535 
May 12,1923 Injury to Foliage by Arsenical Spray Mixtures 
(8) The injury to leaves is characterized, first, by a lack of luster, 
then wilting, and a final change to some shade of brown (dependent 
upon the species of plant) as the affected tissue becomes dead and brittle. 
The symptoms are not sufiiciently distinctive to separate arsenical injury 
from some others. 
(9) The injury to the foliage is practically all through the lower 
epidermis, regardless of the numbers of stomata in the two surfaces, 
indicating that it is a result of direct penetration of the thinner cuticle. 
(10) Individual plants of the same species and variety vary somewhat 
in their susceptibility to arsenical injury. 
(i i) The older leaves of a plant are more susceptible than the younger 
ones. 
(12) Soap added to soluble arsenicals offers a slight protective action. 
(13) Soap added to most insoluble arsenicals increases the injury by 
increasing the solubility to a point more than counteracting its slight 
protective action. 
(14) Soap added to Paris green in suspension distinctly restrains the 
burning of foliage. 
(15) Gelatin, milk, and agar do not increase the arsenical injury to 
foliage. 
(16) Lime sulphur increases the injury caused by most insoluble 
arsenical compounds. 
(17) Lime sulphur distinctly decreases the injury caused by calcium 
arsenite but not to a sufficient extent to make this a safe insecticide. 
(18) Tobacco extract has little influence upon the injurious properties 
oi arsenical insecticides. 
(19) Lime restrains, to some extent, the injury by calcium arsenite 
and Paris green. 
(20) We have not been able to decrease the zinc arsenite injury by 
adding ferrous sulphid. 
(21) Repeated spraying with zinc arsenite is liable to result in serious 
burning. 
(22) A slightly wilted condition of the foliage does not result in in¬ 
creased injury. 
(23) Light seems not to be an important factor in arsenical injury to 
foliage. 
(24) An increase in atmospheric temperature results in a moderate 
increase in arsenical injury; but within the ranges of temperature found 
during the summer in a suitable orchard climate this is of little practical 
importance if the air is relatively dry. 
(25) Humidity is the greatest environmental factor in determining 
arsenical injury to foliage, and this influence is very marked even before 
the saturation point is reached. 
(26) Using a few experiments as a basis for generalization upon 
arsenical injury is a treacherous proceeding and may lead to erroneous 
conclusions. The only safe procedure is to test repeatedly each point 
under consideration. 
literature cited 
(1) Bourcart, E. 
1913. INSECTiaD^S, PUNGICID]eS, AND WEEDKn.I.ERS. XXXV, 431 p., iUuS. 
London. 
(2) Cunton, G. P., and Britton, W. E. 
1912. TESTS OR SUMMER SPRAVs ON APPLES, PEACHES, ETC. In Conn. Agf. Exp. 
Sta. 35tli Ann. Rpt. 1911, p. 347-406, pi. 17-24. 
