Nov. 12,1917 Greenhouse Fumigation with Hydrocyanic Acid 
333 
Contrary to the findings of the Armstrongs, there was no gain in weight 
from the absorption of water. There was always a loss in weight, but this 
was less marked in normal leaves than in fumigated leaves, and when ether 
or chloroform, and more especially potassium or hydrogen cyanid were 
used, the loss was very pronounced. Fumigated leaves immersed in 
water showed less effect than normal leaves in a solution of hydrocyanic 
acid. Although the successive decrease and increase in permeability 
noticed by Osterhout could not be detected by this method, the very 
marked increase in the case of the leaves soaked in a solution of hydro¬ 
cyanic acid no doubt indicates that the “irreversible increase” has been 
attained. Also, when leaves are ‘ * burned 9 ’ in cyanid fumigation, it means 
that the “differential septa” have lost their power of differentiation, and 
they are disintegrated and the tissue is dead. 
No explanation is offered for the failure of all the leaves under the 
influence of cyanid in Table III to lose sugar to the surrounding medium. 
One would expect the reverse from the fact, first, that respiration is 
below normal, and, hence, sugar is not used up; second, that diastases 
are not prevented by prussic acid from forming more sugar; and third, 
that the sugar if present can escape into the surrounding medium more 
readily because of the more permeable septa. 
EFFECT ON TRANSPIRATION 
Having shown that hydrocyanic-acid fumigation brings about an 
increased permeability in the leaf septa, the writers thought it desirable 
to ascertain how this is related to the wilting effects noticed in fumigation 
injury. 
Water was withheld from a number of potted tomato plants until the 
wilting point was reached. On assuming that this gave all the pots 
about the same water content, 250 c. c. of water were added to each and 
the pot and soil surface thoroughly paraffined. After a preliminary 
test to show that all the plants transpired at about the same rate, 
half of them were fumigated. The dose and length of fumigation were 
varied to produce different degrees of injury. The controls were kept 
under similar conditions in each case. After fumigation the plants 
were removed to the greenhouse and weighed at intervals to follow the 
loss in water by transpiration. 
The results are shown graphically in figure 10. Contrary to what 
was expected the fumigated plants in every case exhibited a diminished 
transpiration. The more severe the injury, the greater was the wilting 
effect and the less was the transpiration. In addition, stomatal measure¬ 
ments disclosed the fact that after fumigation, whether the plants were 
in the light or in the dark, the stomata rapidly closed. Recovery to 
normal transpiration required 24 to 36 hours in the case of plants lightly 
fumigated; severely injured plants, of course, never recovered. 
