Nov. 12, 1917 
Greenhouse Fumigation with Hydrocyanic Acid 
335 
exchange in the leaf is in favor of the cuticular transpiration, and wilting 
results. If the disturbance in the osmotic relations does not reach the 
stage of “irreversible increase in permeability” described by Osterhout 
(16), the leaf will in time recover its normal turgescence. If it exceeds 
that point, however, the leaf is “burned” and dies, as was discussed 
above under permeability. 
In order to demonstrate in another way that the septa of injured 
leaves are made equally permeable to solutes and to solvent, or, in other 
words, are “permeable” instead of “semipermeable,” the experiment 
was tried of forcing water into wilted plants to cause them to recover 
their turgidity (17, p. 232). A plant was cut off at the base and the 
stem sealed into one arm of a U-tube. This arm was filled with water 
and the other with mercury. Normal 
tomato plants so wilted that they had 
bent completely over were forced into ^ 
an upright turgid condition by 12 cm. 
of mercury within 10 minutes. Plants 
wilted by hydrocyanic add, however, 
did not respond to the treatment. 
The less injured leaf blades would 
partly recover, and the petioles com- Fig. ii. —Curves showing the cuticular tran- 
pletely; the more severdy injured spiration of fumigated and of normal tomato 
blades would remain limp and grad¬ 
ually curl and shrivd, and the “burned” petioles also would fail to 
respond even slightly to the pressure. 
CONCLUSIONS 
From the data presented it may be stated that plants subjected to 
hydrocyanic-acid fumigation absorb more or less of the gas; that the 
immediate effect of the presence of this poison is a reduction in the 
activity of the oxidases and catalase, and, hence, in respiratory activity. 
Resulting from this is an inhibition of photosynthesis and translocation 
of carbohydrate, and a closing of the stomata. Another result is an 
increase in the permeability of the leaf septa, which causes less rapid 
intake of water from the stems and more rapid cuticular transpiration. 
In cases of mild fumigation this results in merely a temporary wilting; 
in more severe fumigations the wilting is followed by disintegration and 
death of the tissues. This increased permeability is no doubt due to 
the reduced respiratory activity. Budgett (5) has shown that changes 
in the permeability in protozoa treated with cyanid are similar to those 
produced by lack of oxygen. Within a few hours after fumigation the 
oxidase activity has returned to normal, while the catalase and the 
respiratory activities have exceeded the normal. By this time the 
recovery of photosynthetic action is first apparent; complete recovery, 
however, of this and of translocation of food material is not attained 
before from tw T o to three days. Respiration remains above normal for 
