245 



(liately washed off with water, and in this case the injury to the foliage 

 was sligiit. 



When the filtered soluble portion of London purple was used the 

 foliage was much injured, but when the filtered solution from which 

 the arsenite had been removed was sprayed upon the tree no injury re- 

 sulted, showing that it is the arsenic and not the dye which is injurious. 



Loaves injured bj' Loudon purple applied iu the proportion of 1 pouud to 250 gal- 

 lons of water were found, after thorough washing, to contain arsenic in the texture 

 of the leaf (0.00213 gram of arsenic iu 58 grams of leaves). Tsvo analyses of leaves 

 iujured by Paris green in the same lot showed no arsenic in the texture of the leaf. 

 The poison in the latter case had acted upon the surface of the leaf. Id is apparent 

 that London purple is the more injurious because of its soluble arsenic. The arsenic 

 iu Loudon purple is iu the form of a normal arsenite of calcium, which substance 

 comprises about 72 per cent of the whole compound, and over .50 per cent of it, or 

 nearly 40 per cent of the London purple, is quickly soluble iu water. Paris green 

 contains no soluble arsenic. 



Experiments with coarse and fine sprays for applying the arsenites 

 indicated that the former method is likely to do more injury to the 

 foliage. 



Our trials were made at nearly all times of day and under various meteorological 

 conditions. Full records were made of all these conditions ; but as they appear to 

 have exercised no influence whatever, they need not be discussed here. The notion 

 that foliage may be scorched by spraying with pure water on a bright and hot day 

 has no foundation, else our trees would have been scorched by the Paris-green 

 water, which was sometimes applied iu very hot and bright weather. 



In two experiments with Loudon purple applied to plum-trees, no injury was done, 

 though a careless observer would have said that the plums were injured, as many of 

 the leaves were spotted and often perforated. But these injuries were entirely fun- 

 gous (in this case, apparently due to Phyllosticta jyyrina) and were easily distin- 

 guished from j)oison injuries. 



Conclusions. 



(1) Peach trees are very susceptible to injury from arsenical sprays. 



(2) London purple is much more harmful to peach trees than Paris green, and it 

 should never be used upon them in any manner. 



(3) Injury is more liable to occur upon full-grown foliage and hardened shoots than 

 upon young foliage and soft shoots. 



(4) The immunity of the young growth is due to its waxy covering. 



(5) Injury late iu the season is more apparent than early in the season, because of 

 the cessation of growth 



(6) Injury from the use of London purple may be permanent and irreparable. 



(7) The length of time which the x>ois(jn has been mixed appears to exercise uo in- 

 fluence. 



(8) London purple contains much soluble arsenic (in our samples nearly 40 per 

 cent), and this arsenic is the cause of the injury to peach foliage. 



(9) A coarse spray appears to be more injurious than a fine one. 



(10) A rain following the application does not appear to augment the injury. 



(11) Meteorological conditions do not appear to influence results. 



(12) Spraying the peach with water on a bright and hot day does not scorch the 

 foliage. 



(13) Paris green, in a fine spray, at the rate of 1 pound to 300 gallons of water, did 

 not injure the trees. Probably 1 pound to 350 gallons is always safe. 



(14) We do not discourage the general use of London purple, as we use it freely 

 upon other plants than the peach. 



