action, in the same manner as when a sensory nerve is irritated, and
carries an impression to a ganglion which sends back some influence to
a muscle or gland, causing movement or increased secretion; but the
action in the two cases is probably of a widely different nature. After
the protoplasm in a tentacle has been aggregated, its redissolution
always begins in the lower part, and slowly travels up the pedicel to
the gland, so that the protoplasm last aggregated is first redissolved.
This probably depends merely on the protoplasm being less and less
aggregated, lower and lower down in the tentacles, as can be seen
plainly when the excitement has been slight. As soon, therefore, as the
aggregating action altogether ceases, redissolution naturally commences
in the less strongly aggregated matter in the lowest part of the
tentacle, and is there first completed.
Direction of the Inflected Tentacles. When a particle of any kind is
placed on the gland of one of the outer tentacles, this invariably
moves towards the centre of the leaf; and so it is with all the
tentacles of a leaf immersed in any exciting fluid. The glands of the
exterior tentacles then form a ring round the middle part of the disc,
as shown in a previous figure (fig. 4, [page 244] p. 10). The short
tentacles within this ring still retain their vertical position, as
they likewise do when a large object is placed on their glands, or when
an insect is caught by them. In this latter case we can see that the
inflection of the short central tentacles would be useless, as their
glands are already in contact with their prey.
FIG. 10. (Drosera rotundifolia.) Leaf (enlarged) with the tentacles
inflected over a bit of meat placed on one side of the disc.
The result is very different when a single gland on one side of the
disc is excited, or a few in a group. These send an impulse to the
surrounding tentacles, which do not now bend towards the centre of the
leaf, but to the point of excitement. We owe this capital observation
to Nitschke,* and since reading his paper a few years ago, I have
repeatedly verified it. If a minute bit of meat be placed by the aid of
a needle on a single gland, or on three or four together, halfway
between the centre and the circumference of the disc, the directed
movement of the surrounding tentacles is well exhibited. An accurate
drawing of a leaf with meat in this position is here reproduced (fig.
10), and we see the tentacles, including some of the exterior ones,
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