LONDON' PURPLE : METHODS OF USING. 35 



Its effects are more permanent, as from its fine state of pulveriza- 

 tion it is partially absorbed by the leaves. 



Tlie color that it imparts to vegetation shows its application and 

 may serve to prevent tlie careless use of poisoned plants for food. 



In its condition of a very fine powder it admits of a more thorough 

 admixture when used dry, and is more easily kept in suspension in 

 water. 



Method of using. — It may be mixed witli flour, plaster, or any of 

 the diluents mentioned for Paris green, and dusted upon the vegeta- 

 tion by any of the means there given which may be found the most 

 convenient. When prepared of the strength of one pound of the pur- 

 ple to ten of flour it will injure only delicate vegetation. Reduced 

 with seventy pounds of flour, it will be found to kill nearly all of the 

 leaf-eating larva. For general use, the proportion recommended, and 

 which has given the best practical results, is one pound of the purple 

 to forty of flour or other substance. 



Its application in water may also be made as directed for Paris 

 green. With one pound mixed with forty gallons of water, some vege- 

 tation has been injured. A dilution with forty gallons of water will 

 probably destroy most larvse. For quite young and more delicate ones, 

 a dilution of one iiundred gallons will suffice, and the experiments of 

 the Entomological Commission in the cotton fields have shown that 

 in dry weather and under other favorable conditions, with a pound of 

 the purple mixed in one hundred and fifty gallons, the cotton-worm 

 was readily killed. It should be mentioned that the cotton-worm — 

 Aletia argillacea, Hiibn., has been found to be more sensitive to the 

 poison than some other larvas of the Noctuidm. It is, of course, desir- 

 able that the poison be not used in greater strength than is needed for 

 killing the species to be destroyed, and the maximum degree of dilu- 

 tion can easily be ascertained by experiment. 



The addition of a small quantity of flour to the water will give 

 greater adhesiveness to the poison. 



Useful in the destruction of the Apple-worm. — London purple 

 has been used successfully by Prof. A. J. Cook for destroying the apple- 

 worm or codling-moth — Carpocaina pomonella (Linn.). In his re- 

 cent experiments, continued through two seasons, a tablespoonful was 

 mixed with a pail of water, and this quantity was sufficient, usually, for 

 three trees. It was used in early summer, and the results were very 

 satisfactory, as a large proportion of the fruit was saved from attack. 

 It was believed that the purple formed a thin coating over the fruit 

 and prevented the deposit of the eggs (the eggs are deposited soon after 

 the apple forms), or that the upturned calyces at this time held suffi- 

 cient of the poison to kill the newly-hatched larvae in the attempt to 



