PHYSIOLOGICALLY ACTIVE GASES 



159 



R. B. Harvey ^^ recommends the use of ethylene, 1000 ppm or more 

 dilute, for blanching celery. Acetylene was less effective. Hibbard ^^ con- 

 firmed Harvey's conclusions that ethylene hastens the blanching of celery, 

 but found that it also reduces the growth. It hastens the yellowing of the 

 green part of Mcintosh apple skin but had no effect on the development of 

 the red pigment. Other investigators have found that ethylene hastens 

 several other ripening processes in fruits. These will now be described. 



Figure 60. At left: control. At right: leaves of Rosa (hybrid tea) variety Madame 

 Butterfly showing the yellowing of the veins of leaflets 3 days after removal from a 

 48-hour treatment in 1 : 5000 illuminating gas. 



Other metabolic changes in living plant tissues. E. M. Harvey ^® was 

 one of the early workers to make a detailed study of the effect of ethylene 

 upon the metabolism of plant tissues. He also reviewed the earlier literature 

 on the effects of anesthetics upon plant metabolism. He grew inch-long 

 epicotyls of the sweet pea for 72 hours in air containing 1 ppm of ethylene 

 and compared the chemical composition of these with epicotyls gro^\Ti in 

 air. Ethylene caused the simple soluble substances to increase at the 

 expense of higher soluble and insoluble forms. Sugars, amino acids, amides, 

 polypeptides, lipoids, etc., soluble in hot alcohol-ether, increased 8 to 9 per 

 cent while the insoluble substances — proteins, starch, cellulose, ligno- 

 celluloses, etc. — showed a corresponding decrease. Reducing sugars in- 

 creased about 11 per cent and non-reducing sugars decreased about 

 3 per cent. Amino acids plus amides increased and the polypeptides de- 

 creased. The fats were lower in the treated epicotyls and the cellulose and 

 proteins were about 3 per cent lower. The acidity was not changed. 

 Respiration was lowered, the author believed, because the ethylene was 



