Nov. 12, 1917 
Greenhouse Fumigation with Hydrocyanic Acid 
327 
location, as well as the manufacture of starch, is interferred with by hydro¬ 
cyanic-acid fumigation. 
To confirm this point, tomato plants were placed in bright sunlight 
until in the afternoon they showed a high starch content. A number of 
these plants were fumigated in the sunlight with 1 gm. of potassium 
cyanid per cubic meter for 1.25 hours, the control also remaining in the 
sunlight. At the close of the fumigation both sets were placed in the 
dark. Eighteen hours later the unfumigated plants showed that about 
three-fourths of the starch had been removed. The fumigated, however, 
showed apparently no diminution in starch content. Six hours later the 
normal gave but a feeble starch test, while the fumigated set still gave 
a strong test. It required from 3 to 3.5 days for complete disappearance 
of starch in the fumigated plants. Similar trials were carried out with 
other sets of tomatoes and with geraniums, with confirmatory results 
There are two possible explanations of the inability of the plant to 
remove its starch after submission to the influence of hydrocyanic acid. 
One is the inhibition of the diastases, the other is the inhibition of the 
oxidation of sugars in the growing parts of the plant, which would tend to 
maintain the concentration of sugar in the leaves and stems, and thus 
prevent the hydrolysis of starch. 
In regard to the first possibility, it has already been mentioned under 
nonrespiratory enzyms that diastases are not affected by hydrocyanic 
acid. To test the point more accurately, leaf powders were prepared 
from fumigated and unfumigated leaves, and their diastatic activity 
tested quantitatively. One gm. of each of the powders liberated enough 
sugar from soluble starch to reduce 1.04 gm. of copper in Eehling’s 
solution. Hence, there is no detectable effect of hydrocyanic acid on 
this enzym. 
The inhibition of sugar oxidation was determined in the following way. 
A large geranium, plant containing two branches of about equal size 
was selected. About 5 inches of the growing shoot of one branch was 
inserted into a fumigation box through an opening, which was then 
sealed tight. This shoot was fumigated with 1 gm. of potassium cyanid 
per cubic meter for one hour. The plant was then placed in complete 
darkness, and from time to time leaves were removed for a starch test. 
The leaves in the normal branch lost all their starch within 24 hours. 
The basal leaves of the branch the tip of which had been fumigated 
required 48 hours for complete removal of starch. This shows that the 
translocation phenomenon brought about by hydrocyanic-acid fumiga¬ 
tion centers in the growing parts, and thus is primarily a failure of the 
oxidation of food materials in those regions. A few days later it was 
noticed that the axillary buds of the leaves below the fumigated portion 
were awakened into growth just as if the growing shoot had been pruned. 
After attaining a length of about y 2 inch, their further growth was pre¬ 
vented by the recovery of the terminal shoot. 
