a dozen to a dozen tentacles, both laterally and towards
the centre, were well inflected or sub-inflected.
Lastly, in [page 236] ten other experiments, minute
bits of meat were placed on a single gland or on two
glands in the centre of the disc. In order that
no other glands should touch the meat, through the
inflection of the closely adjoining short tentacles,
about half a dozen glands had been previously removed
round the selected ones. On eight of these leaves
from sixteen to twenty-five of the short surrounding
tentacles were inflected in the course of one or two
days; so that the motor impulse radiating from one
or two of the discal glands is able to produce this
much effect. The tentacles which had been removed
are included in the above numbers; for, from standing
so close, they would certainly have been affected.
On the two remaining leaves, almost all the short
tentacles on the disc were inflected. With a
more powerful stimulus than meat, namely a little phosphate
of lime moistened with saliva, I have seen the inflection
spread still farther from a single gland thus treated;
but even in this case the three or four outer rows
of tentacles were not affected. From these experiments
it appears that the impulse from a single gland on
the disc acts on a greater number of tentacles than
that from a gland of one of the exterior elongated
tentacles; and this probably follows, at least in
part, from the impulse having to travel a very short
distance down the pedicels of the central tentacles,
so that it is able to spread to a considerable distance
all round.
Whilst examining these leaves, I was struck with the
fact that in six, perhaps seven, of them the tentacles
were much more inflected at the distal and proximal
ends of the leaf (i.e. towards the apex and base)
than on either side; and yet the tentacles on the sides
stood as near to the gland where the bit of meat lay
as did those at the two ends. It thus appeared
as [page 237] if the motor impulse was transmitted
from the centre across the disc more readily in a
longitudinal than in a transverse direction; and as
this appeared a new and interesting fact in the physiology
of plants, thirty-five fresh experiments were made
to test its truth. Minute bits of meat were placed
on a single gland or on a few glands, on the right
or left side of the discs of eighteen leaves; other
bits of the same size being placed on the distal or
proximal ends of seventeen other leaves. Now if
the motor impulse were transmitted with equal force
or at an equal rate through the blade in all directions,
a bit of meat placed at one side or at one end of the
disc ought to affect equally all the tentacles situated
at an equal distance from it; but this certainly is
not the case. Before giving the general results,
it may be well to describe three or four rather unusual
cases.