i QIS ] 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 in 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 loo firmly by the 

 soil particles. 



B. THE EFFECT ON ROOTS WITH NO SOIL MEDIUM 



i. 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 :_ioo; growth in length somewhat retarded and two other strongly 



