442 Newcombe.— The Sensory Zone of Roots. 
limit of elongation for most individuals of this variety. At 
the distance of 20 mm. from the apex, the sensitiveness of the 
roots is so great as to bring approximately the same per- 
centage of curves as is produced when the whole root is 
subjected to the water-stream. It is probable, though not 
certain, that the roots are sensitive 25 mm. from the apex. 
In the effort to extend the study of the phenomena here 
treated over as wide a range as possible, an attempt was 
made to add a representative of the Leguminosae to the 
number of those included in the experiments. So far as 
tested, only two species of this family could be thought of 
with any hope of success, these two being Pisum sativum , L., 
and Vicia sativa , L. In my tests \ I had found Pisum some- 
what more sensitive than Vicia. Both plants give a rather 
high proportion of crooked roots in water, and both have 
been shown to respond rather slowly to a rheotropic stimulus. 
Individual roots in both species, when the whole root received 
the stimulus 2 , have been seen to respond within two hours 
after the application of the stimulus, but the majority of roots 
in both species show no curves till after the lapse of six to 
eight hours. 
Pisum sativtim was selected for experiment, and over one 
hundred seedlings tested by shielding various lengths of root 
from the water-stream. The roots curved, but in all direc- 
tions, and the curves were evidently due to the objectionable 
environment of water, and not to the water-stream. A 
control was set up in still water, without using the glass-tubes, 
and the curves came in the same way. Ten seedlings with 
naked roots were tested for rheotropism, but gave no rheo- 
tropic curves, only distortion curves, during twelve hours. 
The attempt to use this plant with the glass-tubes was 
thereupon abandoned. 
1 Newcombe, Bot. Gazette, xxxiii, 1902, p. 177. 
2 Juel, Untersuchungen iiber den Rheotropismus der Wurzeln. Jahrb. f. wiss. 
Botanik, xxxiv, p. 507. Newcombe, loc. cit. 
