No. 374.] PLANT MORPHOLOGY AND PHYSIOLOGY. 105 
contents for a given period to a definite amount of gas obtained from a 
solution of 98% (i.e.,c. p.) potassic cyanide in 50% sulphuric acid, KCN 
+H.SO,+ aq. Plants of the Coleus group which we have tried will 
stand in all stages of growth the gas produced from 45% of a gram of 
98% cyanide of potassium per each cubic foot of space for 25 minutes. 
A longer exposure, even for so short a time as 5 or 10 minutes, results 
in more or less injury, and exposure to the gas from ,%°5 gram per 
cubic foot for 25 minutes also results in injury. In the latter case, 
if the time is cut down to ro minutes the plants may stand the 
increased dose without injury. The ratio between the doses and the 
time is not constant. The plants can endure strong doses for a very 
short time much better than they can a weak dose for a long time. 
Under conditions where the stomata of the plant are closed, it can 
resist the gas for a much longer period than it can where they are 
open. The temperature of the chamber also has an important effect. 
If it is high, it increases the diffusibility of the gas and decreases 
the time which the plant can be exposed without injury. If the 
temperature is low, the time may be lengthened. : 
Ferns, eg., Davallias and Adiantums, are able to withstand a 
slightly longer treatment than Coleus. Even the very youngest 
developing fronds are not injured at the upper limit of the treatment 
which would injure the young leaves of Coleus. There are a large 
number of plants of different families which seem to be able to endure 
exposure, as indicated for Coleus and Adiantum, without injury. 
Tomatoes, on the contrary, are very sensitive. All the young growth 
is killed by an exposure of 15 minutes to the gas from 7% of a gram 
of 98% KCN per cubic foot of space. In fact, it is hardly possible 
to give these plants any dose so small that it will not injure some of 
the young growth. The young growth of roses is also remarkably 
sensitive, it being almost impossible to treat them without injury. 
Different varieties of roses, however, seem to differ in this respect. 
The older leaves of tomatoes and roses are much less susceptible. A 
curious effect of the poison was noted on tobacco, on Lilium candidum, ` 
and on tomatoes, where the dose was not great enough to kill the 
plants, but simply to injure them slightly; all the affected cells lost 
their chlorophyll, and, although they continued to divide and grow, 
they were colorless, producing yellowish white blotches in the leaves, 
especially along the veins. In case of woody stems the cells imme- 
diately under the cambium, 77z., the youngest wood cells, were most 
sensitive. In many cases these were killed, much as if by frost, but 
the stems continued their growth. 
