316 TRANSACTIONS OF THE HORTICULTURAL 



to determining at once the comparative effects of London Purple 

 and Paris Green mixtures of various strengths, and also the re- 

 sisting power of the various varieties of apple, he treated ki 

 May, 1888, no less than four hundred and sixty-eight trees, spray- 

 ing sometimes once and sometimes twice; his London Purple 

 mixtures being a pound to sixty-four gallons of water and one 

 pound to 128 gallons, and the Paris Green preparation varying 

 from fifty gallons to 320 gallons to a pound. Careful estimates 

 •of the foliage destroyed were made for each tree by the same ob- 

 server at the same time. From his tables I collect the follow- 

 ing general results : In the first place the Winesap was worse 

 affected of the eight varieties sufficiently tested, the loss aver- 

 aging twenty-eight per cent, of the leafage on twenty-four trees 

 of that variety. Tnen came the Gilpin, with twenty-two per 

 cent., the Talman with fifteen per cent., the Johnson with 

 twelve, the Yellow Bellflower eleven, the Huntsman ten, the 

 Wagener nine and the Janet eight. Eighteen trees treated with 

 the weakest London Purple mixture — a pound to 128 gallons — 

 averaged only a loss of twenty-five per cent. ; while twenty-seven 

 trees treated with a mixture of twice that strength lost eighteen 

 or nineteen per cent, of their leaves. The damage by Paris 

 Green varied from seven per cent., where a pound to 320 gallons 

 was used to twenty per cent, where a pound was used to eighty 

 gallons. A second spraying rarely increased the damage ma- 

 terially. As between Paris Green and London Purple the differ- 

 ence is scarcely discernible. 



By some of these experimenters it is believed that the injury is 

 due to the absorption by the tissue of the leaf of the dissolved 

 portion of the poison — an idea which would explain the greater 

 damage done when the application is followed by rain, unless, 

 indeed, the latter is copious enough to wash away the insecticide. 



Gillette experimented in 1888 especially with white arsenic, dis- 

 solving it by boiling and applying in strengths varying from one 

 pound to 200 gallons of water to one pound to 800. Notwith- 

 standing the apple leaves received a continued wash of rain, for 

 twenty-four hours three days after the application, the solution of 

 one pound to 250 gallons of water scorched at least one half of 

 the leaf surface and a fortnight later ninety per cent of the leaves 

 fell from the tree ; while one pound to 400 gallons scorched the 

 tips and edges of the leaves. In another experiment made this 

 year even one pound to 1200 gallons damaged nearly every leaf. 



Plum. Cook sprayed eighteen plum trees with London Pur- 

 ple with the following results: Six treated with one pound to 200 

 gallons of water were uninjured after ten days; five sprayed with 

 a pound to a hundred gallons were somewhat hurt ; three others 

 much hurt ; and three more — the spraying followed next day by 

 rain — were very badly damaged, as was also a single tree 

 sprayed July 10 with only one pound to 200 gallons. Weed 



