252 GROWTH OF PLANTS 



than enough sulphuric acid disappears to account for the glutathione in- 

 crease, some other sulphur compound is also synthesized. 



The bud-forcing chemicals " that did not contain sulphur, ethylene 

 chlorhydrin, ethyl alcohol, etc., increased glutathione, which contains 

 bivalent sulphur, much more than do the compounds containing bivalent 

 sulphur, thiocyanates, thiourea, etc. Hydrocyanic acid seems to be an 

 exception. It has about the same forcing action as ethyl alcohol, but un- 

 like the latter causes only a slight increase in glutathione. On the whole, 

 compounds containing bivalent sulphur seem to be important in bud 

 forcing, whether the forcing compounds contain bivalent sulphur or induce 

 the formation of glutathione which contains it. Although it is hard to get 

 into the protoplasm, Guthrie ^^ found glutathione effective in forcing dor- 

 mant buds of potatoes, pears, and peaches, and thinks it may act as one 

 of the effective intermediate chemicals in the forcing action of ethylene 

 chlorhydrin. Certain yeast extracts which are rich in glutathione are good 

 bud forcers, but other chemicals in these extracts are more effective than 

 glutathione. 



The pH of the tubers treated with ethylene chlorhydrin and other non- 

 sulphur but effective forcing compounds " began to rise soon after the 

 24-hour treatment started. This is not caused by the direct effect of the 

 chemical, for ethylene chlorhydrin is slightly acid due to the presence of a 

 small amount of HCl formed by hydrolysis. The fall in acidity is due to the 

 induced consumption of citric acid by respiration and sulphuric and nitric 

 acids in glutathione synthesis. The maximum change in pH Avas reached 

 about 72 hours after the beginning of treatment. The pH change began 

 at the surface of the tuber and worked inward. The maximum change was 

 near the surface and the least near the center. Pieces of tubers free from 

 eyes showed a rise in pH when treated with the chemical. In non-dormant 

 tubers the treatment induced less change in pH. The pH rise, glutathione 

 increase, and the increase in reducing power of the juice ^^ are correlated; 

 the pH rise was partly due to the use of sulphuric and nitric acids in gluta- 

 thione synthesis, and the increased reducing power for the juice, especially 

 for iodine in acid solution, was due in part to the increased sulphydryl in 

 the cysteine of the glutathione molecule. 



Potato tubers held for a long time in storage gradually fall in ascorbic 

 acid (vitamin C) content. The glutathione does not show a parallel fall. 

 Old tubers low in ascorbic acid showed a rise in this chemical after ethylene 

 chlorhydrin treatment."*" The rise was especially fast and the high content 

 was maintained for a long time if the tubers were cut in pieces and exposed 

 to air after treatment. The rise in the cut pieces did not occur if oxygen 

 was excluded from the surface. Fresh tubers with high ascorbic acid con- 

 tent showed no increase in this vitamin after ethylene chlorhydrin treat- 

 ment, but the treatment maintains the ascorbic acid at the high level. 

 There is a marked increase of ascorbic acid in cut surfaces of old untreated 

 tubers but it is maintained for only a few days. There is no correlation 

 between rise in ascorbic acid and sprouting. 



