—— a Soe 
27 
The duration of the treatment indicated in the second table varies 
with the size of the tree, but in general at least forty minutes should 
be allowed. 
General directions for orchard fumigation.—The first table indicates 
for the smaller trees twice as much cyanide and acid as was formerly 
advised, and for the larger trees three times the formeramounts. The 
second table indicates a considerable increase over the first, and three 
or four times as much of the chemicals as was generally recommended 
as late as 1898. The greater expense entailed by this larger quantity 
of chemicals is offset by the more effective results and the consequently 
longer intervals between treatments. Mr. Havens suggests that for 
small trees ordinary earthenware vessels may be used to generate the 
gas. For large trees requiring heavy doses, tall wooden pails have 
proven more practicable, using two generators for the very largest 
trees. It is important that the water be put in the vessel first, and 
then the acid, and lastly the cyanide. 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 young trees, it is 
advisable to add one-third more water than ordinarily used, or the 
cyanide in larger lumps. This causes the gas to generate more slowly 
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 treatment is made at night, and the person handling the chem- 
icals should always have an attendant with a lantern, to hold up the 
tent and enable the cyanide to be quickly dropped into the generator, 
and to facilitate the prompt exit of the operator. 
Trees are fumigated for the black scale in southern California in 
October, or preferably in November. The red and other scales may 
be treated with gas at any time, but preferably at the season already 
alluded to. In California most of the work is done by contract, or 
under the direct supervision of the county horticultural commissioners, 
in some cases the tents and material being furnished at a mere nominal 
charge, together with one experienced man to superintend the work, 
while a crew of four men operate the tents, the wages of the director 
and men being paid by the owner of the trees. 
Construction and handling of tents.—The tents now employed are of 
two kinds, the ‘‘sheet” tent of octagonal shape for large trees, and 
the ‘‘ring” tent for trees under 12 feet in height. The ring tents, or, 
as they are also called, the bell tents, are bell-shaped and have a hoop 
of half-inch gas pipe fastened within a foot or so of the opening. Two 
men can easily throw one of these tents over a small tree. An equip- 
ment of 36 or 40 ring tents can be handled by four men. They are 
rapidly thrown over the trees by the crew, and the director follows 
