40 



By these tests we concluded (l) that nursery stock and young trees 

 of one and two years old to be replanted should be exposed to the 

 gas for thirty minutes or longer and (2) that from 0.18 to 0.25 grams of 

 potassium cyanide should be used for every cubic foot of air space 

 inclosed. On large bearing trees 0.20 grams of cyanide gave us the 

 best results. 



At first the amount of acid we used was the same as the cyanide, 

 while the water was three times that quantity. We followed this for- 

 mula, as it had been generally used and recommended in California and 

 by the United States Department of Agriculture at Washington. Our 

 results however were not satisfactory. The cyanide in all cases did not 

 act as it should, and the residue was at times blackish instead of being 

 bluish or milky. We then began a series of experiments to determine 

 the relative amounts of acid and water to use with a given amount of 

 cyanide in order to get the best possible results. At last we observed 

 that our results were satisfactory where we used a half more acid than 

 cyanide and a half more water than acid. In other words, if I used 2 

 ounces of cyanide I would require 3 ounces of acid and 4J ounces of 

 water. 



Having concluded these tests, I again began my work upon young 

 trees in March, 1897, and continued it until April 15 of that year. All 

 the trees used for these experiments were badly infested, and after 

 fumigation were set out in an isolated field and watched carefully 

 throughout the spring, summer, and fall of 1807 and spring of 1898. 

 Up to the present time I am happy to report not a living scale has 

 been detected upon any trees except those used for checks, all of which 

 were destroyed June 7, 1897, at which time the first young appeared. 



So conclusive and satisfactory were these results, I was prompted to 

 begin an extensive experiment in a nine-year-old pear orchard the fall 

 of 1897. My equipment, perhaps the most extensive of the kind ever 

 gotten together in the East, consisted of twelve tents Two of these 

 were kindly loaned by Dr. L. O. Howard, United States Entomologist, 

 two more were bought by the Maryland Experiment Station, and eight 

 were secured through the generosity of Capt. Robert S. Emory, one of 

 Maryland's most successful and enterprising fruit growers. With this 

 equipment of tents, 150 pounds of cyanide, and 3 carboys of sulphuric 

 acid I began an experiment full of almost insurmountable difficulties. 

 Although successful upon citrus trees in California, it was an open 

 question whether the gas method could be used economically and to 

 advantage in deciduous orchards in the East and South, where climatic 

 and local conditions are very different. Anxious to settle this question 

 beyond all doubt, I set out to determine the following points: 



(1) The physiological effect of the gas upon the tree. 



(2) The effect of the gas upon the San Jose scale. 



(3) The practical utility of this method in large growing orchards in 

 the East and South during all kinds of weather conditions. 



To determine the first two points many preliminary experiments were 





