31 



and cotton. The fruit trees in this series and the cotton plants were all 

 young and vigorous. The weather conditions subsequent to the appli- 

 cations were favorable, as in previous experiments, no rain falling for 

 a sufficient time to give a very satisfactory test. As before, all poisons 

 applied were freshly mixed, and in every case lime was added equal in 

 weight to the poisons used. The poisons were Paris green, ordinary; 

 Paris green, pulverized ; London purple, and Scheele's green. The first 

 test was at the rate of 1 pound to 200 gallons of water. No signs of 

 injury developed after two weeks, even on the tender foliage of peach 

 and cherry. The applications were renewed on the same plants at the 

 rate of 1 pound to 100 gallons of water. For a week no injury was 

 apparent, even at this unusual strength, but after that period the 

 leaves began to fall from the peach trees treated. The falling leaves 

 were green and unspotted or scalded, but their connection with the 

 stems was much weakened and the least wind caused them to fall to 

 the ground. This falling continued for several days, in most cases 

 resulting in the loss of nearly all the foliage. A few of the remaining 

 leaves afterwards became somewhat scalded. In the case of the apple 

 a scald in brown spots resulted in varying degree with the different 

 washes, and in the cherry the injury was very slight and insignificant. 

 No damage whatever resulted to the cotton. 



The following table indicates the amount of damage caused by the 

 different poisons : 



Poison. 



Peach. 



Apple. 



Cherry . 



Cotton. 



Paris green, ordinary.. 



Paris green, pulverized . 



Scheele's green 



London purple 



£ leaves lost... 

 | leaves lost... 



Very slight spot- 

 ting. 



All more or less 

 spotted, 

 do . 



No in jury 



Injury slight — 

 insignificant. 



No injury whatever. 

 Do. 

 Do. 



All leaves lost. 



Much scalded, in- 

 cluding edges. 



do 



Do. 







This application was made at this unusual strength, especially to 

 peach, with the intention of causing injury, so as to be able to deter- 

 mine the relative amounts. The injury resulting from the Scheele's 

 green was not very much greater, if any, than with the Paris green 

 pulverized, and probably resulted from the more finely divided condi- 

 tion of the powder, as a corresponding increase of damage is seen 

 between the ordinary Paris green and the same pulverized. The damage 

 by London purple in the case of peach and apple was much greater 

 than with the other poisons. 



It may be noted here that the effect of an arsenical spray on the plant 

 is often long in being manifested. This has been previously noted in 

 the course of experiments with these poisons conducted by the Division 

 of Entomology in different years, and was again shown the present sea- 

 son in the work against the elm leaf-beetle. Trees on the grounds of 

 the United States Department of Agriculture were sprayed repeatedly, 



