86 



season. A second tree, sprayed in the beginning, was abandoned 

 because the orchard in which it was situated was pastured with 

 cattle. 



The London purple used was obtained from the Hemmingway 

 London Purple Company, New York, with the understanding that 

 it was intended for experiment and under a promise to report the 

 results to them. There is consequently every reason to suppose 

 that it was a good sample of the article. By Prof. McMurtrie it 

 was found to contain 2*2.25 per cent, of metallic arsenic. Compar- 

 ing this ratio with that given for the Paris green we find that in 

 applications of the latter substance we used the equivalent of 50.5 

 grains of metallic arsenic to the bucket of water (-20 grains to the 

 gallon) and in the London purple applications 37.2 grains of ar- 

 senic to the same (nearly 15 grains to the gallon), — the Paris green 

 fluids being thus about one third stronger in arsenic than the Lon- 

 don purple. In Paris green the arsenic is combined with copper 

 to form an arseniate of copper, while in London purple it is com- 

 bined with lime to form the arseniate of lime. Whether this differ- 

 ence in composition is likely to make any perceptible difference in 

 the insecticide activity of the two substances, I am unable to say. 



The tree was treated eight times, as in the Paris green experi- 

 ment, commencing June 13 and ending September 3, and, as usual, 

 a check was selected in its immediate vicinity, not treated at all. 

 The course of events was in all respects similar to that detailed 

 under "Paris Green," except that the differences between the pois- 

 oned tree and its check were, all along, less than in the other ex- 

 periment. For example, 31 per cent, of the fallen apples obtained 

 July 16 from the poisoned tree had been injured by the codling 

 moth as against 52 per cent, from the check, while the correspond- 

 ing Paris green trees gave us at this date, it will be remembered, 

 7 per cent, and 53 per cent. 



Examining the whole number of fallen apples collected during 

 the season, we found that of 1,048 from the experimental tree, 

 495, or 47 per cent., had been penetrated by the larva of the cod- 

 ling moth, while of the 1,828 apples gathered under the compan- 

 ion check, 1,040, or 57 per cent., were so injured. Of these fallen 

 apples, consequently, the number injured in the check lot was only 

 about 10 per cent, greater than those injured in the experimental 

 collection. The picked apples at the end of the season gave a sim- 

 ilar result, 61 per cent, of those on the experimental tree having 

 been injured by the codling moth and 76 per cent, of those on the 

 check, — a difference, in this case, of only 15 per cent, in favor of 

 the poisoned tree. 



Taking all the apples, both fallen and ripened, we find that 49 

 per cent of those treated with London purple were injured and 59 

 per cent, of those not so treated ; again a difference of only 10 

 per cent, in favor of the experimental lot. Comparing the general 

 averages of these London purple trees with those of the trees 

 sprayed with Paris green, we see that the latter application was 

 from two to three times as elYeetive as the former — both being 

 used in quantity to burn the foliage. 



