174 PLUM. 



The following notes of some of the results of the series of 

 experiments undertaken officially by Dr. William M'Murtrie, 

 as Chemist of the United States Department of Agriculture, 

 in order to ascertain the effects of Paris-green on soil and 

 the plants grown therein, are of importance relatively to 

 occasional unfounded objections still urged against the use of 

 Paris-green : — 



" 1. An aggregate of 90G'4 pounds of Paris-green per acre 

 must be ap[)lied before any injurious effects on plant-growth 

 are appreciable. (The ordinary application to a Potato field 

 is from a pound to two pounds per acre.) 



*' 2. Arsenic cannot be absorbed and assimilated by the 

 plant in the economy of growth. All of the plants grown in 

 the arsenical soil tried by Marsh's test failed to indicate the 

 presence of arsenic. 



" 3. Potatoes subjected to applications of Paris-green failed 

 to give evidence of the presence of arsenic." * 



The above is useful as showing the safety with which Paris- 

 green may be used relatively to any fear of it being absorbed 

 by the roots into the tissues of plants grown in soil where this 

 arsenite may be present. On the surface of fruit or leafage 

 used for food, as, for instance, if it is used as a dressing for 

 Gooseberrj' caterpillar or on Cabbage leaves, it would obviously 

 he poisonous if partaken of. Therefore no article of food 

 dressed with Paris-green should be partaken of until either by 

 lapse of time, growth of the fruit, or careful washing, the 

 poison has been quite certainly removed. 



The cost of the Paris-green is very little. The firm with 

 whom I have chiefly corresponded on the subject inform me 

 that as wholesale manufacturers they could furnish quantities 

 of 1 cwt. and over at the rate of lOd. per lb. Retail dealers 

 would probably not furnish the pure article under Is. 3d. 

 per lb. 



London -2nir pie. — This preparation is an arsenite of lime 

 and has long been used as an insecticide in America, and foi 

 some years has been applied also in this country in the same 

 manner as the above-mentioned arsenite of copper, commonly 

 known as Paris-green ; but it is stated that, owing to its 

 lightness, a far smaller quantity by weight of London-purple 

 will treat a given number of trees than would be required 

 in the case of Paris-green. 



Very few observations have been sent to me from orchard- 

 growers regarding the use of this insecticide, but some good 

 notes on the subject, and as to its serviceableness for de- 

 struction of leafage caterpillars, have been communicated by 



* " Paris-green as an Insecticide," pp. 25-34, of Dr. Lintner's ' First Annual 

 lleport as State Entomologist of New York State, U.S.A.' 



