43 8 New combe. — The Sensory Zone of Roots. 
Compared with the tables for Raphanus and Brassica , this 
one for Fagopyrum shows a proportionally much larger 
number of negative curves and a smaller number of neutral 
roots, indicating that we cannot for Fagopyrum reckon all the 
positive curves as due to the water-stream. If we subtract 
from the positive curves in each group, the number of negative 
curves in the same group, we ought to obtain approximately 
the true number of rheotropic responses. This statement, of 
course, assumes that there is no such response as negative 
rheotropism, a belief in which I have been confirmed by all 
my work on rheotropism. 
The individual experiments in the group with io mm. of 
the root covered, and also those with 15 mm. covered, are 
uniform in showing in all cases a majority of all roots with 
positive curves. The five experiments in the group with 
20 mm. of the apex covered varied considerably in the results 
shown, three having a majority of positive curves, one a 
majority of negative curves, and two having an equal number 
of positive and negative curves. The apparent tendency 
toward positive curving is here so slight that no claim can be 
made for sensitiveness at a distance of 20 mm. from the 
apex. 
The explanation of the relatively much larger number of 
negative roots when 20 mm. of the apex are covered than 
when 10 mm. or 15 mm. are covered, is found probably in 
the weaker effect of the stimulus of the water-stream when 
applied at 20 mm. from the apex. As a result of the lesser 
effect of this stimulus, the direction of growth of the root 
is left more under the control of the stimulus which leads 
to distorted growth. It has been shown elsewhere 1 that, in 
rheotropic experiments with the naked roots of this plant 
in water, the initial distortion curves are converted into 
positive rheotropic curves, or rather that the various directions 
taken initially, due to distortion, are later brought into a 
common direction which is parallel with the current of the 
water. 
1 Newcombe, Bot. Gazette, xxxiii, 1902, p. 177* 
