166 GROWTH OF PLANTS 



time when kept at cold storage temperatures, is 0.57-0.78 ml per kg-day. 

 The maximum rate of respiration for Bartlett is approximately double that 

 for Anjou. Under anaerobic conditions, the production of ethylene is 

 either greatly retarded or entirely inhibited. In the fruits used for these 

 experiments, there was found but little difference in the production of CO 2 

 under aerobic and anaerobic conditions. The maximum rate of ethylene 

 production occurs at 20° C. At higher temperatures production decreases 

 and is totally inhibited at 40° C. Respiratory activity as measured by 

 either CO2 production or O2 consumption is greatly accelerated between 

 20° and 40° C." 



The question naturally arises whether living plant tissues produce the 

 other effective gases: acetylene, propylene, and carbon monoxide. As has 

 been stated above, wherever the minimum effective concentrations of the 

 several gases for producing a plant response have been determined, ethyl- 

 ene has proved effective in very much lower concentrations than the other 

 gases. Hansen and Christensen ^'* state that solubility tests indicate that 

 ethylene is the active gas evolved by the fruits, with similar unsaturated 

 hydrocarbon gases, such as acetylene, propylene, and butylene, not present 

 in sufficient amounts to be detected by the bromination procedure. Lang- 

 don ^^ found that the atmosphere in the float and air channel of giant kelp, 

 Nereocystis leutkeana, is 1.1 to 12.2 per cent CO, varying widely from plant 

 to plant and little with time of day. Langdon and Gailey ^^ believe the CO 

 is a product of aerobic respiration, since it occurs only when oxygen is 

 present and equally abundant in light and darkness. Rigg and Henry ^* 

 confirm the previous work on the origin of the CO in the kelp. As we have 

 seen, the concentration of CO in the kelp float is sufficient to cause many 

 formative changes in various plants. We have no evidence, however, that 

 CO is produced by most plants and even if it is, probably not in sufficient 

 concentration to have formative effects. The same is true of acetylene, 

 propylene, and butylene. 



Since plant products, especially fruits, produce ethylene which has 

 marked physiological effects upon other living plant organs, some dis- 

 crimination must be used in storing various plant products in proximity to 

 each other. Cut carnations ^^ in cold storage rooms with apples become 

 sleepy. Ripe apples and high ethylene-producing apples ^^ hasten the 

 respiration and ripening of slow-maturing apples stored with them. A 

 number of storage practices may be modified by these findings on the 

 production of ethylene by plants and the effect of ethylene on plants. In 

 the case of apples being used to defoliate roses, ^* the association is beneficial. 



Summary 



The researches described above and carried out mainly in the United 

 States have shown that ethylene, acetylene, propylene, and carbon mon- 

 oxide have many far-reaching and interesting effects upon plant develop- 

 ment and plant metabolism. These researches were early stimulated by the 



