of the course of production, 



