74 HYDROCYANIC-ACID GAS FUMIGATION IX CALIFORNIA. 
THE PRESENCE OF OLD SCALES ON FUMIGATED TREES. 
Scales do not fall from the different parts of a tree as soon as 
destroyed. On young and growing fruit they are easily shed, but they 
may cling to the old fruit, leaves, and branches of trees until removed 
by mechanical means. Dead purple scales probably cling to the 
different parts of a tree much more generally than any of the other 
common citrus pests. Leaves, branches, or old fruit severely infested 
will normally remain so as long as they continue to be a part of the 
tree. This condition leads many growers to condemn a treatment as 
unsuccessful because on examining a tree long after the operation 
scales are found present. The mere presence of scales may incorrectly 
indicate to them that they have not been destroyed. 
The prevalence with which successive generations of scale insects 
exist simultaneously on citrus trees renders it impracticable and really 
impossible to draw conclusions in exact percentages as to net results 
of experimental work whenever the results fall short of eradication. 
At the time of the treatment the scale on some leaves might all be 
alive, while on other leaves the majority may be dead, and with all 
gradation between to be found elsewhere. 
A DEVICE FOR COVERING FUMIGATION GENERATORS. 
During the course of this investigation much attention has been given 
to perfecting a device for attachment to the top of the commonly used 
open-style fumigation generator that will serve to interrupt the direct 
rise of the hydrocyanic-acid gas. The result of these efforts, in which 
the writer was greatly aided by Mr. Frederick Maskew, is shown in 
figure 12. The device itself consists of a copper cover of such size as 
to make it available for use with any of the regular-pattern generators 
now employed by the fumigators of southern California. It is stamped 
in a concave form from a sheet of copper, with corrugations to per- 
mit the escape of gas. The shape is such as to conform to the size of 
the opening of generators of different capacities and also to direct the 
course of the escaping gas downward and distribute it uniformly 
through the lower part of the tent. It is attached to the generator 
by hinges of stout copper wire secured by a key bolt passing 
through the handle. The cover is raised by a slight pressure of the 
thumb on a projecting piece which is curved in such a manner that 
the cover will remain in an upright position when so required. When 
the generator is emptied of its contents, the cover swings clear by its 
own weight. A glance at the illustration will satisfy the practical 
fumigator that it is adapted to all the requirements of rapid work in 
the dark, while its use has demonstrated that it is simple, strong, and 
durable. It is very possible that if the copper cover were lined with 
a thin covering of lead its durability would be increased. A common 
