FUMIGATION OF CITRUS TREES. 53 
damp nights near the coast are exactly as satisfactory as on dry ones. 
Even if the gas is absorbed by moisture the tents become so much 
tighter from being moist that any negative effect from the dampness 
is offset. 
The character of the tenting material used directly affects the dosage 
required. Most of the ducks and drills now used in California (see 
p. 11) are about equally gas-tight. The recommendations of dosage 
given in this bulletin are for these tenting materials. With the 
special new drill experimented with during these investigations (see 
pp. 11-12) one-fourth less dosage is required. Any tenting tighter 
than the cloth commonly used for this purpose in California will also 
require less dosage. 
THE PURPLE SCALE. 
Preliminary experiments to determine the dosage required for the 
destruction of the purple scale were undertaken at Orange, Cal., 
during the month of November, 1907. Orange trees severely infested 
with the purple scale in all stages of development were treated with 
dosage rates varying from three-fourths of an ounce of cyanid per 
100 cubic feet up to 2J ounces per 100 cubic feet. The cubic contents 
of the trees varied but little, the trees ranging from 11 to 14 feet in 
height. The 1-1-3 formula was followed. Exposure lasted one hour. 
After a period of about two months an examination of the results of 
this experiment was made. To show the care with which the exam- 
ination was conducted in this as well as all other experiments against 
the purple scale it might be mentioned that in each case the scales 
were overturned and examined with a high-power hand lens. In 
those instances in which the entire contents of the scale were not at 
once revealed, the delicate ventral scale was ruptured and the con- 
tents scraped out. Through this method not a single egg could 
escape observation. 
As a result of this experiment it was found that all insects were 
destroyed on the leaves and branches by a f-ounce dosage rate, 
that all insects and over 99 per cent of the eggs were destroyed at a 
1-ounce dosage rate, and that all eggs on the leaves and branches were 
destroyed at a 1^-ounce dosage rate. Very little fruit was on the trees, 
yet, where present, normal eggs were found on the fruit after a dosage 
as high as a 1 f-ounce rate. 
In another experiment in which the trees were considerably smaller ; 
some being not more than 7 feet tall, it required a 2-ounce rate to 
eradicate the eggs on the leaves and branches, even though the length 
of exposure was one and one-half hours. This condition shows that 
smaller trees require a much heavier dosage proportionally than large 
trees to offset the leakage of gas, as explained on pages 33-34. 
During July, 1908, an orange orchard near Whittier, consisting of 
about two acres of trees averaging about 7 to 9 feet tall which were 
