Newcombe . — The Sensory Zone of Roots. 437 
These curves varied between io° and 90°, the most of them 
being between 15 0 and 30°. 
To determine the extent of the elongating zone of Brassica 
alba, the roots of four plants were marked with India ink, and 
immediately measured with a horizontal microscope. Subse- 
quent examination showed that three of these plants had 
elongated only in the first 5 mm., while the fourth had made 
a slight growth in the sixth millimetre also. These roots 
were kept in water both before and after the preparation for 
measurement. 
Fagopyrum esculentum , Moench., when its naked roots are 
immersed in flowing water of suitable velocity 1 , has shown 
a positive response in 92 per cent, of the total number of roots 
used. It is therefore highly sensitive rheotropically. But 
unlike Raphanus sativus and Brassica alba , it has the dis- 
advantage of growing with a considerable number of contor- 
tions in water. It has been selected for experiment in the 
study of the extent of the sensitive area in roots, but it gives, 
as one would expect, a larger number of negative bends, 
these negative bends being considered not as rheotropic 
responses, but rather as the result of the objectional environ- 
ment of water, whatever that may be. The tabular summary 
of the behaviour of F agopyrum, when treated as the two 
preceding plants were, appears as follows : — - 
Table III. Fagopyrum esculenUtm with root-tips shielded 
from water-stream by glass-tubes. T emperature of the water 
= 23° to 24 0 ; duration of experiments = 10 to 11 hours; 
velocities = from 200 to 700 cm. per minute. 
No. 
Seedlings. 
Extent of 
Apex shielded. 
Positive Curves. 
Neutral Roots. 
Negative Curves. 
38 
10 mm. 
29 = 76% 
3 
6 
4i 
15 mm. 
24 = 59% 
10 
7 
36 
20 mm. 
17 = 47% 
5 
14 
5 
25 mm. 
0 
II 
0 
4 
1 
1 Newcombe, Bot. Gazette, xxxiii, 1902, p. 177. 
H h 2 
