774 Hall, Miller, and Herrero 



vinced us that ethylene is produced by an oxidative reaction which is 

 very closely related to the total consumption of oxygen. The second 

 point is that there evidently is a sequence of reactions in the forma- 

 tion of ethylene of which oxidation is only a part. In pure nitrogen 

 there is a very small production of ethylene, limited to the first 20 

 minutes or so, and after that it ceases. If tissues which have been 

 anaerobic for 4 or 5 hrs. are exposed to oxygen for 5 min. only and 

 again returned to nitrogen, those few minutes of oxygen allow a very 

 considerable production of ethylene afterwards in nitrogen. There is 

 evidence for the accumulation of an intermediate in nitrogen which 

 afterwards is converted in oxygen to a precursor of ethylene.^ Some 

 experiments with tritiated water strongly suggest that one of the 

 terminal reactions is a reversible dehydration because the tritium is 

 incorporated into ethylene just about as rapidly as into the tissue 

 water. Lastly, there are very peculiar osmotic phenomena concerned 

 with ethylene production. W'e early found that slices of apple tissue 

 are very different from slices of potato tissue or indeed from slices of 

 any other tissue with which I am familiar in that when placed in 

 water they do not become turgid. On the contrary, they leak and lose 

 a considerable quantity of their constituents. This has some advan- 

 tages in that they can take up complex organic substances. But their 

 turgor diminishes and simultaneously they lose to a great extent their 

 ability to produce ethylene. On the other hand, in low concentrations 

 of a solute they become tingid, and this is particularly well shown in 

 glycerol. In higher concentrations of solute they become flaccid again. 

 A plot of the increase or decrease in fresh weight of the tissue, as a 

 function of the glycerol concentration, shows that in water, they ac- 

 tually lose water. They gain water in moderate concentrations of 

 solute, and in high concentrations they are plasmolyzed. The effect of 

 these changes on the ethylene production is unexpected; in water, 

 ethylene production goes down just as does the water-holding capacity, 

 in the intermediate concentrations it goes up, and finally in the high 

 concentrations it remains up. That is to say, the tissue can be per- 

 fectly plasmolyzed and flaccid and yet it produces ethylene at the 

 full rate. On the other hand, if it is flaccid due to soaking in water 

 it produces ethylene at less than half the control rate. Thus although 

 the system is osmotically very sensitive, it is not sensitive to the 

 water content of the cells themselves, but rather to the osmotic state 

 of something inside the cells. KCl reacts exactly like glycerol, and 

 CaClo is a little less effective. This phenomenon and the very close 

 relationship to oxygen consiunption strongly suggest that the osmotic 



^See S. P. Burg an.l k. V. Thimann, Proc. Nat. Acad. Sci. 45: 335-344, 1959; 

 Pl;ini Pliysiol. (In preparation.) 



