1904 | BENNETT: ARE ROOTS AEROTROPIC 245 
We must seek farther for the cause of the curving of these roots 
when growing in a water medium. : 
Other seedlings were grown in water, and placed parallel to 
membranes of immersed gas chambers, as shown in fig.z. In the 
first series of experiments only one gas chamber was used, and 
this contained air. An explanation of the following table, in 
which are recorded the results, will suffice for most of the other 
tables found in this paper. The plus sign (+) indicates a curva- 
ture toward the supply of oxygen, and the minus sign (—) a cur- 
vature away. Only those roots which turned and continued 
thereafter growing toward the air chamber are counted as positive. 
he reverse of this rule is used in determining the negative 
curves. Under the zero sign (0) are classified all other curves 
and roots growing straight. It is noted that of 362 seedlings, 
including those of corn, radish, popcorn, and pumpkin, nearly as 
many turned away from the supply of oxygen, or the air cham- 
ber, as toward it, and more than half (206) were neutral. The 
angles of curvature were slight. 
TABLE I. 
(Plus sign indicates curve toward higher proportion of oxygen.) 
: No. of Period: |T rature Oe: ] 
mpecies Sdieidunie hone = eae + 4 Angle 
Zea Mays (field corn) 86 22-24 22-29° 24 12 50 | 10-45° 
Raphanus sativus. . . 104 24-96 a 33 15 56 | 10-45° 
Zea Mays (popcorn 120 20-24 20-30° 18 36 66 5-90° 
Cucurbita Pepo.... 52 20-24 16-29° 9 9 34 5-60 
ee 362 84 72 | 206 
In the second series of experiments the pressure of carbon 
dioxid was increased above the normal on one side of the root 
by saturating the water frequently with that gas or by passing a 
Slow stream of CO, continuously through the water, other condi- 
tions being the same as in the preceding experiment. It might 
be expected that the roots would turn from the CO, toward the 
Supply of oxygen in the air chamber. The following table 
Seems to indicate faintly such a response, where 39 radish seed- 
lings were positive, as opposed to 24 that were negative or 
indefinite. 
