436 



PLANKTON PRODUCTION IN li 



Station 



Illinois River 



Spoon River 



Quiver Lake 



Dogfish Like 



Flag Lake 



Thompson's Lake. 

 Phelps Lake 



i^h 



- 1-44 



0.30 

 0.91 

 3.33 

 2-73 

 9-03 



*The minus sign signifies below average and the plus sign above. 



While in 1895 production in the channel waters was both 

 absolutely and relatively high, yielding the highest monthly 

 mean (5.91 cm.^) in our records, and exceeding production in 

 the adjacent backwaters in 15 out of 27 monthly averages avail- 

 able for comparison (see table on p. 482), in 1896 we find the op- 

 posite extreme in production in these particulars. 



In the first place, the mean production as seen in the mean 

 of the monthly averages, 1.05 cm." per m.^or, in average of all 

 collections, 1.16 cm.^ (see table on p. 429), is the least observed 

 in our years of record. This is 61 or 47 per cent., according 

 as we base computations upon means of monthly averages or of 

 all collections, below the mean production in the Illinois. This 

 ensues from the catastrophic effect of recurrent floods which 

 periodically flushed the channel (PI. X.), sweeping away the 

 plankton-rich contents of the stream and replacing them with 

 barren silt-laden flood waters of recent origin. There are 6 

 major and 5 minor flood culminations in this year, and most of 

 them are marked by abruptness in rise, a factor which added to 

 their destructive effects. The total movement in river levels 

 in 1896 is only 45.7 ft. (see table p. 163), while that in 1895 is 



