accurately directed to the point where the meat lay. But a much better
* Bot. Zeitung, 1860, p. 240. [page 245]
plan is to place a particle of the phosphate of lime moistened with
saliva on a single gland on one side of the disc of a large leaf, and
another particle on a single gland on the opposite side. In four such
trials the excitement was not sufficient to affect the outer tentacles,
but all those near the two points were directed to them, so that two
wheels were formed on the disc of the same leaf; the pedicels of the
tentacles forming the spokes, and the glands united in a mass over the
phosphate representing the axles. The precision with which each
tentacle pointed to the particle was wonderful; so that in some cases I
could detect no deviation from perfect accuracy. Thus, although the
short tentacles in the middle of the disc do not bend when their glands
are excited in a direct manner, yet if they receive a motor impulse
from a point on one side, they direct themselves to the point equally
well with the tentacles on the borders of the disc.
In these experiments, some of the short tentacles on the disc, which
would have been directed to the centre, had the leaf been immersed in
an exciting fluid, were now inflected in an exactly opposite direction,
viz. towards the circumference. These tentacles, therefore, had
deviated as much as 180o from the direction which they would have
assumed if their own glands had been stimulated, and which may be
considered as the normal one. Between this, the greatest possible and
no deviation from the normal direction, every degree could be observed
in the tentacles on these several leaves. Notwithstanding the precision
with which the tentacles generally were directed, those near the
circumference of one leaf were not accurately directed towards some
phosphate of lime at a rather distant point on the opposite side of the
disc. It appeared as if the motor [page 246] impulse in passing
transversely across nearly the whole width of the disc had departed
somewhat from a true course. This accords with what we have already
seen of the impulse travelling less readily in a transverse than in a
longitudinal direction. In some other cases, the exterior tentacles did
not seem capable of such accurate movement as the shorter and more
central ones.
222