358 BOTANICAL GAZETTE [MAY 
50 cc. in 1o-liter chamber; epicotyls 6-13 cm. tall. 
500 cc. in 1o-liter chamber; epicotyls 5-10 cm. tall. 
One liter in ro-liter chamber; epicotyls 4-9 cm. tall. 
Three liters in 6 liters; epicotyls 3-7 cm. tall. 
Two liters in 6 liters; epicotyls 3-7 cm. tall. 
oe eS 
It is evident that the chimney smoke is very slightly toxic. 
In one-half an atmosphere of this smoke the epicoty] is less inhibited 
in growth than in one part in 1000 of the smoke from the loosely 
rolled paper cigarette. This shows that the latter smoke is more 
than 500 times as toxic as the coal smoke used. In commercial 
furnaces it is customary to supply just enough air to oxidize com- 
pletely all gases. Any considerable excess adds to the volume of 
heated air passing out of the chimney and to an economic loss from 
this source. It is in this that the flat-owner can be criticized rather 
than the point in question, the addition of poisonous carbon-bearing 
gases to the air, for his furnace was receiving about 1o times 
the volume of air necessary to give complete combustion. High. 
oxygen supply probably accounts for the small amount of reduced 
carbon-bearing gases and for the low toxicity of the smoke. It is an 
open question in commercial furnaces, where there is little excess 
of oxygen, whether there is a sufficient amount of these gases to 
play any part in the injury of vegetation, as SEARLE (41) has sug- 
gested. In general, the injury from coal smoke has been attributed 
entirely to tars and the oxides of sulphur. It is certain, however, 
that carbon-bearing gases, especially ethylene, might be in sufficient 
concentration to do injury and still be in too small quantities for 
detection by chemical methods (14, p. 257). A full discussion of 
this point is given in the last section of this paper. 
Effect of the various constituents of smoke 
The experiments already recorded afford evidence that the 
heavy hydrocarbons determine the toxic limits of tobacco and paper 
smokes. It is desirable, however, to know the magnitude of 
toxicity of the several constituents, also the nature of the response 
produced in the epicotyl by each. Moreover, it is desirable to de- 
termine the particular hydrocarbon responsible. For paper smoke 
this will demand the study of ethylene, propylene, acetylene, 
