SOCIETY OP NORTHERN ILLINOIS. 323 



gallons of water to the pound; or, if we follow Prof. Cook, 300 

 gallons for a second application. For the plum, 200 or 300 

 gallons of water to the pound of Paris Green; or, if London 

 Purple be used — a dangerous practice for this fruit — 160 to 200 

 gallons to the pound. For the cherry, 100 to 200 gallons of water 

 to the pound of London Purple, or 300 if applied the second 

 time. For the peach, London Purple should probably be dis- 

 carded, and Paris Green used at the rate of not more than a 

 pound to 300 gallons of water. 



(4) Reports do not precisely agree with regard to the number 

 of sprayings advisable, Cook spraying twice if heavy rains 

 require, but limiting himself to this number; Weed spraying 

 three or four times in his experiments; and Popenoe finding that 

 a second spraying produced but trifling additional effect. Clearly, 

 here, more experimentation will be required. 



(5) Elaborate, but still imperfect, experiments intended to test 

 the resisting power of the tree, scarcely do more than show 

 that great caution must be used in applying the arsenites, and 

 that several conditions, most of them undetermined, influence the 

 effect of the poison on the tree. Indeed, some experimenters 

 have reported that not only trees of the same variety and age 

 treated in precisely the same way, at the same time, may show 

 widely different amounts of injury, but that different sides of the 

 tree, and even different branches of the same side, sometimes 

 show similar differences. With regard to the principal kinds of 

 fruit trees, it is clear that the cherry is the hardiest of all in this 

 respect, and the peach the most sensitive, the plum being, 

 further, more easily injured than the apple. 



(6) We now know that the plum or peach curculio can be 

 killed by poisons not strong enough to do serious harm to the 

 tree, whether plum or peach, at least under favorable circum- 

 stances. Probably we ought not to go farther than this at the 

 present time. I think that the most important additions to our 

 knowledge on this subject are those which show the varieties of 

 food and the feeding habits of the adult curculio. 1 ought to add, 

 that even if poisons are found thoroughly destructive to the 

 insect, and safe for the tree, their application may nevertheless 

 be ineffective, on account of the number of repetitions which 

 would be required. A part of the curculios — how large a part 

 has not yet been ascertained — certainly pass the winter in the 

 earth as pupse, and appear long after the older members of their 

 brood have begun operations on the fruit ; it is quite possible, 

 consequently, that spraying must be kept up so long to protect 

 against these late comers as to make it too expensive for the crop, 

 or even to endanger poisoning the fruit when ripened. 



(7) Popenoe's experiments seem to show that, however effec- 

 tive for early apples, spraying with poisons will not alone 

 accomplish the purpose for late varieties, since it cannot be used 



