1 9 1 9] CLA YTON—FUMIGA TION 493 



A possible role of reducing sugars as determiners of resistance 

 was further tested by arbitrarily changing the sugar content of 

 plants and observing the effects on resistance. 



(i) Plants were placed in a dark box for 48-72 hours. This 

 treatment brings the reducing sugars in the leaves practically to 

 zero at the end of these periods. These plants, when fumigated, 

 were found to be very easily injured. 



(2) Plants treated exactly the same were taken from the dark 

 box 12 hours before the fumigation and infiltrated with a glucose 

 solution. They were returned immediately after the infiltration 

 to the dark box, the exposure to light not exceeding 20 minutes. 

 Plants thus made rich in glucose were highly resistant to cyanide 

 injury. The following are extracts from data collected on this 

 point : 



Fumigation with 0.012 gm. kcn per cubic foot, infiltrated at 9:30 a.m. 



at 6 cm. mercury pressure 

 Dark box plants 



Checks Bad injury 



Infiltrated plants 



. 25 per cent glucose Slight injury 



o. 50 per cent glucose No injury 



1 . 00 per cent glucose No injury (from fumigation) 



Fumigation with o. 14 gm. kcn, infiltrated at 10:00 a.m. at 5 cm. 



MERCURY pressure 

 Dark box plants 



Checks Very great injury 



Infiltrated plants 



0.90 per cent glucose No injury (from fumigation) 



o. 75 per cent glucose No injury 



o . 60 per cent glucose Very slight injury 



With concentrations of glucose o . 9 per cent or above there was 

 some injury to the plants from plasmolysis; such injury was distinct 

 from that due to cyanide and caused no confusion. These experi- 

 ments were repeated many times with uniformly decisive results. 

 Frequently the check plants (not infiltrated) had their entire tops 

 killed, while the treated plants showed little or no injury. 



With these data in hand it is possible to say that for plants to be 

 "normally" resistant they must have a fair content of reducing 



