568 Darwin. — On Geotropism and the 
amputation. The result was that the roots so treated lost 
nearly or completely their power of curving geotropically. 
The conclusion drawn from this experiment, namely, that 
the root-tip is a sense-organ for gravitation, was much 
criticized, sometimes unjustly, but in one respect with justice. 
It was said that amputation might act as a shock and thus 
prevent curvature. It was this — the difficulty of distinguish- 
ing between the removal of the sense-organ, and the dis- 
turbing effect of the operation of removal — that made Rothert 1 
(in his admirable summary of the question) despair of any 
solution. However, in August, 1894, Pfefifer 2 read a paper 
at the Oxford meeting of the British Association, in which 
he explained his well-known method, now generally associated 
with the name of his brilliant pupil Czapek 3 . The root is 
forced to grow into a little glass stocking, that is to say, 
a tube closed at one end and bent at right angles, so that 
while that part of the root which is capable of curvature 
is horizontal the tip is vertical. Under these circumstances 
no fresh curvature takes place ; the sense-organ at the tip 
of the root is not stimulated, since it points vertically down- 
wards : it is, as it were, satisfied with its position, and 
consequently transmits no influence to the bending region. 
This beautiful method has not been found applicable to other 
organs, and thus it happens that apogeotropic sensitiveness 4 
has not been localized as far as I know. Rothert 5 and 
Czapek 6 have indeed shown some reason to believe that in 
the case of Arena and Phalaris the tip is the percipient part ; 
but neither method is, in my opinion, absolutely convincing. 
1 Flora, 1894, vol. lxxix. 
2 Annals of Botany, Sept. 1894, p. 317. 
3 Czapek, Prings. Jahrb., 1895, p. 243. 
4 In the case of diageotropic flowers, where the part which is horizontal takes 
no part in the curvature, there must be transmission of stimulus, as Vochting 
(Bewegungen d. Bliithen und Friichte) and Schwendener and Krabbe (Abhand. d. 
k. Preuss. Akad., Berlin, 1892) have shown. Czapek (Pringsheim’s Jahrb., xxxii, 
1898, p. 274) shows that diageotropic sensibility is to a great extent localized 
in the lamina of a Tropaeolum leaf. 
5 Cohn’s Beitrage, Bd. vii, Heft 1, 1894, p. 187 of reprint. 
6 Pringsheim’s Jahrb., 1898, p. 254. 
