441 



drying up of the lake. In September the lake did temporarily 

 dry up only to be re-entered by the October flood, in which an 

 unusual plankton (51.6 cm. 3 ) at once developed. 



• 1897. 

 ( PI. XI., XXIII., XXVI1L, XXXII., XXXIV., XXXVIII., XLI. ) 



This year is represented by 34 collections in the Illinois, 

 and 13 in Spoon River, and by 24, 6, 7, 18, and 9, in Quiver, 

 Dogfish, Flag, Thompson's, and Phelps lakes. It was a year of 

 protracted winter and spring flood, a late June rise, and pro- 

 longed low water in summer and autumn. The data of compar- 

 ative production are given in the accompanying table. 



PLANKTON PRODUCTION IN 1897.* 



Station 



Feb. 



March 



April 



May 



June 



July 



Illinois River 



Spoon River 



Quiver Lake 



Dogfish Lake , 



Flag Lake 



Thompson's Lake 

 Phelps Lake 



+1 



.04 



.047 

 .19 



•15 

 .07 

 .27 

 .19 



38 

 007 



34 

 48 

 83 

 65 

 44 



+ 



5. 11 

 .048 



13-38 

 8.18 

 8.55 



10.38 

 4.26 



+ 



5.62 

 .440 



1.29 



1.94 

 10.61 



7.88 

 22.58 



.27 



.250 



1 .26 



2.48 



4.87 



3-59 

 .42 



+ 



4.69 



7-13 

 3-3i 

 9.49 



Station 



Aug. 



Sept. 



Oct. .Nov. Dec. 



Mean of 

 monthly 

 averages 



Spoon River 



Dogfish Lake 



+ 



3-65 | + 

 .652 - 



8.83 



5-13 

 .16 



+ 



5-95 



+ 

 4- 



1 .00 



1. 671 



.09 



-, -5 6 

 +. -559 

 - .007 



+ 

 + 



+ 



3.28 

 1 .225 

 1. 71 

 2.65 



5-34 

 10.41 

 9.15 



.21 



- 



- 



.04 



Flag Lake 



















1 



Thompson's Lake . . . 



+ 



19.40 

 25.70 



+ 



10.01 



+ 



35-35 



+ 



16.67 



+ 6. 9 8 









1 





1 



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



The infrequency of collections in January-June and the 

 suspension of work in Dogfish, Flag, and Phelps lakes before the 

 year ended, render general comparisons with other years of less 

 value because of insufficient data. 



The annual channel production, 3.28 cm. 3 per m. 3 , — the mean 

 of monthly averages, — or 3.69, the average of all collections, is 

 21 or 68 per cent, respectively above the means, and 6 of the 11 



