106 GKEEXllOLSE irMIGATlON 



])lants were dry at the l)ei;inning- ctf the funiij^alidn. 'I'he temi)era- 

 ttire was 62° I-\ and the rehitive luimidity 89% (as the temperature 

 outside was much hig^her thau when the previous fumigation was 

 conducted a temperature of 59° F. coukl not be obtained and still 

 permit a drop in temperature in airing out the house). The charge 

 remained in the house for one hour and two minutes when it was 

 airefl out. and the temperature lowered to 57° F. The plants were 

 examined and moisture was found on the lea\es. The plants were 

 injured in a similar manner to those of the previous experiment at 

 least 60% being unfit for market. 



I^ow temperatures during" fumigation are liable to produce 

 injury in still another way. If a house is warm during the day 

 and cooled oft' at night in preparation for fumigation the soil temper- 

 ature will be higher than the air temperature. If the soil is moist 

 the plauts will take up water from the soil faster than they can 

 evaporate it from their lea\es. In many plants such as lettuce, 

 cucuml)ers. tomatoes and others this will produce an exudation of 

 water from the water pores of the leaf. I-igure 24-2. This 

 water takes in hydrocyanic acid during the fumigation resulting 

 in the burning of the edges of the leaves. This type of injury is 

 frequently encountered unless great care is taken to avoid it. The 

 temperattire the day preceding fumigation should be low, increasing 

 to 70° F. at the time of fumigation. No exudation will then occur 

 anless the relative humidity becomes high, which is not liable to 

 occur unless the temperature drops. 



Influence of Temperature After Fumigation. 



A\'hat has been stated to be the influence of the relative humid- 

 ity after fumigation is equally true of the temperature. .\ low 

 temperature acts as a high relatiAe humidity, while a high temi)era- 

 ture acts as a low relative humidity. The temperature no doubt 

 does not produce its results directly^ but by its influence in con- 

 trolling the relative humidity and the evaporation from the plant. 

 Figure 8. 



A high temi)erature will cause the injury from the fumigation 

 to show quicker than a low temperature, l)Ut the hnal injury will 

 be ver}- much less in the case of a high temperature than in that 

 of a low temperature. The reason for this will l)e discussed in a 

 later paper dealing with the action of the h\(lrocyanic acid after 

 it has entered the plant cells. 



