hair, 1/50 of an inch in length, and therefore much larger than those
used in the above experiments, was not perceived when placed on my
tongue; and it is extremely doubtful whether any nerve in the human
body, even if in an inflamed condition, would be in any way affected by
such a particle supported in a dense fluid, and slowly brought into
contact with the nerve. Yet the cells of the glands of Drosera are thus
excited to transmit a motor impulse to a distant point, inducing
movement. It appears to me that hardly any more remarkable fact than
this has been observed in the vegetable kingdom. [page 34]
The Inflection of the Exterior Tentacles, when their Glands are excited
by Repeated Touches.
We have already seen that, if the central glands are excited by being
gently brushed, they transmit a motor impulse to the exterior
tentacles, causing them to bend; and we have now to consider the
effects which follow from the glands of the exterior tentacles being
themselves touched. On several occasions, a large number of glands were
touched only once with a needle or fine brush, hard enough to bend the
whole flexible tentacle; and though this must have caused a
thousand-fold greater pressure than the weight of the above described
particles, not a tentacle moved. On another occasion forty-five glands
on eleven leaves were touched once, twice, or even thrice, with a
needle or stiff bristle. This was done as quickly as possible, but with
force sufficient to bend the tentacles; yet only six of them became
inflected, three plainly, and three in a slight degree. In order to
ascertain whether these tentacles which were not affected were in an
efficient state, bits of meat were placed on ten of them, and they all
soon became greatly incurved. On the other hand, when a large number of
glands were struck four, five, or six times with the same force as
before, a needle or sharp splinter of glass being used, a much larger
proportion of tentacles became inflected; but the result was so
uncertain as to seem capricious. For instance, I struck in the above
manner three glands, which happened to be extremely sensitive, and all
three were inflected almost as quickly, as if bits of meat had been
placed on them. On another occasion I gave a single for- [page 35]
cible touch to a considerable number of glands, and not one moved; but
these same glands, after an interval of some hours, being touched four
or five times with a needle, several of the tentacles soon became
inflected.
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