The Localisation of Perception. 
37 
67-4 : 100. It is therefore certain that the loss of geotropic capacity 
in the decapitated roots was not due to diminished growth-rate. 
In stating my conclusions ( loc. cit., p. 229), I pointed out that 
“ geotropism, though accompanied and carried into effect by growth, 
cannot be treated as a mere distribution of growth of different 
intensities on the upper and lower halves of the root. But it must 
be looked at as qualitatively different from longitudinal growth, 
and dependent on different conditions for its completion.” I went 
on to point out that the effect of amputation, (?'.<?., the loss of geo¬ 
tropic curvature), may either be due to the removal of the root- 
tip in which the act of geoperception is conceived to occur; or we 
may suppose that injuring the tip of the root “has a special 
paralysing effect on the power which roots possess of receiving the 
stimulus of gravitation.” This is the alternative which must be faced. 
Does amputation act by removing a sense-organ ? or by shock ? 
In the case of heliotropism it has been proved 1 that the removal 
of a small part of the photo-perceptive region prevents heliotropism, 
and here since the whole of the sense organ is not removed the 
result must be due to shock. This is a most important result, for 
it is impossible to deny that what is true of heliotropism may apply 
to geotropism, and therefore the argument derived from decapitation 
experiments on roots falls to the ground; because we can never 
separate the loss of the sense organ as such from the possible 
effect of shock. The attempt to distinguish between the motor 
and sensory regions in the root seemed therefore to be a hopeless 
one, when Czapek’s brilliant researches was made known. 2 The 
method is well known and consists in inducing curvature at the 
extreme tip of the root by allowing it to grow into a little glass 
boot. Under these circumstances the supposed sense organ for 
gravitation is at right angles to the motor region, so that if the 
motor region is horizontal and the tip points vertically downwards 
no curvature should occur since the sense organ is in the position 
of equilibrium. This is what Czapek found to occur, and he 
further showed that in whatever position the root is placed it 
executes the curvature needed to bring the tip into the vertical, 
and when this is affected curvature ceases. Czapek’s results have 
1 Rothert’s Cohn’s Beitrage, VII. Those who are interested in 
the subject should read Rothert’s admirable essay in Flora, 
1894 (Ergiinzungs Bd.), whence the argument from helio¬ 
tropism is taken. 
2 Pfeffer, Annals of Botany, 1894. Czapek, Pringsheim’s Jahrb. 
XXVII., 1895. 
