58 
FUMIGATION INVESTIGATIONS IN CALIFORNIA. 
drops of acid might reach the tent. The generator cover described 
above so deflects the gas, and Incidentally such acid as is carried with 
it. that the drops are thrown to the ground, thus saving the tents. 
The decreased cost in mending of tents will doubtless pay for the 
cost of such a cover device several times over in a fumigating season. 
A third advantage, which we have not as vet demonstrated but 
which we have reason to believe will develop, i-> a better distribu- 
tion of gas through the tent. Heretofore the most difficult part of 
the tree in which to destroy insects is the lower part. Thi> is also 
the part of the tree in which the purple scale is largely to be found. 
With the open generator the gas rises straight up in a narrow column 
for several feet (fig. 22. at left), being broken up and distributed 
through the top of the tree 
first. As the gas is lighter 
than air, it is not to be ex- 
pected that it will quickly 
become uniformly distrib- 
uted throughout the bot- 
tom of the tent, even if at 
any time it becomes as con- 
centrated here a- at the top. 
The greater burning effect 
and better killing effect in 
the top of the tree would 
tend to substantiate this as- 
sumption. Field observa- 
tions in fumigating huge 
trees show that the gas is 
of no great strength at the 
lower part of the tent for 
several minutes after the 
charge is set off. With this 
new cover the gas is broken 
Fig. 21.— A cover device attached to a fumigation generator- 
corrugations in cover allow gas to escape. (Original.) 
up and distributed through the bottom of the tent first dig. 22, at 
right). By the time it reaches the top it is pretty generally distiib- 
uted throughout the tent. As the bottom of the tree i> the first to 
receive the full benefit of the gas. a more complete killing of scale at 
the bottom of the tent may be expected than with an open generator. 
AN IMPROVED SYSTEM OF FUMIGATION. 
During the month of July. 1908, a system of fumigation which has 
decided advantages over the old method was introduced into Cali- 
fornia field practice. In this system the tents are marked after the 
Morrill method, described on pages 27-30 (figs. 11 and 12). Only 
the three parallel lines are used, the cross line being unnecessary 
