1904] BENNETT: ARE ROOTS AEROTROPIC 257 
to insure a moist condition of the gas as well as to aid in deter 
mining the rate of flow. 
In these experiments, pea, radish, and popcorn seedlings were 
used, and in the gas chamber were CO,, hydrogen, or air. 
When CO, was diffusing from the gas chamber during 6 to 12 
hours, and 17 seedlings were used, it was found that 4 were 
curved away from the source of CO,, 5 toward it, and 8 were 
neutral; 4 of those which turned toward the gas chamber grew 
into the chamber through the slits. 
When hydrogen was diffusing from the chamber, 7 of the 12 
seedlings used curved toward the source of that gas. At the close 
of 12 hours it was found that there had been good growth, and 
that 4 roots had grown through the slits into the hydrogen 
chamber. 
When air was diffusing through the slits in the cork plate, 10 
of the 18 seedlings turned toward the air chamber, I away, and 
7 were neutral. 
The gas chamber was thoroughly aerated after each series of 
€xperiments, so that no remnant of the gas previously used could 
influence the results. 
The most interesting results were obtained, however, when no 
special gas was used, but only air at rest both inside and outside 
the small chamber. It was found that under these conditions 
also curvatures were made, 4 of the six seedlings turning toward 
the small chamber containing air, 
Altogether in this series of experiments, in which 53 seedlings 
Were used, regardless of the gases diffusing from the chamber, 
26 turned toward the gas chamber and I! away, while ‘16 
remained neutral. Even more striking was the observation 
that curves appeared in the roots whether or not a gas was 
passed through the slits. It must be very evident from these 
observations that such curvatures are not aerotropic, but are to 
be accounted for in some other way. It seemed not unreason- 
able to conclude that they were hydrotropic curves, and that, as 
the large chamber was probably not thoroughly saturated with 
Moisture, the roots were turning toward the moisture emanating 
from the surface of the cork plate. 
