525 



COMPARISON OF MONTHLY MEANS OF PLANKTON PRODUCTION IN ILLINOIS 

 AND SPOON RIVERS, BASED ON ALL CATCHES.* 





January 



February 



March 



April 



May 



June 



Year 



« 



pi 



a 

 

 

 a 



CO 



Ctf 



pi 



a 

 

 



a 



00 



pi 



Pi 



a 

 







pi 



pi 



e 

 

 

 a. 



CO 



pi 



pi 

 a 



3 







Q. 



00 



pi 



pi 



c 

 

 



D, 

 C/2 



1894 

 1895 

 1896 

 1897 

 1898 

 1899 























0.74 

 30.42 

 0.72 

 0.27 

 3-96 









O.OI 

 0.02 

 0.04 









3.18 

 5.67 

 5. 11 



4.40 











O.OI 





0.017 



0.07 

 0.38 



007 



0.048 



1 .30 



5.62 



11.30 



0.440 

 0.023 



O.250 

 O.O96 



0.45 

 0.18 



O.OI7 

 O.OO5 



O.27J0.OI6 



0.810. 001 



0.330.124 

 0.28 0.026 















Monthly a v. 



0.213 



O.OII 



0.23 



0.021 



0.27 



0.052 



4-59 



0.048 



6.08 



0.232 



7.22 



O.I73 





July 



August 



September 



October 



November 



December 



Year 





pi 





Pi 





pi 





pi 





pi 





pi 





« 



a 



Pi 



a 



P4 



c 



« 



c 



~> 



a 



pi 



a 





• 







■ 













; 







■ 







t ; 

















































in 





a. 

 co 





C/3 





C/3 





a. 



C/2 





a. 



CO 



1894 



5.12 





9.67 





1.36 





0.6l 





0.10 





O.IO 





1895 



9-33 





4-°3 





1.52 





0.57 





3.02 





1. 14 





1896 



1.44 





1 . 12 



0.018 



0.38 



0.005 



I. II 



0.005 



0.02 



0.005 



0.76 



0.002 



1897 



4.69 





3-65 



0.652 



8.83 



5-130 



5-95 





1 .00 



1 .671 



0.56 



0.599 



1898 



0.58 



0.036 



0.91 



0.002 



0.69 



0.002 



0.24 



0.001 



0.25 



O.OOI 



o-99 



0.001 



1899 





















































Monthly av. 



4-23 



0.036 



3-88 



0.224 



2.56 



I. 712 



1.70 



0.003 



0.88 



0.559 



0.71 



0.201 



*Amounts in this table are cubic centimeters of plankton per cubic meter of 

 water after subtracting from the total catch the estimated amount of silt. 



meters. This is 4.7 times as much as the average of all the 

 Spoon River collections — 11.5 times, if we omit the two 

 exceptional collections of September 11 and 30, 1897, and 44 

 times, if we exclude the low-water period of the autumn of 

 1897 from both averages. This latter ratio, 1 to 44, represents 

 the relative plankton content of the two streams except during 

 periods of prolonged and extreme low water. Even in such 

 low-water periods the waters of the tributary are less pro- 

 ductive than those of the main stream. For example, the aver- 

 ages of the monthly averages of production for July-October, 

 inclusive, in the two streams are respectively 2.89 and 5.78 cm. 3 



