1915} HARVEY & ROSE—ILLUMINATING GAS 29 
the cambium seemed to have become more active. Recently 
STONE (16) has reported proliferations of tissue at the lenticals 
of willow slips growing in water which had been charged with 
illuminating gas. He also noted a rapid proliferation at the 
cambium in stems of Populus deltoides due to the influence of gas. 
Another important phase of the gas injury problem is that after 
trees have been killed by gas, a question arises regarding the safety 
of resetting trees where the dead ones have been removed, assuming, 
of course, that the gas leak has been located and stopped. It 
seems to be the general opinion that resetting should only be done 
either after a considerable time has elapsed, or after large amounts 
of the old soil have been removed and replaced by fresh soil. 
Neither of these methods of procedure is entirely satisfactory; the 
first involves great loss of time, the second is expensive. The 
practicability of resetting trees in any given case is often deter- 
mined only by the crude method of smelling a handful of soil taken 
from the place of injury, and if the odor of gas is still present, 
resetting is deemed unsafe. One is thus led to ask whether the 
odor itself is a true index of the toxicity of the soil to the roots of 
plants. : 
The investigation reported below was undertaken with the two 
problems in mind: (1) that of determining some of the effects of 
illuminating gas on root systems, having in mind the securing of 
further diagnostic characters of gas poisoning; and (2) whether 
the chief causes of injury are those constituents of illuminating 
- gas which are readily absorbed by the water film of the soil particles, 
or those which remain mainly in the soil interstices (not being so 
readily soluble). 
Methods and materials 
The illuminating gas used was the so-called “water gas” from 
the Chicago Gas Light and Coke Company’s system. Along with 
the illuminating gas experiments, many parallel ones were carried 
out with an ethylene-air mixture. The Chicago illuminating gas 
contains 2-6 per cent ethylene; therefore, to facilitate comparison 
between the ethylene alone and the ethylene of the illuminating 
gas, the ethylene of the mixture above was made to constitute 4 
per cent (by volume). Thus, volume for volume, the ethylene-air 
