a 
——— = 
29 
around some solid object, such as a green orange, about which the 
cloth is gathered. By this means the tent may be caught anywhere 
without the trouble of reversing and turning the heavy canvas to get 
at rings or other fastenings attached at particular points. The two 
remaining members of the operating crew draw the tent up against 
and over one side of the tree by means of the pulley ropes sufficiently 
to cover the other side of the tree when the tent falls. The poles and 
tent together are then allowed to fall forward, leaving the tent in 
position. Sufficient skill is soon acquired to carry out rapidly the 
details of this operation, so that little time is lost in transferring the 
tents from tree to tree, even when the trees approximate the limit in 
height. . A single pair of hoisting poles answers for all the tents used. 
Some of the tents employed are of great size, one described by Mr. 
Havens having a diameter of 76 feet. It is constructed of a central 
piece 50 feet square, of 10-ounce army duck. Four triangular side 
pieces 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 yard wide. The tent is handled by means of ropes 
and pulleys. A 13-inch manila rope is sewed about the border 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 either side of the 
tent. To these rings the pulley ropes are fastened, and the tent is 
elevated over the trees and handled very much as indicated in fig. 4. 
The canvas for the tents, blue or brown drilling or 8-ounce duck, 
may be rendered comparatively impervious to the gas by painting 
lightly with boiled linseed oil. This has the objection, however, of 
stiffening the fabric and adding considerably to its weight; it also 
frequently leads to its burning by spontaneous combustion unless 
carefully watched until the oil is dry. A much better material than 
oil is found in a product obtained from the leaves of the common 
prickly pear cactus (Opuntia engelmanni), which grows in abundance 
in the Southwest. The liquor is obtained by soaking chopped-up 
leaves in water for twenty-four hours. It is given body and color by 
the addition of glue and yellow ocher or venetian red, and is applied 
to both sides of the canvas and rubbed well into the fiber of the cloth 
with a brush. 
Some practical experience is necessary to fumigate successfully, and 
it will therefore rarely be wise for anyone to undertake it on a large 
scale without having made preliminary experiments. 
BISULPHIDE OF CARBON VAPOR. 
In line with the use of hydrocyanic-acid gas is the employment of 
the vapor of bisulphide of carbon to destroy insects on low-growing 
plants, such as the lice on melon and squash vines. ‘The treatment, as 
