416 



MINNESOTA BOTANICAL STUD IMS 



conditions are favorable, and with the abundant nourishment now 

 present, they multiply with great rapidity. This perhaps accounts 

 for the high point reached by some of the organisms, especially 

 Stephanodiscus, late in the season while this autumnal shifting of 

 waters was going on. 



I 



j*^!: October November Decj 



:o :5o >o lo 3o . 9 19 Z7: 





I'ig. 1. General effects of copjjer sulphate upon the micro-organisms of Vadnais Lake. 



A brief study of the accompanying charts or figures will give a 

 much clearer idea of the effect of copper sulphate upon the various 

 organisms than can be given perhaps in any other way. The varia- 

 tion in the total of all organisms from June 11 to December 11, is 

 shown in figure 1. This chart shows also the variation of the two 

 diatoms, Synedra pulchella and Stephanodiscus niagarae, the two 

 most abundant organisms, as well as the changes in water tempera- 

 ture for the same period. On June 14, the day of the first treat- 

 ment with copper sulphate, the total number of organisms per cubic 

 centimeter of water was 8,100 standard units. Of these, 3,420 stan- 



