504 Wisconsin Academy of Sciences, Arts, and Letters. 
It is obvious that the amount of any one species varies greatly 
at different times during its growing period. An effort was made 
to make collections within a short time from widely scattered 
stations, and to choose places where the plants were at or near 
maturity, so that results obtained from all stations would be com¬ 
parable and would indicate the average amount for the summer as 
a whole. Plants in shallow water usually reach maturity before 
Fig-. 1. Map of Lake Mendota showing stations and limits of the plant 
