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. during 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. In 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 abnormahy 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° hi 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 



