December, ’23] 
woglum: hydrocyanic acid gas 
521 
generated after the other methods commonly used. If this injury factor 
is neutralized, there is likely to be a further change in the orchard 
fumigation practice. Calcium cyanide has also been tried out as a dust 
on various plants. Flint, in Illinois, has done considerable work with it 
against the Chinch Bug. In California, it is being tried against various 
pests. 
My discussion has been confined to a statement of progress largely 
as illustrating orchard fumigation. There has been great development 
in hydrocyanic acid gas fumigation along various other lines. Between 
1893 and 1900, cyanide gas was successfully used in treating greenhouses, 
nursery stock, stored products, mills and other buildings. Each of these 
methods has experienced great improvement and wider application in 
recent years. No attempt will be made to detail this progress. More 
recently railway cars and ships have been fumigated successfully. 
The development in 1913-1914 of vacuum fumigation by Sasscer and 
Hawkins opened an entirely new and highly important field. Vacuum 
fumigation at once supplied a method of destroying insects in products 
which no other system of fumigation is able to reach successfully. It 
has been found to be the system of fumigation under which insect 
eradication is most certain. Its value in plant quarantine is attested 
by the number of large vacuum plants at .American ports of entry for 
the treatment of foreign products which might contain insect pests. 
In California a number of small plants have been installed for treating 
nursery stock, stored products, et cetera. Vacuum fumigation is as¬ 
sured a great future and its development is proceeding rapidly, especially 
under the guidance of the Federal Horticultural Board. In California, 
Mackie of the State Department of Agriculture has made decided 
progress in the treatment of nursery stock and stored products. 
The environment of insects, as well as of plants, at the time of fumi¬ 
gation has a decided influence on efficiency in insect destruction as well as 
injury to the plant. Valuable data bearing on the influence of various 
factors, such as wind, temperature, moisture, sunlight, Bordeaux mix¬ 
ture, physiological condition of the plant, have been and are being 
developed by entomologists and others, thereby increasing the certainty 
of insect destruction and reducing the hazard to the plant. 
