Tg15] HARVEY & ROSE—ILLUMINATING GAS 43 
perhaps adding one more line of evidence. Another change found to 
take place under the influence of low concentrations of illuminating 
gas was the disappearance of starch from the cortex of the roots, 
an observation in agreement with that of Richter (12) and others. 
Summary 
1. When illuminating gas is passed through soil, the odor- giving 
constituents of the gas are readily absorbed by the soil particles 
and strongly held. . : 
2. These odorous substances are very slightly, if at all, toxic to 
roots of plants growing in a soil containing them. 
3. The constituents of illuminating gas which remain in a gase- 
ous state in the soil interstices are the chief cause of injury to root 
systems. 
4. Among these constituents, -etelene is probably the most 
harmful, except in extremely high concentrations of illuminating 
gas, where the toxicity of other substances, together with other 
factors, would be expected to play a part. 
5. Low concentrations of gas induce abnormal cab ee of 
tissue. 
a) Illuminating gas.—These abnormalities appear in certain 
tree seedlings within 8-21 days, with concentration one part 
illuminating gas to four parts air (air of the soil), or as low as one 
part illuminating gas to forty of air. 
Ethylene——This gas alone, when used in Smcnrations 
corresponding to the ethylene content of the illuminating gas used 
in the tests, gives abnormalities similar in type and degree. 
6. High concentrations of illuminating gas result in the rapid 
killing of the roots, and the only symptom of injury to be observed 
is death. 
7. If illuminating gas is allowed to flow very slowly through a 
soil in which woody plants are growing, abnormal tissue develop- 
ment in the root will very often ensue. 
8. In low concentrations of illuminating gas, hydrolysis of 
Starch and some other related chemical reactions are accelerated. 
9. It was found that, by use of the etiolated sweet pea seedling, 
small amounts of illuminating gas in the soil could be detected where 
the odor of gas was indistinguishable by the usual methods. 
