APPENDIX. ix 



tally with the results they obtained. They used one pound of 

 Paris green to one hundred and fifty gallons of water, and when 

 Mr. Sessions and I went over there in the summer we saw that the 

 trees were burned very little. The same proportions used at 

 Amherst burned the trees very badly. Yet Professor Cook and 

 others have reported that a much larger proportion of Paris green 

 could be used. The Paris green I used I had analyzed and know 

 just what it was. I expect there is either some great difference 

 between the climate of Amherst and this region — or something 

 else. 



Mr. Craig. So far as my own orchard is concerned, where the 

 Paris green was used a streak was burned here and there, in other 

 places not. I think it was not kept stirred up. 



Professor Fernald. Suppose it is not possible to destroy these 

 insects : even then I believe it would pay to make annual appro- 

 priations to hold them in check. We know what the farmers are 

 paying annually to destroy the potato beetle, and if this insect 

 spreads over the Commonwealth of Massachusetts I should sup- 

 pose it was capable of doing more damage than the potato beetle. 

 It seems to me, if it is not possible to stamp it out, it is wise to 

 hold it in check where it is. 



Mr. Sessions. I have heard the idea advanced by somebody 

 from Medford that possibly the reason the caterpillars apparently 

 eat Paris green and live is that after a certain stage of their 

 existence they stop eating altogether. 



Professor Fernald. They do not stop eating long before they 

 spin their cocoons. The time is not more than twenty-four hours. 



Professor Shaler. I should like to ask about the chances for 

 more satisfactory insecticides. I should like to ask if we may 

 reckon among the insecticides certain compound salts of calcium 

 which are very acrid, and whether a solution of them would be 

 efficacious ? 



Professor Fernald. I have had no experience with them. 



Professor Shaler. The question is, whether it would serve in 

 this case. Do you know. Professor Riley ? 



Professor Riley. I should have most faith in the arsenicals. 

 The relative value of the different forms of arsenic spraying depends 

 partly upon the kind of tree treated, partly upon the condition 

 of the atmosphere, and very materially upon the purity of the ma- 

 terial. Paris green has this advantage, that it may be used much 

 more strongly with less injury to the trees ; and it has this disad- 

 vantage, as compared with London purple or pure arsenic, that it 

 is not soluble in water, and you have to keep stirring it. I have 

 no doubt that the experience Professor Fernald refen-ed to was 



