440 BOTANICAL GAZETTE [NOVEMBER 
The reaction itself is very easily observed. The most obvious 
effect of the gas is the nastic drooping of the leaves as mentioned 
above. This drooping is brought about by curvatures, located 
either at the inner or at the outer end of the petiole or at both. 
If the gas be of certain concentration, the older leaves may develop 
abscission layers that often result in leaf fall. And again, if the 
gas be somewhat stronger, rapid proliferation may take place at 
these new leaf scars, forming small masses of tissue which usually 
exude sap. The most delicate response of the plant seems to be 
a nastic folding down of the laminae of the young leaves. However, 
the very young leaves that are still more or less enveloped by the 
bud scales seldom show any response. 
Data regarding the appearance and degree of these responses 
were obtained by observation of the following points. Previous 
to the exposure, the leaves of the plant were numbered consecu- 
tively from cotyledons upward. Also the condition and direction 
of the plane of the leaves were noted. This consisted in an examina- 
tion for abscission layers already started, the measuring of the 
angle made by each petiole with the stem, and the angle made by 
the plane of the leaf surface with the petiole. After exposure, 
examination was made for leaf fall, starting of abscission layers, the 
new angles made by the petioles with the stem and by the plane of 
the leaf surfaces with the petioles, and, finally, the condition of the 
laminae of the young leaves was noted. The amount of nastic 
drooping at each end of the petioles was recorded in degrees. 
The results of the experiments proved that this plant has 
great capacity for response to low concentrations of ethylene, just 
as one was led to expect from its common behavior in the laboratory. 
The lowest concentration tried was one part ethylene to 10,000,000 
of air (or 0.00001 per cent). With this amount the response 
was absolutely definite, as shown, for example, in one case by a 
nastic drooping of 15° at the inner end of the petiole for leaf no. 5; 
by drooping of 30° and 15° at the outer ends of the petioles for 
leaves nos. 5 and 6 respectively; and by a nastic folding down of 
laminae for leaves nos. 6 and 7. Parallel experiments with illu- 
minating gas and ethylene, where the ethylene constituent of the 
former was about equal to the ethylene in the corresponding 
