FUMIGATION OF CITRUS TREES. 11 
tents are exclusively (parts of two outfits excepted) used in southern 
California. A tent of this character is easy to construct, easy to 
repair, and its manipulation has been so perfected by years of use 
that it is very easily handled in the field by intelligent workmen. 
Sizes. — The standard sizes of sheet tents are 17, 24, 30, 36, 41, 43, 
45, 48, 52, 55, and 64 feet, but larger ones up to 72 and 84 feet have 
been employed. The size of this style of tent is properly based on 
the distance between parallel sides, not on the distance between oppo- 
site corners. 
Materials used. — The materials now generally used for sheet tents 
in southern California are 6^-ounce or 7-ounce special drills and 
8-ounce special army duck, though 10-ounce army duck is sometimes 
used in very large tents. These cloths are spoken of in ounces, 
meaning such a weight per yard 30 inches wide. Drills are used as 
freely as ducks. In some other countries where fumigation is prac- 
ticed, notably South Africa, even heavier than 10-ounce cloth is 
sometimes used. This is largely because of its strength and tightness 
of texture. The tendency in California has been to sacrifice tight- 
ness in favor of lightness, as the lighter tents are so much more easily 
manipulated in the field. The main reason for this tendency is prob- 
ably that the practice has been largely in the hands of contract fumi- 
gators rather than in the hands of the growers themselves. The con- 
cerns furnishing the fumigation tents apparently have made no special 
effort to supply the very tightest goods available on the market, prob- 
ably because the profits on these goods would be smaller than on 
the cheaper and more porous cloths. Several of these firms have 
special goods which they recommend for fumigation use. For the 
most part these goods are about on a par as regards the requirements 
for fumigation. Only one grade distinctly superior to the others has 
been seen; it is used solely by private outfits, and is slightly more 
expensive than the other grades. The results secured depend di- 
rectly on the tightness of the cloth; in fact, this consideration of 
tightness of tenting is one of the most important factors in the entire 
fumigation procedure. On it depends not only the efficacy of the 
treatment but also to some extent the cost of the operation. A 
dosage recommended as securing certain results with tents of a given 
degree of tightness will not produce the same results with tents of 
less closely woven material. Even though the initial cost is greater, 
tightly woven material is the most economical in the long run. 
New tenting material. — Considerable attention has been given dur- 
ing this investigation to the character of cloth used in fumigating 
tents, and an attempt has been made to secure the most suitable 
material possible. The leading manufacturers and dealers in cotton 
ducks and drills in the United States were consulted and samples of 
their tightest cloths secured. Many of the nearly two hundred sam- 
