Inflection of the exterior tentacles owing to the glands of the disc
being excited by repeated touches, or by objects left in contact with
them--Difference in the action of bodies yielding and not yielding
soluble nitrogenous matter--Inflection of the exterior tentacles
directly caused by objects left in contact with their glands--Periods
of commencing inflection and of subsequent re-expansion--Extreme
minuteness of the particles causing inflection--Action under
water--Inflection of the exterior tentacles when their glands are
excited by repeated touches--Falling drops of water do not cause
inflection.

I WILL give in this and the following chapters some of the many
experiments made, which best illustrate the manner and rate of movement
of the tentacles, when excited in various ways. The glands alone in all
ordinary cases are susceptible to excitement. When excited, they do not
themselves move or change form, but transmit a motor impulse to the
bending part of their own and adjoining tentacles, and are thus carried
towards the centre of the leaf. Strictly speaking, the glands ought to
be called irritable, as the term sensitive generally implies
consciousness; but no one supposes that the Sensitive-plant is
conscious, and as I have found the term convenient, I shall use it
without scruple. I will commence with the movements of the exterior
tentacles, when indirectly excited by stimulants applied to the glands
of the short tentacles on the disc. The exterior tentacles may be said
in this case to be indirectly excited, because their own glands are not
directly acted on. The stimulus proceeding from the glands of the disc
acts on the bending part of the [page 20] exterior tentacles, near
their bases, and does not (as will hereafter be proved) first travel up
the pedicels to the glands, to be then reflected back to the bending
place. Nevertheless, some influence does travel up to the glands,