430 



1894. 



(PI. VIII., XXV., XXXV. ) 



Only three stations were established in this year : the Illi- 

 nois River Station, with 10 collections ; Quiver Lake, with 14 ; 

 and Thompson's Lake, with 5. The appended table gives the 

 production in monthly averages of plankton per m.-^ for the 

 seasons covered by the collections. 



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



It is evident from comparisons with records in years of fre- 

 quent collections, for example, in 1898, that the interval of col- 

 lection is too great in 1894 to give a satisfactory basis for a dis- 

 cussion of production. As far as they go the data indicate a 

 level of production below the average of our records. In the 

 river and in Quiver and Thompson's lakes the monthly aver- 

 ages in 1894 are below the general averages for the respective 

 months in 5 out of 7, 4 out of 7, and 2 out of 5 months respec- 

 tively, a total of 11 out of 19. The mean of the monthly aver- 

 ages in 1894 for the river, 2.53 cm.' per m.\ is 7 per cent, below 

 the mean of all monthly averages in 1894-1899, and that of 

 Quiver Lake is 49 per cent, below its mean. Thompson's Lake, 

 on the other hand, with 8.89 cm.^ presents an excess of 8 per 

 cent. 



The low level of production in the river and Quiver Lake 

 is attributable to the absence of overflow in June with its ac- 

 companiment of run-off of impounded and plankton-rich wa- 

 ters, to flushing action of the repeated rises in September, and 

 to the relative dominance of coarse vegetation in the lake and, 

 to some extent, in the river. The larger production in Thomp- 

 son's Lake is attributable to freedom from the flushing action 

 of floods in the prevalent low water and to the relatively stable 



