168 GROWTH OF PLANTS 



Ethylene is an excellent anesthetic. Ethylene will anesthetize certain 

 plant organs in concentrations as low as 1 ppm in air. It is interesting, how- 

 ever, that while it anesthetizes one part of the plant, it may start growth in 

 another part. In concentrations far below the anesthetic dosage it still 

 slows the gro\vth, and the inhibition of growth falls very slowly as the con- 

 centration falls. Dilutions of 0.1 ppm of ethylene reduce the rate of elonga- 

 tion of plant organs 25 to 50 per cent, and 0.04 ppm gives easily measurable 

 reduction in rate of elongation. It is likely that much lower concentrations 

 will inhibit elongation in some of the more sensitive plants. 



Butylene, which is almost inactive with plants, will anesthetize centipedes 

 and various insects in concentrations 5 to 40 per cent of the air and partially 

 paralyzes the organisms in higher concentrations; 30 to 75 per cent of 

 propylene is required; and 80 to 90 per cent of carbon monoxide; ethylene 

 and acetylene must be used as a full atmosphere. The most effective of 

 these for insects and centipedes is least effective for plants and the most 

 effective anesthetic for plants is the least effective for insects and centipedes. 



Ethylene is an excellent anesthetic for mammals, lacking as it does some 

 of the undesirable qualities of ether and nitrous oxide. It must be used in 

 high concentration, 80 per cent or a higher concentration, with oxygen. It 

 has been used extensively in surgery. Many anesthetists are very enthusi- 

 astic about its use and others are quite as antagonistic. 



Ethylene induces the decomposition of chlorophyll in the living plant and 

 has been used extensively to hasten the proper coloring of ripe citrus fruits, 

 especially lemons, and to bleach celery. It also hastens many other ripening 

 changes in fruits and has been used commercially for this purpose with 

 tomatoes, bananas, and other fruits. 



Ethylene induces or hastens many other metabolic changes in living 

 plants. These changes are mainly hydrolytic, such as transformation of 

 insoluble protopectins to soluble pectins, higher carbohydrates to soluble 

 sugars, proteins to polypeptides and amino acids. 



Ethylene and the physiologically similar gases induce root and root-hair 

 formation. 



Finally, many if not all respiring plant tissues produce ethylene. The 

 amount of ethylene produced varies greatly with the kind of plant and 

 with the organ of the plant, as well as with the age of the organ. Apples 

 and pears produce much ethylene at the climacteric stage of the fruit; 

 bananas produce less; and the potato tuber little, if any. Since ethylene 

 is produced by plants, often in sufficient concentrations to modify develop- 

 ment, it may be considered a phytohormone. 



Literature Cited 



1. Asmaev, P. G., "The effect of ethylene on the gas exchange and respiration ferments 

 during starvation period of tobacco leaves and other vegetative objects [sic]," 

 Proc. Agric. Inst. Krasnodar, 4 : 100 (1937). 



