could not have been overlooked, as I made thin vertical sections of the
leaf at the bases of the filaments.
On several occasions, slits about the 1/10 of an inch in length were
made with a lancet, close to the bases of the filaments, parallel to
the midrib, and, therefore, directly across the course of the vessels.
These were made sometimes on the inner and sometimes on the outer sides
of the filaments; and after several days, when the leaves had reopened,
these filaments were touched roughly (for they were always rendered in
some degree torpid by the operation), and the lobes then closed in the
ordinary manner, though slowly, and sometimes not until after a
considerable interval of time. These cases show that the motor impulse
is not transmitted along the vessels, and they further show that there
is no necessity for a direct line of communication from the filament
which is [page 315] touched towards the midrib and opposite lobe, or
towards the outer parts of the same lobe.
Two slits near each other, both parallel to the midrib, were next made
in the same manner as before, one on each side of the base of a
filament, on five distinct leaves, so that a little slip bearing a
filament was connected with the rest of the leaf only at its two ends.
These slips were nearly of the same size; one was carefully measured;
it was .12 of an inch (3.048 mm.) in length, and .08 of an inch (2.032
mm.) in breadth; and in the middle stood the filament. Only one of
these slips withered and perished. After the leaf had recovered from
the operation, though the slits were still open, the filaments thus
circumstanced were roughly touched, and both lobes, or one alone,
slowly closed. In two instances touching the filament produced no
effect; but when the point of a needle was driven into the slip at the
base of the filament, the lobes slowly closed. Now in these cases the
impulse must have proceeded along the slip in a line parallel to the
midrib, and then have radiated forth, either from both ends or from one
end alone of the slip, over the whole surface of the two lobes.
Again, two parallel slits, like the former ones, were made, one on each
side of the base of a filament, at right angles to the midrib. After
the leaves (two in number) had recovered, the filaments were roughly
touched, and the lobes slowly closed; and here the impulse must have
travelled for a short distance in a line at right angles to the midrib,
and then have radiated forth on all sides over both lobes. These
275