FUMIGATION OF CITRUS PLANTS. 23 



MOISTURE. 



Experiments 4, 6 to 9, and 11, were performed with both dry and 

 wet plants. A comparison of results of these experiments has been 

 presented under the paragraph treating on prefumigation influences. 

 It was found that moisture on plants in prefumigation shade or 

 darkness in no way affects the results where the fumigation is per- 

 formed in shade or darkness. However, where plants were in sun- 

 shine before fumigation it appeared that a wetting with cool water 

 tended to reduce the injury below that normal to dry plants. 



TEMPERATURE. 



Temperature is a factor of much concern during actual fumigation, 

 and has already been discussed in this paper. Its influence is so 

 modified .by the prefumigation and postfumigation temperature and 

 light conditions that it is necessary to pay full attention to these two 

 latter environments in determining the temperature of safety during 

 actual gas exposure. The experiments included in this paper in 

 which plants were at no time exposed to the sunshine, and in which 

 the prefumigation and postfumigation temperatures were within the 

 range of optimum heat conditions, exhibited very little injury where 

 plants were fumigated at temperatures below 80° F. In some experi- 

 ments in which the temperature of fumigation exceeded 80° the 

 injury appeared to be little if any more severe than at lower temper- 

 atures of fumigation, provided the prefumigation and postfumigation 

 temperatures were both low; in other experiments the injury appeared 

 to be greater at the higher temperatures of treatment. When, how- 

 ever, either the prefumigation or more especially the postfumigation 

 temperature was high as well as the actual fumigation temperature 

 the injury was, in general, noticeably more severe than at cooler tem- 

 peratures. This is well illustrated by a comparison of experiment 1 

 with either experiment 14 or 15. Unfortunately none of the experi- 

 ments performed at temperatures exceeding 80° F. were held at a 

 uniform heat throughout the exposure, but the temperature fluctu- 

 ated at least several degrees after the plants were inclosed in the 

 fumigatorium. This condition introduces a secondary factor which 

 must be taken into consideration in drawing conclusions as to the 

 effect of high temperatures on plant injury. 



It appears from a comparative study of the experiments in this 

 paper that severe injury is most noticeable where any two or all 

 three of the fumigation environments, prefumigation, fumigation, 

 and postfumigation, are at high temperatures. In short, if the actual 

 fumigation temperature is high, a minimum of injury is likely to fol- 

 low if both the other environments are- cool. If, however, either the 

 prefumigation or more especially the postfumigation temperature is 

 also high, much more severe injury is likely to result. The evidence 



