Huff: RESPONSE OF MICRO-ORGANISMS TO COri'ER SULPHATE 413 



suit in the complete destruction of Synedra. Whether this was 

 due to certain hardy individuals that were able to withstand a 

 treatment of that strength, or to the fact that the copper sulphate 

 was not distributed with absolute uniformity and that some on this 

 account escaped the treatment, we can not say. With these or- 

 ganisms pouring into the lake, however, in great quantities, as they 

 were here through the waters of the inlet, it is doubtful if a treat- 

 ment of several times this strength would have been effective for 

 more than five or six weeks. 



Among other organisms responding to a lighter treatment than 

 that suggested by Moore and Kellerman, may be mentioned Eudo- 

 rina and Pandorina, for which the above authors recommend the 

 use of one part of copper sulphate to 100,000 parts of water, and 

 Stephanodiscus, for which they recommend one part of copper sul- 

 phate to 250,000 parts of water. Eiidorina, having 100 standard 

 units per cubic centimeter of water, practically disappeared within 

 five days after above treatment. Pandorina, with 162 standard 

 units per cubic centimeter of water, dropped in eight days to an 

 occasional single individual in a sample, and it was more than a 

 month before either of these two organisms began to show any ma- 

 terial increase in numbers. Stephanodiscus, which for nearly three 

 weeks had maintained an average of 140 standard units per cubic 

 centimeter of water, almost completely disappeared within a week 

 after the second treatment, and only an occasional individual was 

 found for several weeks following. Late in August a slight in- 

 crease was noticed ; but the third copper treatment was given about 

 this time, and that put a check upon its development, and for more 

 than another month it was unable to establish itself again. As 

 samples were taken at several points in the lake, also from different 

 depths in the deepest part of the lake, both before and after the 

 treatment, and compared with samples taken daily at the weir, it 

 was found that these figures may be considered not as represent- 

 ing the varying conditions of small local areas, but as essentially 

 true for the entire lake surface, as well as for all depths down to 

 twenty feet or more below the surface. Below a depth of twenty 

 or twenty-five feet these and other algae were comparatively rare 

 all summer. 



About the twentieth of August, or more than a month after the 



