444 



September. Quiver Lake, however (PI. XXVIII.), pursues a 

 different course, production there dropping^ to a level rarely 

 exceeding .5 cm.'' for the remainder of the year. This results 

 from the greater relative volume of spring and creek water in 

 this lake. The discharge from Quiver Creek and the marginal 

 springs continued with relatively much less diminution through 

 the autumnal drouth than that from Spoon River, with the 

 result of making this lake far less productive of plankton at 

 this season than Spoon River (cf. PI. XXIII. and XXVIII.). 



1898. 



( PL Xn., XXIV., XXLX., XXXIV., XXXIX., XLII. ) 



This year is represented by 52 collections in the Illinois 

 and 11 in Spoon River, and by 26, 6, 25, and 22 respectively in 

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

 normally located and fully developed spring floods, followed 

 by low water in summer much disturbed by minor floods, with 

 a subsequent autumnal rise of unusual proportions. This re- 

 sulted in the highest average river levels in our years of opera- 

 tion, 8.02 ft. — a level almost equaling bank height. 



The accompanying table gives the data of comparative 

 production of the different localities in this year. 



PLANKTON PRODUCTION IN 1898.* 



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



