14 



For small trees ordinary earthenware vessels may be used to generate 

 the gas. For large trees requiring heavy doses tall wooden pails have 

 proved more practicable, two generators being employed for the very 

 largest trees. It is important that the water be put in the vessel first, 

 and then the acid, and lastly the cj^anide. If the water and cyanide 

 are put in the vessel first and the acid poured in afterwards there is 

 danger of an explosion, which will scatter the acid and burn the tents 

 and the operator. In the spring, when the trees are tender with new 

 growth, and in early fall, when the oranges are nearly grown and the 

 skins are liable to be easily marred, and also with j'oung trees, it is 

 advisable to add one-third more water than ordinarily used, or use the 

 cyanide in larger lumps. This causes the gas to generate more slowl}" 

 and with less heat, and if the tents are left over the trees a third 

 longer the effectiveness of the treatment will not be lessened. 



The extremely dangerous nature of the gas must be constantly borne 

 in mind and the greatest caution should be taken to avoid inhaling it. 

 The person handling the chemicals should always have an attendant 

 with a lantern, to hold up the tent and enable the c}' anide to be quicklj^ 

 dropped into the generator and to facilitate the prompt exit of the 

 operator. 



As with spraying, the gassing is often done (and this is very desira- 

 ble also) by individuals or companies who make a regular business of 

 it, charging a fixed rate per tree, depending on size — from 10 cents to 

 a dollar or more. Much of this work is also done under the direct 

 supervision of the county horticultural commissioners, which gives a 

 greater assurance of efficiency. 



Practicallj^, the only tent now used is the so-called "sheet tent," 

 which is drawn up over the tree by means of pulleys (figs. 1-3). For 

 very large trees, averaging 30 feet in height, it is sometimes necessary 

 to employ two sheets to effect a complete covering. 



Some of the tents employed are of great size, the one illustrated in 

 the figures, from photographs secured by Mr. Havens, having a diam- 

 eter of 76 feet. As described by Mr. Havens, it is constructed of a 

 central piece 50 feet square, of 10-ounce army duck. Four triangular 

 sidepieces, or flaps, of 8-ounce duck, 10 feet wide in the middle, are 

 strongly sewed to each side of the central sheet, forming an octagonal 

 sheet 70 feet in diameter. About the whole sheet is then sewed a strip 

 of 6-ounce duck, 1 j^ard wide. The tent is handled by means of ropes 

 and pulleys. A l^-inch manila rope is sewed about near the edge of 

 the central piece in an octagonal pattern. Rings are attached to this 

 rope at each of the eight corners thus formed, and also on opposite 

 sides of the outer edge. To these rings the pulley ropes are fastened 

 and the tent is elevated over the tree and handled as indicated in the 

 plates. 



The treatment is made altogether at night, although it would be 



172 



