SOME EFFECTS OF ETHYLENE ON THE 
METABOLISM OF PLANTS. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 207 
’ EDWARD Maris HARVEY 
(WITH TWO FIGURES). 
Introduction 
Etiolated pea seedlings develop abnormally when they are 
grown in the ‘‘impure air’? of a laboratory. This response to 
atmospheric impurities has become well known through the 
work of NELJuBow (25) and others. Three phases, at least, 
are usually distinguished in the response of the epicotyl of the 
seedling: (1) a retardation in the rate of elongation, (2) swelling, 
and (3) a change from negative geotropism to diageotropism. 
Furthermore, this characteristic response can be produced by a large 
number of chemical compounds. However, the three phases 
mentioned are not induced with equal ease; the third may never 
appear for a given substance, although that substance readily 
causes swelling and interferes with the rate of elongation. Like- 
wise, both the second and the third may not appear, although there 
is a marked retardation of growth. The swelling of developing 
plant organs in the presence of poisonous substances is a very com- 
mon response, especially when the concentration of the substance 
in question is near the lower toxic limit. So frequently does this 
phenomenon occur that one is perhaps justified in saying that swel- 
ling is one of the first superficial indices of a disturbance in the 
metabolism of a plant. 
Of the large number of chemical compounds capable of inducing 
swelling in the pea seedling, ethylene has been found to be the most 
effective. According to Kwnicut, Rose, and CRocKER (19), 
ethylene will cause swelling of the epicotyl of the sweet pea seedling . 
in dilutions of about 0.00004 per cent (by volume), while to pro- 
duce similar results with chloroform, for example, the concentration 
193 [Botanical Gazette, vol. 60 
