278 BOTANICAL GAZETTE [APRIL 
of these straightened. Raphanus sativus, during the first three 
hours of an experiment in which twelve seedlings were placed 
with their roots dipping into water, the velocities at the various — 
distances from the center of the basin ranging from 50™ to 100 
per minute, and the water temperature being 22°, gave rheotropic 
responses in the three outermost roots. These roots after the 
lapse of four hours were seen to be straightening. Within the 
first seven hours of the experiment seven of the twelve roots 
bent positively, but after seven hours more, all twelve roots, 
except two tardily straightening ones, were in the vertical position, 
except for the fixed portions of the rheotropic curves. oe 
Analyzing these results, it would seem that the matter canbe : 
thus stated: (1) a rheotropic curve in response to @ weak : 
stimulus will, sooner or later, be overcome by the response, 
gravitation, so that only the geotropic response is evident ; (2) 
a stronger rheotropic stimulus acting at the same time with 9 
normal yeotropic stimulus may produce a curve giving a deviation 
of less than go° from the vertical, this direction being tga" 
asa resultant of the water current stimulus and the gan 
stimulus ; (3) with highly sensitive roots anda suit ee 
‘stimulus, an angle of go° from the vertical may be attained, ie 
that the geotropic response of the plant is wholly ony 
the rheotropic, except for the geotropic counter-cur pases oe 
_be discussed later. 
_ The overcoming of the response to one st 
_ another is well illustrated also in the horizontal 
by stems in response to horizontally directed rays 0 
. heliotropism apparently vanquishes geotropism. 
imulus by that a 
position take 
f light, where 
oe -—s—sSY. «OTHE GEOTROPIC COUNTER-CURVE- 
oo One who studies the rheotropic behavior of 
thus forming with the ve ee ; 
the root farther back. If, for example, there oe a 
> of 60°, the apex of the root will often oe 
