1915] HARVEY & ROSE—ILLUMINATING GAS 33 
be a greater development of anthocyanin in the treated soils. At 
the close of the experiments, the treated soils always gave a notice- 
able gas odor and in most cases the odor was very strong. 
The results of these experiments would indicate that of the con- 
stituents absorbed from illuminating gas by soil, those which give 
the odor to the gas are very prominent, and when once absorbed 
are held for extended periods, even after the soil is freely exposed’ 
to the air. But the most important fact from the standpoint of 
the question in hand seems to be that these odorous constituents 
are evidently not extremely toxic to plant roots growing in the same 
soil. The plants tried in such soils included a wide range in regard 
to relationship, and also they were taken at what is considered the 
critical stage, that is to say, the germinating and young seedling 
stages. Just what these odorous compounds are is an interesting 
question. The odor of any illuminating gas is probably the 
combined odor of a number of substances, for example, pyridine, 
thiophene, picoline, quinoline, cumene, cymene, and others. Very 
little is known concerning the effect of these on vegetation. 
CROCKER, KNIGHT, and Rose (3) found cumene, thiophene, and 
pyridine were many hundred times less effective in reducing growth 
in the etiolated sweet pea seedlings than was ethylene. 
The results of the experiments described indicate that the 
presence of a gas odor in soil is not an index of its toxicity for 
vegetation, and that odors would be valuable merely as a means of 
determining whether or not illuminating gas had been in the soil. 
With regard to using odors in diagnosis, CROCKER has suggested 
to us the possibility of distilling (at high temperature im vacuo) 
soil from places where gas injuries have been suspected, but 
where the odor even at the time is not discernible, thereby 
drawing off some of the odors previously held too firmly by the 
soil particles. 
B. THE EFFECT ON ROOTS WITH NO SOIL MEDIUM 
1. With roots alone exposed 
Material, seedlings of Vicia Faba. Exposure period five days. 
With illuminating gas—(1) Concentration 1:4000; no effects 
were noted, evidently grew as well as controls; (2) concentration 
1:400; growth in length somewhat retarded and two other strongly 
