t of the sensitive
cotyledon is intact. In view of this result it was impossible to rely on
the amputations performed on roots as above described.

At this juncture a new and brilliant method originated in Pfeffer's
laboratory. (See Pfeffer, "Annals of Botany", VIII. 1894, page 317, and
Czapek, Pringsheim's "Jahrb." XXVII. 1895, page 243.) Pfeffer and Czapek
showed that it is possible to bend the root of a lupine so that, for
instance, the supposed sense-organ at the tip is vertical while the
motile region is horizontal. If the motile region is directly sensitive
to gravity the root ought to curve downwards, but this did not occur: on
the contrary it continued to grow horizontally. This is precisely what
should happen if Darwin's theory is the right one: for if the tip is
kept vertical, the sense-organ is in its normal position and receives no
stimulus from gravitation, and therefore can obviously transmit none to
the region of curvature. Unfortunately this method did not convince the
botanical world because some of those who repeated Czapek's experiment
failed to get his results.

Czapek ("Berichte d. Deutsch. bot. Ges." XV. 1897, page 516, and
numerous subsequent papers. English readers should consult Czapek in the
"Annals of Botany", XIX. 1905, page 75.) has devised another interesting
method which throws light on the problem. He shows that roots, which
have been placed in a horizontal position and have therefore been
geotropically stimulated, can be distinguished by a chemical test from
vertical, i.e. unstimulated roots. The chemical change in the root can
be detected before any curvature has occurred and must therefore be a
symptom of stimulation, not of movement. It is particularly interesting
to find that the change in the root, on which Czapek's test depends,
takes place in the tip, i.e. in the region which Darwin held to be the
centre for gravitational sensitiveness.

In 1899 I devised a method (F. Darwin, "Annals of Botany", XIII. 1899,
page 567.) by which I sought to prove that the cotyledon of Setaria is
not only the organ for light-perception, but also for gravitation. If
a seedling is supported horizontally by pushing the apical part
(cotyledon) into a horizontal tube, the cotyledon will, according to
my supposition, be stimulated gravitationally and a stimulus will be
transmitted to the basal part of the stem (hypocotyl) causing it to
bend. But this curvature merely raises the basal end of the seedling,