SOME EXPERIMENTS WITH CONTACT INSECTICIDES. 523 



hyde alone, and no particular strength could be found which killed the 

 insects without injuring the plants. Sprayings of copper sulphate and 

 ferrous sulphate were also tried alone and combined with formalin, but 

 in no case could they be said to equal the old-established sprays in 

 efficacy. 



[Ampelopsis, Choisya, Euonymus, and Svlanum grew in the open; 

 the other plants in the plant-houses, the average temperature of which 

 was 620.] 



