EXPERIMENT STATION BULLETINS, 373 



RESULTS IN 1893. 



In the experiments with tree-fruits this year the Bordeaux mixture of 

 2 lbs copper salt and 2 Bbs lime to 32 gallons of water was used for spray- 

 ing the fruits on the tree. The London purple was omitted. 



Pears were sprayed May 15, June 12, and July 10. One pound of the 

 fruit gave the equivalent of .100 grains of copper salt. 



Russian cherries were sprayed with Bordeaux mixture May 14, June 10 

 and 18, and on July 15 with modified eau celeste. 



One pound of fruit contained .147 grains of copper salt. 



Plums treated in the same way as Russian cherries, and at the same 

 time, gave .2 grain of copper salt to a pound of fruit. 



In these experiments, extending through two years, the minerals used in 

 spraying the fruits were found in appreciable quantities in every instance, 

 though the amount was small in all cases except when the spraying had 

 been purposely excessive. 



The inquiry naturally arises whether these poisons merely adhere to the 

 surface or penetrate the substance of the fruit? The results with goose- 

 berries seem to show that they penetrate the body of the fruit to a limited 

 extent. A test of this question has been made with some of the sprayed 

 pears. A pound of the pears was selected, the skin carefully pared off and 

 burned by itself, and the body of the pear burned to ashes by itself and 

 each ash separately analyzed. The pear pealings from 1 pound of pears 

 gave .106 grains of copper salt, and ^e flesh gave .071 grains, showing that 

 while most of the copper salt adheres to the surface, a portion finds way 

 into the body of the fruits. 



The copper salts adhere to vegetable surfaces more persistently than is 

 commonly supposed. A student in chemical analysis (W. F. Wight), 

 during the first week in May, 1898, made some investigations on this subject. 

 The outside bark of trees that had been sprayed with Bordeaux mixture 

 was gathered, burned to ash, which was dissolved in nitric acid and the 

 copper plated out on a platinum dish and weighed. The results are cal- 

 culated for 100 square inches of bark surface. The bark of a tree that 

 was sprayed April 18, 1893, gave .124 grains of metallic copper. The bark 

 of a tree more recently sprayed, and on which the spray was still visible, 

 gave .28 grains of copper. The bark of an apple tree sprayed about one 

 year before gave .05 grains, and the bark of a plum tree sprayed about 

 June 1, 1892, gave .044 grains of copper. 



The suggestion has been made that an opinion in regard to the safety in 

 the use of such sprayed fruits as food would not be out of place. The 

 condition where the poisons are applied directly to the fruit a short time 

 before ripening is quite different from that where the poison is applied to 

 one part of the plant while an entirely different part is used for food, such 

 as the application of Paris green to potato vines to kill the Colorado 

 beetle. So also the spraying of the young apples with Paris green soon 

 after the blossoms have separated in order to destroy the larvse of the cod- 

 dlin moth is quite different from spraying the developed and ripening 

 fruit. The persistence with which such poisons adhere to the bark and 

 other surfaces as shown in preceding experiments is quite significant. 



The use of poisons in horticulture in my opinion is largely in excess of 

 the amount required for a fungicide. One half or even one third of the 

 amount usually employed would probably give as good results. 



In the spraying of some fruits, such as strawberries in 1892, the amount 



