rapidity down the pedicel of the same tentacle to the basal part which
alone bends. The impulse, then passing onwards, spreads on all sides to
the surrounding tentacles, first affecting those which stand nearest
and then those farther off. But by being thus spread out, and from the
cells of the disc not being so much elongated as those of the
tentacles, it loses force, and here travels much more slowly than down
the pedicels. Owing also to the direction and form of the cells, it
passes with greater ease and celerity in a longitudinal than in a
transverse line across the disc. The impulse proceeding from the glands
of the extreme marginal tentacles does not seem to have force enough to
affect the adjoining tentacles; and this may be in part due to their
length. The impulse from the glands of the next few inner rows spreads
chiefly to the tentacles on each side and towards the centre of the
leaf; but that proceeding from the glands of the shorter tentacles on
the disc radiates almost equally on all sides.
When a gland is strongly excited by the quantity or quality of the
substance placed on it, the motor impulse travels farther than from one
slightly excited; and if several glands are simultaneously excited, the
impulses from all unite and spread still farther. As soon as a gland is
excited, it discharges an impulse which extends to a considerable
distance; but afterwards, whilst the gland is secreting and absorbing,
the impulse suffices only to keep the same tentacle [page 276]
inflected; though the inflection may last for many days.
If the bending place of a tentacle receives an impulse from its own
gland, the movement is always towards the centre of the leaf; and so it
is with all the tentacles, when their glands are excited by immersion
in a proper fluid. The short ones in the middle part of the disc must
be excepted, as these do not bend at all when thus excited. On the
other hand, when the motor impulse comes from one side of the disc, the
surrounding tentacles, including the short ones in the middle of the
disc, all bend with precision towards the point of excitement, wherever
this may be seated. This is in every way a remarkable phenomenon; for
the leaf falsely appears as if endowed with the senses of an animal. It
is all the more remarkable, as when the motor impulse strikes the base
of a tentacle obliquely with respect to its flattened surface, the
contraction of the cells must be confined to one, two, or a very few
rows at one end. And different sides of the surrounding tentacles must
be acted on, in order that all should bend with precision to the point
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