24 
ing difficult, but, on the other hand, enables the comparatively heavy 
tents employed in fumigation to be thrown or drawn over the trees 
rapidly without danger of breaking the limbs, One good gassing is 
usually the equivalent of two or three sprayings, the gas penetrating 
to every particle of the surface of the tree and often effecting an almost 
complete extermination, rendering another treatment unnecessary for 
two years or more. 
The gas treatment is just as effective also against scale insects on 
deciduous orchard fruit trees, as has been demonstrated by a good deal 
of work recently done in the East, notably in Maryland by Professor 
Johnson; but the difficulty and expense of the treatment as measured 
by the value of the crop protected makes it as a rule prohibitive in the 
case of deciduous fruits. This does not apply, however, to nursery 
stock, which may be brought together compactly and treated in mass 
































Fic, 3.—Tenting trees for gas treatment, San Diego, Cal, (author’s illustration), 
in fumigating rooms or houses. The general spread of the San Jose 
scale in the East has made such fumigation of nursery stock, even when 
infestation is not shown or suspected, a necessary procedure before 
shipment or sale, to give the utmost assurance of safety to the pur- 
chaser. Similarly this gas is the principal agency employed in disin- 
fecting-plant material coming to California from abroad, and will be 
the chief agency for such work wherever quarantine regulations 
prevail. (See fig. 3.) 
Another very important use for hydrocyanic-acid gas, recently 
demonstrated, isasa means of controlling insect pests in greenhouses and 
cold frames. The process is a special one, however, and entails con- 
siderable of variation, owing to the wide range of plants to be consid- 
ered. The details of the process are given in a special publication of 
this Division (cireular No. 37, second series), which will be supplied 
to anyone interested. 


