1902] THE RHEOTROPISM OF ROOTS 267 
_ The foregoing table does not tell the whole story. The 
roots in the velocities above 2°" per minute had the character- 
istic appearance of rheotropic responses, the apical part of the 
root being bent in a curve. The roots in velocities below 2™ 
per minute showed mere inclindtions and not curves. Moreover, 
the bent roots in the higher velocity were in 80 per cent. curved 
only in a plane parallel with the current, while nearly all the 
bent roots in the lower velocity were curved either in planes 
oblique to the direction of the current, or they grew in two or 
more planes at various angles with one another. In other words, 
the velocities below 2°" per minute ceased to control the direction of 
: The fact last. mentioned is further emphasized by the 
behavior of the roots of Brassica alba in basins of water revolv- 
> ing once in 24 minutes. With such a speed as this, the velocity 
in the outer channel of the basin extends from 2. 50™ to 1.80™ 
_ Pet minute, and in the inner channel from 1. 50™ to 0.78% 
_ Per minute. The behavior of the roots was about the same in 
both channels. Seventy- -eight roots were used, the temperature 
maintained constantly at 22° in air, and the period being — 
9 oars, 15 hours, 24 hours, and 28 hours in four experiments. 
s Twenty-two roots inclined against the stream, fifteen with the 
: Raed forty-one roots were neutral. This gives 28 per — , : 
i a. 19 per cent. negative, and 53 per cent. neutral. — 
be unfair to regard these proportions as of much me 
rt ghather should it be said that the lower limit oF 
‘ €cting positive responses on the part of these roots — 
a It cannot be said, however, that the stream — 
ut influence on the direction of growth. Two- 
- devig _* . mustard roots in velocities below 2™ per minute | 
“= of oul the vertical direction in their growth. For pur- : 
o ‘ummarizing the results above, all roots bent 
given re 
oa ‘Plane in which the seedlings were oe 
