New combe, — The Sensory Zone of Roots . 435 
the water-stream by glass-tubes. Temperature of the water 
= 23° to 2 4 0 ; duration of experiments = from 9 to 12 hours; 
velocities — from 200 cm. to 700 cm. per minute. 
No. 
Seedlings. 
Extent of 
Apex shielded. 
Positive Curves. 
Neutral Roots. 
Negative Curves. 
48 
10 mm. 
34 = 7i% 
1 1 
3 
50 
15 mm. 
28 = 56% 
18 
4 
33 
20 mm. 
H = 42% 
14 
4 
The results recorded in this table would seem to show that 
the root of Raphanus sativus is sensitive to the water-stream 
at least 20 mm. back from the apex. It is true that the 
number of positive responses is not large, but it is large 
enough to indicate clearly that some directive influence was 
at work, especially as there were but four negative curves. 
The roots of Raphanus do not distort in water, nor do they 
nutate through any considerable angle. The angles attained 
in all the curves counted as rheotropic were never below io°, 
and were often 30° to 45 0 . A majority were above 15 0 . 
The foregoing table also shows that the sensitiveness of 
the roots decreases with the distance from the elongating 
zone, though, when the stimulus is applied 10 mm. from the 
apex, nearly as many positive curves appear as when the 
whole root is exposed to the water-stream. My former 
paper 1 shows that this plant, when the whole root receives 
the stimulus, gives 87 per cent, of positive responses ; when 
the apex to a distance of 10 mm. is shielded, positive curves 
equal to 71 per cent, appear. 
A second plant whose irritability back of the elongating 
zone was tested is Brassica alba , Boiss. This plant was 
known to be highly sensitive to the action of a stream of 
water 1 , and for this reason was selected for experiment. The 
preparation was made and the experiments carried out in 
the same way as for Raphanus , the plants being shielded 
1 Newcombe, Bot. Gazette, xxxiii, 1902, p. 177. 
H h 
