igi S ] 1IAKY1A y 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 l>v 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 (if 

 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 him 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 



