Newcombe, Gravitation sensitiveness not confined to apex of root. QQ 
sition when responding- rheotropically to a stream of water, con- 
tinue on in tlie same direction for days after the flow of wafer 
had ceased, producing a form like Fig. 4. 
It is not unusual to find individual seedlings of Vicia faha 
and Lu'pinus albus when snspended horizontally in a damp cham- 
ber hending 2 or 3 mm of the tip obliquely down ward, but 
straightening again in the elongating zone so that ihe course of 
the root continues horizontal or between the horizontal and the 
vertically downward position, thus ])roducing a form quite similar 
to Czapek’s preparation as shown in Fig. 3. Czapek obtained 
the straightening of bent roots by revolving the bent roots on the 
klinostat. But the cases just cited show that the straightening 
will often occur when the full Stimulus of gravitation is applied to 
a horizontal root at rest. It is evident therefore that the ten- 
dency of a root to respond geotropically is opposed by 
its own autotropism. In the case of Vicia faha and Lu'pinus 
albus the autotropism of a horizontally lying’ root is sometimes 
able to prevent a complete response to gravitätion. 
Instead of ascribing, as Czapek does, the continued horizon¬ 
tal growth of a root, in the form shown in Fig. 3, to the absence 
of geotropic sensitiveness in the part posterior to the 2 mm of 
the apex, is it not just as reasonable to ascribe the straightening 
to autotropism combined with a greater sensitiveness to gravitation 
in the apex than in the straightening part? 
If we assume that the apical 2 mm are much more sensi¬ 
tive to gravitation than the part behind, then the root shown in 
Fig. 1 must bend into the form of Fig. 2; and the seedling shown 
in Fig. 3 cannot bend its post-apical part downward, for in so 
doing it would throw its apex out of the vertical, out of the Po¬ 
sition of equilibrium. 
Thus it is seen that Czapek’s experiment with the glass-caps 
has not and cannot prove the absence of geotropic sensitiveness 
in the part of the root posterior to the apical one or two milli- 
meters. 
The argument against the methods and conclusions of Czapek 
applies with just as much force to those in his second paper^) 
and to those recently published by F. Darwin^), Massart^), An¬ 
drews^) and Cholodnyjö). 
Thus there is presented here an hypothesis which will account 
for the results obtained by Cz apek, and which implies the possession 
q über den Nachweis der geotropischen Sensibilität der Wurzelspitze. 
(Jahrb. wiss. Botanik. XXXV. 1900. 313.) 
On a method of investigating the gravitational sensitiveness of the 
root-tip. (Journ. Linn. Soc. XXXV. 1902. 266.) . 
^) Sur l’irritabilite des plantes superieures. (Mem. couron. par l’Acad. 
de Belgique. Bruxelles. 1902. — Review in Bot. Zeit. 61. 1903. Abt. II. 23.) 
^) A natural proof that the root-tip alone is sensitive to the gravitation 
Stimulus. (Proc. Indiana Acad. Sei. 1905. 189.) 
®) Zur Frage über die Verteilung der geotropischen Sensibilität in der 
Wurzel. (Schriften des Naturforschervereins in Kiew. 1906.— Review in Bot 
Zeit. 65. 1907. Abt. II. 189.) 
y * 
