26 BULLETIN 907, U. S. DEPARTMENT OF AGRICULTURE. 
experiment 27 the temperature was suddenly raised during the initial 
exposure to the gas from 54° to 70° F., a rise of 16°, and fluc- 
tuated within the range of 61° to 70° F. durmg the exposure. It 
would appear that the shock to the plant resulting from this sudden 
rise in temperature during the gas exposure accounts for the greatly 
increased injury in experiment 27 over that in experiment 3 or 
experiment 8. ; 
The effect of a sudden rise of temperature is also shown in experi- 
ments 24, 25, and 26, all of which were performed at temperatures 
ranging from 86° to 92° F., which are much higher than that of 
experiment 27. An examination of experiment 25, in which the pre- 
fumigation temperature was 65° F. and in which part of the postfumi- 
gation conditions were equally favorable, shows that the injury is very 
severe irrespective of prefumigation or postfumigation environment, 
in all cases a large proportion of the most resistant leaves being 
destroyed. The degree of plant injury was much greater than that 
in experiments 14 and 18, which were performed at equally high 
temperatures with the same dosage and exposure. Jn experiment 25 
the temperature was quickly raised 19°, from 73° to 92° F., imme- 
diately before generating the gas, and was maintained between 86° 
and 92° F. throughout the treatment. This sudden rise in tempera- 
ture, supplemented by fluctuation during the exposure, appears to 
be the cause of abnormally severe plant injury. ‘The results in experi- 
ments 24 and 26 are in full accord with that in experiment 25, and 
corroborate the influence of a sudden rise of temperature immediately 
before and during the exposure of plants to hydrocyanic-acid gas. 
Experiments 14, 15, and 18 also fall within the class of tests in 
which the temperature was raised during the exposure of plants to 
the gas. The injury in these experiments is comparatively less than 
in Nos. 24 to 27. 
An examination of the data presented in this paper shows that all 
experiments performed at high temperatures (above 85° F.) indicate 
a greater degree of injury, in general, than where plants are treated 
at cooler temperatures. In each of these experiments the high tem- 
peratures were attained by increasing the heat artificially during the 
gas exposure. ‘These sudden increases in temperature during the 
fumigation exposure varied from 10° in experiment 14 to a maximum 
of 28° in experiment 24. Furthermore, after increase to the maxi- 
mum temperature, fluctuations took place during the actual gas expo- 
sure ranging from 2° in experiment 14 to 10° in experiment 27. This 
condition of sudden rise in temperature, especially when accom- 
panied by wide fluctuation during the exposure, appears to exert a 
highly injurious influence on the plant. Where the rise of tem- 
perature was only 10° to 14°, as in experiments 14 and 18, and was 
held during the exposure with slight fluctuations of 2° to 4°, the 
