New combe. — The Sensory Zone of Roots. 445 
is, however, out of any possibility that so many tubes should 
have been inclined in a direction favourable to a downward 
flow of a stream, and that, owing to this flow, so many roots 
should have been bent in a constant direction as to give the 
percentages of responses shown in the tables. (3) To guard 
against the possibility of a flow of water in the tubes, several 
experiments were carried through in which the lower ends 
of the tubes were closed by a firm plug of cotton. In these 
cases the curves came just as promptly and as numerously as 
when the tubes were left open. 
There was no possibility of mistaking geotropic or helio- 
tropic curves for rheotropic ; for, as stated elsewhere, during 
the preparation the seedlings were kept in the vertical direc- 
tion, and all the experiments were carried on in the dark-room. 
Moreover, the preparations often stood at rest for hours after 
setting up before the revolution of the basins of water was 
begun, thus affording time for overcoming the effect of any 
preceding geotropic or heliotropic stimulus. Besides all this, 
the initial bends in my experiments never came in less than 
two hours, and, in the majority of roots, not till five or more 
hours after the beginning of the revolution. Such a latent 
period as this is not at all unusual for rheotropism, as shown 
by the work of Berg 1 , Juel 2 , and myself 3 . 
It might be thought that the contact of the root with the 
glass-tube would cause a curvature. To this it may be said 
that no response to contact has been demonstrated for roots. 
Moreover, experiments set up to test the effect of contact be- 
tween roots and glass-tubes have shown no curves resulting. 
From all the considerations presented in the foregoing 
pages, the rheotropic sensitiveness of the root at a considerable 
distance from the limit of the elongating zone may, I believe, 
be accepted as demonstrated. Juel 4 had obtained curves in 
two roots of Vida sativa covered with collodion caps for 
a distance of 7 to 8 mm. from the apex. This number was 
1 Berg, Studien iiber Rheotropismus. Lunds Univ. Arsskrift, xxxv, II, No. 6. - 
3 Juel, Jahrb. f. wiss. Botanik, xxxiv, 507. 
8 Neweombe, Bot. Gazette, xxxiii, 1902, p. 177. 4 Juel, loc. cit., p. 519. 
