1904] BENNETT: ARE ROOTS AEROTROPIC 253 
saturated, the gelatin containing the hydrogen, or CO,, remain- 
ing in the air-tight chamber of that gas from which it had not 
been removed at any time during the operation. 
Two of these blocks of hardened gelatin (jig. 4, ¢ and e), 
removed from the rectangular molds and freed of all unnecessary 
paper, were trans- 
ferred quickly to a 
damp chamber (A), 
lined with moist fil- 
ter paper dipping 
into several centime- 
ters of water (D) in 
the bottom of the 
jar. The gelatin 
blocks were placed 
on their narrow sides Fic. 4.—d, damp chamber; D, hele Soe 
on raised platform 6,8 Me ne pe pat 
of glass (C) SUP- wooden bar; 4 rubber tubing. 
ported in the bottom 
of the jar, so that their broad sides were vertical and facing 
each other. Seedlings, supported in the usual manner on the 
bar of wood, were now quickly placed between the blocks of 
gelatin, the latter were pressed together and held firmly in the 
vertical position by means of glass plates (a and a) and wooden 
bars (d and d), at their backs, the latter pressing at both ends 
against the sides of the damp chamber. 
It may be seen from Table VI that in the first two sets of 
seedlings the gelatin was not thoroughly saturated with CO,. 
Under such circumstances the difference in oxygen pressure on 
Opposite sides was not great, and the seedlings had ready access 
to a sufficient oxygen pressure for good growth, but made no 
definite curves. In the other sets, in which the gelatin was 
thoroughly saturated with CO, or hydrogen, the oxygen pressure 
was not sufficient for good growth. Here again none of these 
roots showed curvatures of any definite character. : 
A still further trial, however, was made by supporting the 
roots in a very thin septum of gelatin and allowing gases to dif- 
fuse through the gelatin from the opposite sides. 
