That a plant and an animal should secrete the same, or nearly the same,
complex digestive fluid, adapted for a similar purpose, is a wonderful
fact in physiology, but not more remarkable than the movements of a
tentacle consequent upon an impulse received from its own gland, the
movement at the bending place of the tentacle being always towards
the centre of the leaf, and so it is with all the tentacles when
their glands are excited by immersion in a suitable fluid. The short
tentacles in the middle part of the disc, however, must be excepted,
as these do not bend at all when thus excited. But when the motor
impulse comes from one side of the disc, the surrounding tentacles,
and even the short ones in the middle of the disc, all bend with
precision towards the point of excitement, no matter where it may be
located. This is in every way a remarkable phenomenon, for the leaf
appears as if endowed with animal sense and intelligence. It is all the
more remarkable when the motor impulse strikes the base of a tentacle
obliquely to its flattened surface, for then the contraction of the
cells must be restricted to one, two or a very few rows at one end, and
different sides of the surrounding tentacles must be acted on that all
may bend with precision to the point of excitement. The motor impulse,
as it spreads from one or more glands across the disc, enters the bases
of the surrounding tentacles, and instantly acts on the bending place,
but does not first proceed up the tentacles to the glands, causing them
to reflect back an impulse to their bases, although some influence
is sent up to the glands, whereby their secretion is soon increased
and rendered acid. The glands, being thus excited, send back some
other influence, dependent neither on increased secretion nor on the
inflection of the tentacles, which causes the protoplasm to aggregate
in cell beneath cell. This maybe called a reflex action. How it differs
from that which proceeds from the nerve-ganglion of an animal, if it
differ at all, no one can say. It is probably the only known case of
reflex action in the vegetable kingdom.
Public-domain text, read in full here on John Shaqi.
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