No. 4.] SAN JOSH SCALE. 307 



jury to the trees except in the ease of the peach and plum. 

 In some cases, however, other species of trees have been de- 

 stroyed, and at the present writing fanners are not advised 

 to make a general use of this remedy until they have first 

 tested it experimentally. 



4. Fumigation. — This method is particularly valuable 

 to the nurseryman. The trees to be treated are loosely 

 packed in a tight room, and exposed to the fumes of hydro- 

 cyanic acid gas for a period of forty-five to sixty minutes. 

 This gas is liberated by the action of acid on cyanide of pot- 

 ash in water. The necessary quantities of the ingredients 

 for one hundred and fifty cubic feet of space are : cyanide 

 potash (ninety-eight per cent), one ounce; sulphuric acid, 

 one ounce ; water, three ounces. The cubic contents of the 

 fumigation house is computed, and the necessary amounts of 

 chemicals prepared. The water and cyanide are placed in a 

 suitable earthen dish such as a bean-crock or other wide- 

 mouthed receptacle, and when all is ready the acid is poured 

 into the mixture and the doors closed for the time indicated. 

 Before removing the trees the chamber must be allowed to 

 ventilate, since the gas is fatal to human as well as insect 

 life. 



A simple yet effective fumigation house built by one of 

 our nurserymen consists of a double-boarded building, ten 

 feet wide and thirty feet long. In this building there is a 

 chamber ten by twenty feet for the fumigation of large quan- 

 tities of stock or of tall trees, while two smaller chambers, 

 five by ten feet, afford means for fumigating shrubs and small 

 trees. After the fumigation house has been erected, the 

 labor in handling the stock is the chief item of expense. 

 Cyanide of potash costs thirty-eight cents per pound in 

 quantity, and sulphuric acid less than two cents per pound. 

 Professors Alwood of Virginia and Johnson of Maryland 

 have had extensive experience in fumigating nursery stock, 

 and both find that when properly conducted the fumigation 

 treatment is an exterminative measure. From the testimony 

 of many experts it is evident that in fumigation we have the 

 best-known means of insuring the freedom of nursery stock 

 from the scale. 



