199 



the applications on single leaves. The arsenites were applied in three 

 ways, viz., (1) by jarring from a stiff brush, (2) by painting on the leaf 

 with a soft brush, and (3) by dipping the leaf in the mixture. The 

 problems studied were : (1) the relative amount of injury to the plant 

 by different arsenites ; (i.') the relation between the strength of the poison 

 and the amount of the injury; (3) the difference in the action of the 

 poisons on different plants ; (4) the amount of variation in the action 

 of the poisons on different varieties of the same plant; (5) the effect 

 of the age of the leaf on the amount of injury; (G) the difference in the 

 susceptibility of the different sides of the leaf to the effects of the poisons ; 

 and (7) the relation of the earlier to the ultimate effects of the poisons. 

 The details are reported in tables. 



(1) Amount of injury. — Paris green, London purple, and fresh and old 

 mixtures of white arsenic were applied to 1,180 leaves of the apple, 



'peach, sassafras, cotton-wood, and grape, causing 22, 56, 4, and 58 per 

 cents of injury respectively. The noticeable thing here is the small 

 amount of injury caused by the fresh mixture of white arsenic. 



(2) Relation of strength of poison to injury. — The three arsenic com- 

 pounds were applied to 828 leaves of the above-mentioned plants for 

 the most part in the proportions of one part of the poison to 100, 200, 

 and 400 parts of water. The amounts of injury by Paris green decreased 

 quite uniformly with the decrease in the strength of the mixture, but 

 the effects of Loudon purple and particularly of white arsenic were not 

 uniform. 



(3) Different effects of the poisons on different kinds of plants. — In the 

 case of applications of the three arsenic compounds to 240 leaves each 

 of the apple, peach, and grape, the per cents of injury to the respect- 

 ive kinds of plants were estimated at 39, 25, and 51, the relative 

 amounts of injury by the different arsenites remaining the same as in 

 the first experiment. A secondary effect, not apparent until after a 

 week or more, was observed on the older peach leaves. If this were 

 taken into account the injury to the peach would be increased 10 per 

 cent. 



(4) Variation in the injury to different varieties of the same kind of 

 2)lants. — Eight leaves of each of forty-four varieties of grapes were 

 treated with Paris green, London purple, and fresh and old white 

 arsenic. The estimated per cents of injury varied from 15 for the 

 Thomas variety' to 75 for the Wilder. 



(5) Effect of the age of the leaf on amount of injury. — Seven hundred 

 and seventy-four leaves, equally divided between old and young, of 

 the apple, grape, sassafras, and peach, were treated with the three 

 arsenic compounds. The old leaves suffered more than the young ones, 

 except in the case of the grape where the per cents of injury were 

 equal. In a general way this confirms previous observations by Pro- 

 fessors Cook and Bailev. 



