TWENTY-FOURTH ANNUAL FRUIT-GROWERS' CONVENTION. 93 



may be no blackening of the leaf observed at any time, but the leaf may 

 become prematurely yellow and drop off within two or three weeks from 

 the time the application was made; showing that the poison which 

 entered the plant, though not enough to kill it at once, deranged its 

 functions to such an extent as to cause this premature dropping. 

 These two forms of poisoning we have designated as the acute and the 

 chronic poisoning of arsenic. 



The amount of poisoning that may occur, other things being equal, 

 seems to be entirely dependent upon the amount of soluble arsenic in 

 the spraying mixture, though there are conditions of the plant when it 

 is possible to spray even with a solution of arsenic and produce no evil 

 effects. We know that under certain conditions leaves will absorb 

 water, and under other conditions not at all; so it may be supposed 

 in cases where solutions of arsenic have been applied without injury, 

 that the plant was in such a condition that no absorption of water took 

 place and none of the arsenic solution entered the plant; and that 

 before the leaves became again absorbent the water had evaporated, 

 leaving the arsenic upon the leaves in a dry form. This might flake 

 off and blow away from the leaves before they are exposed to a dew or 

 fog. It may be that when we know more about the effect of weather 

 upon the leaves, we will be able to spray at times when the leaf is least 

 susceptible to injury, and so lessen the danger to the plant. 



Prevention of Injury. — A chemical means of avoiding the injury of 

 Paris green has been used considerably. It consists in adding a large 

 amount of lime to the water in which the Paris green is mixed, and this 

 appears to be. sufficient to render insoluble any slight amount of free 

 arsenic or other soluble arsenites that may be present. The use of lime 

 with Paris green has now come to be recognized as a very important 

 precautionary measure in preparing this spraying material, chiefly 

 because of the presence of white arsenic in the Paris green that has 

 - been manufactured of late years. The amount commonly recommended 

 varies from one to ten parts of lime to each part of Paris green. If the 

 amount of free arsenic in the sample is not too high, good effects will 

 result from adding the lime; but beyond a certain point the lime does 

 no good, and may even do harm. It has long been known that lime 

 acts on white arsenic, when the latter is in suspension in water, in such 

 a way as to render it much more injurious to foliage than the arsenic 

 would have been without the lime. 



Laws Concerning Paris Green. — A number of the States, including 

 New York, Louisiana, Texas, and Oregon, have enacted laws requiring 

 the Paris green sold on the market in those States to contain fifty per 

 cent of arsenious oxid. These laws differ somewhat in detail in the differ- 

 ent States, but agree in establishing this standard for purity. Appar- 



