312 TRANSACTIONS OF THE HORTICULTURAL 



sometimes as Paris Green. These substances are about the 

 equivalent of a mixture of two pounds of Paris Green to a 

 hundred pounds of plaster. 



COMPARATIVE ADVANTAGES OF ARSENICAL POISONS. 



It is now generally admitted that a solution of white arsenic 

 as so much more liable than London Purple or Paris Green to 

 injure the foliage, even of the apple (varying in the gravity of 

 the injury according to circumstances not yet well understood), 

 that it is no longer recommended for this purpose. Its only 

 advantages are cheapness and convenience of application, since 

 it does not require stirring, but the London Purple costs no 

 more. Mr. Gillette, of the Iowa Experiment Station, believes 

 from experiments made this summer, that white arsenic, if 

 stirred up in water and applied while fresh, before solution has 

 taken place, is much less liable to injure the leaves. 



It is commonly known that London Purple is more convenient 

 of application than Paris Green, on account of its greater fine- 

 ness and lightness, and it is also decidedly cheaper; but Cook 

 of the Michigan Station, and Gillette, of Iowa, are quite of the 

 opinion that it is more caustic to vegetation. Weed, of Ohio, 

 on the other hand, considers it less likely to scorch the tree, as 

 stated in his Bulletin No. 3, issued in May of last year; and 

 Popenoe, of Kansas, finds no great difference between the two. 

 My own experience has gone to show that Paris Green is prefer- 

 able in this respect. Doubtless, further careful experiments on 

 this point will be necessary, carried out with reference to vary- 

 ing conditions of tree, weather, season, and time of day. 



MIXTURES AND APPLICATION. 



These poisons, as is well known, may be applied either dry or 

 wet, the advantage of the latter mode being, according to Riley, 

 especially evident in dry weather. The poisons may be, also, 

 much more cheaply applied and quickly prepared with water 

 than with any dry diluent. Eiley advises adding two or three 

 pounds of starch to each barrel of the water mixture, (to pro- 

 mote its adhesion to the surface and to assist in the suspension 

 of the poison in the water)- He also thinks that sifted wood 

 ashes stirred in with the poison lessen its caustic action on the 

 leaves. 



Dry poisons are to be preferred in rainy weather especially, 

 because they may be applied without heavy apparatus which it 

 would be difficult to drag through the field when the ground was 

 soft. Dr. Riley also believes the dry arsenites much less liable 

 to injure the foliage. Flour, he finds the most satisfactory 

 diluent, having the advantage of adhesiveness, but being expen- 

 sive, it may profitably be mixed with one third wood ashes. 



