162 KRAEMER— DILUTE SULPHURIC ACID [April 20 



hand atomizer was used for the spraying operation, and the plants 

 were usually sprayed late in the afternoon so as to avoid concentra- 

 tion of the solutions before they were absorbed, as also the burning 

 effects of the sun. It was found that a solution of i to 200 pro- 

 duced a marked burning effect on the leaves, and in the case of some 

 plants, as blackberry, polygonatum, oxalis, pear, rose, mulberry, 

 raspberry, etc., contiguous parts of the plant exhibited signs of 

 injury. 



It was soon found that there is considerable difference in the 

 resisting power of plants when sprayed in this manner. The most 

 sensitive plants were peach, raspberry and wild carrot, while the 

 most resistant were poison ivy and plantain (Plantago major). As 

 a result of these experiments it was found that most plants could be 

 sprayed with a solution of sulphuric acid varying in strength from 

 I part in 500 to i part in 1000, without serious injury to the plants, 

 and the conclusion was reached that it would be perfectly safe to use 

 sulphuric acid solution as a spray in the strength of i part of acid to 

 1000 parts of water. 



Later in the summer of 1904 it was my good fortune to find 

 a rose garden in which some of the plants were badly affected with 

 mildew and to obtain permission of the rose-grower to treat the 

 affected plants. In the series of experiments a solution having a 

 strength of i part of acid to 1000 parts of water was freely applied 

 by means of a garden syringe, so that the plants were thoroughly 

 wetted. Sprayings were made as follows: August 11 at 4 P. M., 

 August 12 at 8 A. M., August 13 at 8 A. M., August 14 at 8 A. M., 

 August 15 at 8 A. M., August 16 at 8 A. M. 



Within about a week afterward the mildew had about all disap- 

 peared and the young leaves which were putting forth showed no 

 signs of injury. During 1905 the mildew did not re-appear, and it 

 was noticed that the plants which had been sprayed with the sul- 

 phuric acid solution the year before had never done better. 



It may be of interest to state that parallel experiments using 

 copper sulphate, i to 1000, were conducted with the result that while 

 the mildew was eradicated the tips of the young leaves were injured. 



During the winter of 1904-05 I had an opportunity of trying 

 the solution on roses growing in the green-house. The plants were 



