1913] KNIGHT & CROCKER—TOXICITY OF SMOKE 349 
was more acute, due to longer application and possibly to greater 
concentration of the toxic material. 
EXPERIMENTS 
We will publish only a type experiment under each head, but 
in every case the experiment has been repeated several times to 
make sure the type experiment tells the truth. As has already been 
stated, we used the etiolated epicotyl of the sweet pea as the plant 
organ for testing the toxicity of smoke and its constituents, for 
we learned from our earlier experiments its behavior toward a 
great number of gaseous impurities, including the main constituents 
of smoke. This renders the determination of the constituents fixing 
the toxicity of smoke a simpler matter. Since the responses of the 
seedling to certain smokes and the variation of response with con- 
centration is similar to the behavior toward ethylene, it is well to 
have in mind Netjuspow’s (26) statement of the six types of 
response, varying with the concentration of the ethylene. They 
will furnish the data for an interpretation of the experimental 
results given below. Beginning with the higher concentrations, 
the responses are: (1) no elongation, death; (2) no elongation, - 
vertical position, a knoblike swelling; (3) considerable elongation, 
swelling, horizontal position of the growing swollen part; (4) elonga- 
tion greater, little swelling, horizontal position of part grown in 
ethylene-containing atmosphere; (5) like (4) except obliquely 
placed; (6) erect, but elongation rate reduced by half. Our fail- 
ure to get a strictly horizontal position in many cases where NEL- 
JuBOw obtained it may be due to the fact that he changed the gas 
every day, thus maintaining an essentially constant concentration, 
while we applied the gas once and allowed it to stand for three days. 
The gradual absorption of the gas by plant, substratum, etc., may 
dilute it so that the epicotyl partly recovers its upright position. 
For our purpose, however, one application of the gas is adequate. 
Experiment I.—Effect of unwashed smoke 
When the experiment was set up, the etiolated epicotyls (Gladys 
Unwin) were 2-3 cm. tall, slim and vertical. The duration of 
exposure was three days. The following data show the sorts and 
