482 



yields least plankton. The factors of vegetation of the coarser 

 sort and of tributary waters serve here to modify and overbal- 

 ance light as a controlling factor in production. 



From the data of the U. S. Weather Bureau at Springfield, 

 Mr. W. G. Burns, Section Director, has kindly furnished me the 

 records of the number of cloudy days per month in 1894-1899 

 observed at Peoria, Havana, and Springfield. These are given 

 in the accompanying table. The records for Havana have also 

 been plotted on Plates VIII.-XIII. in the uppermost row of 

 squares. 



The variations in the relative cloudiness in the three local- 

 ities in many months and in the total number of cloudy days 

 in the several years in the three localities render any correla- 

 tion with production largely conjectural and close comparisons 



