SOCIETY OF NORTHERN ILLINOIS. 313 



Road dust is a poor substitute. Various other adhesive sub- 

 stances may be used advantageously, especially in wet weather, 

 dextrine, gum-arabic, slippery-elm bark, or rosin, about two 

 pounds of either to twenty-live of the poison mixture being a 

 good average. 



Gillette reports experiments intended to test the difference in 

 effect of a fine or coarse poison spray. He finds little difference, 

 so far as injury to the foliage is concerned, between a fine spray 

 distributed with a Nixon nozzle and a solid stream thrown with 

 force, provided that in both cases the leaves be equally moisten- 

 ed. Doubtless a slight moistening can be more equably dis- 

 tributed as a fine spray than in coarse drops. 



STRENGTHS OF MIXTURES. 



Riley finds the proportions of Paris Green to the dry diluent, 

 whatever that may be, to vary from one in twenty to one in thirty- 

 five, and recommends about one in thirty as efficient. Of Lon- 

 don Purple he advises the use of about one pound in forty-five, 

 the diluents being fifteen pounds of wood ashes and thirty of 

 Hour, with a little less than two pounds of some adhesive 

 substance. 



Cook uses for the apple, cherry and pear one pound of Lon- 

 don Purple to 200 gallons of water, but finds this too strong for 

 the peach. If the application is repeated, he would then use one 

 pound to 300 gallons. For plums he does not now use London 

 Purple at all, but would apply Paris Green, one pound to two or 

 300 gallons of water. For the peach, only Paris Green is appli- 

 cable, and this in strength no greater than one pound to 300 gal- 

 lons of water. 



Gillette, of Iowa, recommends for dry application one pound 

 of the arsenical poisons to fifteen of land plaster or plaster of 

 Paris. His wet mixture advised in 1888 was one pound of Lon- 

 don Purple to 100 gallons of water as a maximum for apples, 

 and one to 160 as a minimum. Of Paris Green he would use 

 for apples one pound to 120 gallons as a maximum, and one 

 to 180 as the minimum, but in 1889 he reduces this minimum to 

 one to 160. For the plum he recommends Paris Green in pro- 

 portions varying from one pound to 160 gallons of water, to one 

 pound to 200 gallons. If weaker than the latter ratio he believes 

 that heavy dews or light rains would compel repetition. 



In his cherry experiments for the destruction of the curculio, 

 Weed, of Ohio, in 1888, used one pound of London Purple to 

 100 gallons of water; and for the apple one pound of London 

 Purple to 100 as a minimum, and to 130 as a maximum, Paris 

 Green one pound to 100 gallons. In 1889, he found one pound 

 of London Purple to 160 gallons of water effective for the 

 cherry. 



