Insectivorous Plants | Page 6

be
described, the papillae, which project from the upper surface of the leaf
and of the tentacles, probably absorb some of the animal matter
dissolved in the secretion; but this cannot be the case with the papillae
on the backs of the leaves or on the petioles.]
* Nitschke has elaborately described and figured these papillae, 'Bot.
Zeitung,' 1861, pp. 234, 253, 254. [page 9]
Preliminary Sketch of the Action of the several Parts, and of the
Manner in which Insects are Captured.
If a small organic or inorganic object be placed on the glands in the
centre of a leaf, these transmit a motor impulse to the marginal
tentacles. The nearer ones are first affected and slowly bend towards
the centre, and then those farther off, until at last all become closely
inflected over the object. This takes place in from one hour to four or
five or more hours. The difference in the time required depends on
many circumstances; namely on the size of the object and on its nature,
that is, whether it contains soluble matter of the proper kind; on the
vigour and age of the leaf; whether it has lately been in action; and,
according to Nitschke,* on the temperature of the day, as likewise
seemed to me to be the case. A living insect is a more efficient object
than a dead one, as in struggling it presses against the glands of many
tentacles. An insect, such as a fly, with thin integuments, through
which animal matter in solution can readily pass into the surrounding
dense secretion, is more efficient in causing prolonged inflection than
an insect with a thick coat, such as a beetle. The inflection of the
tentacles takes place indifferently in the light and darkness; and the
plant is not subject to any nocturnal movement of so-called sleep.
If the glands on the disc are repeatedly touched or brushed, although no
object is left on them, the marginal tentacles curve inwards. So again, if

drops of various fluids, for instance of saliva or of a solution of any salt
of ammonia, are placed on the central glands, the same result quickly
follows, sometimes in under half an hour.
* 'Bot. Zeitung,' 1860, p. 246. [page 10]
The tentacles in the act of inflection sweep through a wide space; thus a
marginal tentacle, extended in the same plane with the blade, moves
through an angle of 180o; and I have seen the much reflected tentacles
of a leaf which stood upright move through an angle of not less than
270o. The bending part is almost confined to a short space near the
base; but a rather larger portion of the elongated exterior tentacles
FIG. 4. (Drosera rotundifolia.) Leaf (enlarged) with all the tentacles
closely inflected, from immersion in a solution of phosphate of
ammonia (one part to 87,500 of water.)
FIG. 5. (Drosera rotundifolia.) Leaf (enlarged) with the tentacles on one
side inflected over a bit of meat placed on the disc.
becomes slightly incurved; the distal half in all cases remaining straight.
The short tentacles in the centre of the disc when directly excited, do
not become inflected; but they are capable of inflection if excited by a
motor impulse received from other glands at a distance. Thus, if a leaf
is immersed in an infusion of raw meat, or in a weak solution of
ammonia (if the [page 11] solution is at all strong, the leaf is paralysed),
all the exterior tentacles bend inwards (see fig. 4), excepting those near
the centre, which remain upright; but these bend towards any exciting
object placed on one side of the disc, as shown in fig. 5. The glands in
fig. 4 may be seen to form a dark ring round the centre; and this follows
from the exterior tentacles increasing in length in due proportion, as
they stand nearer to the circumference.
The kind of inflection which the tentacles undergo is best shown when
the gland of one of the long exterior
FIG. 6. (Drosera rotundifolia.) Diagram showing one of the exterior
tentacles closely inflected; the two adjoining ones in their ordinary

position.)
tentacles is in any way excited; for the surrounding ones remain
unaffected. In the accompanying outline (fig. 6) we see one tentacle, on
which a particle of meat had been placed, thus bent towards the centre
of the leaf, with two others retaining their original position. A gland
may be excited by being simply touched three or four times, or by
prolonged contact with organic or inorganic objects, and various fluids.
I have distinctly seen, through a lens, a tentacle beginning to bend in
ten seconds, after an object had been [page 12] placed on its gland; and
I have often seen strongly pronounced inflection in under one minute. It
is