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covered with a number of minute glands,
secreting a sweet liquor which attracts the
unwary fly. Between the two lobes, just
where they join, there are three sharp bristles;
and, when a fly or any other insect crawling
over the surface of the lobes happens to touch
either of the bristles, the irritability of the
plant is excited, and the lobes, suddenly
closing, imprison the insect like a rat in a
common gin. Soon after the death of the
insect the lobes unfold, and wait for another
victim. It is supposed that this plant
requires animal food for the healthy performance
of some of its functions. In support of
this theory, it has been stated that Mr.
Knight, after having secured some plants
from the possibility of providing themselves
with flies, furnished some of them with
scraped beef, and left the rest without any
such provision. The result of the experiment
was, that the fed specimens were in a far more
flourishing condition than the unfed ones.

Another illustration of the same phenomenon
occurs among the sundews (Droseræ)
of which three species are natives of Britain.
The round leaves of these plants are covered
upon their upper surface with long hairs,
tipped with glandular and viscous globules
like dew. When an insect settles upon these
leaves, it is retained by the gumminess of the
glands; and, in a little while the hairs exhibit
their irritability by a remarkably sudden
and elastic springcurving inwards so as to
encircle the fly, and thus securely hold its
prey. These movements are attributed to
the same causes, as those of the fly-trap; but
their ultimate object is likewise unknown.

In a species of dog's-bane (Apocynum
androeamifolium) a native of the United States,
this fly-catching propensity exists, to an
equal degree, in the flowers. A little honey-bag
or nectarium, seated at the bottom of the
flower-cup, and guarded by five converging
anthers, invites the fly to enter and enjoy
the sweets; but, as soon as the little insect
inserts its proboscis between the anthers to
arrive at the honey, they close with violence
and detain him prisoner.

There are two other sensitive plants,
called the sensitive and modest acacias
(Mimosa sensitiva and pudica) which display
these movements of their leaves in a remarkable
degree. They have leaves subdivided
into four partial leaf-stalks, each furnished
with about twenty pairs of leaflets, which are
expanded horizontally during the day. When
in darkness, or touched, or irritated in any
way, each leaflet moves upward towards its
fellow on the opposite side; which, in its turn,
rises up; so that their upper surfaces come
into contact. If the movement commences
at the top of the leaf, it generally proceeds
downwards to the base; thence is
communicated to the leaflets of the next partial
leaf-stalk, and ultimately to the common leaf-stalk,
which then falls down towards the
stem. The partial leaf-stalks then converge
towards each other, having a tendency to
become parallel to the common leaf-stalk
at the extremity of which they are
suspended. When the plant is shaken by the
wind all the leaflets close simultaneously, and
the leaf-stalks droop together.

Such indeed is the sensibility of these
acacias in their native country, that the trot
of a horse will cause a whole forest of them
to droop and apparently fade. If, however,
the agitation is long continued, the plant
seems to become accustomed to the shock,
and the leaflets will expand again. This
fact has been satisfactorily ascertained by
placing some sensitive plants in a cart, and
driving them a great distance. At first the
plants became dreadfully agitated, every
leaflet hanging down against its stem; but,
soon getting used to the jolting and
gradually unfolding their leaves, they remained
fresh, and expanded for the rest of the
journey. The stem itself of the plant has
nothing whatever to do with these movements
of the leaflets, because they come from
swellings at the base of the leaf-stalks which
form a sort of knee-joint spring, or hinge,
and allow the stem to bend and lie down.

The camrunga (Averrhoa carambola) or
Coromandel gooseberry tree, possesses, like
the sensitive acacia, the faculty of moving
when touched; and is another of those
instances of irritability in the vegetable kingdom
of which we daily witness the effect,
without being able to explain the cause. The
leaves of this plant consist of alternate leaflets
with an odd one at the end; and, their common
position in the daytime, is horizontal, that is,
in the same plane with the branch on which
they grow. On being touched they move
downward, frequently with such violence
that the two opposite leaves almost touch
each other by their under sides, and the
leaflets come into contact, or even pass over
one another. By striking the branch with
the finger-nail, or any other hard substance,
the whole of the leaflets of one leaf move; or
each leaflet can be moved singly by making an
impression which shall not extend beyond it.

A wood sorrel (Oxalis seusitiva) a native
of Amboyna, is reported by Rumphius to be
so delicately sensitive, that it will not bear
the blowing of the wind upon it without
contracting its leaves; and he remarks that it
is like a maidenwho may be looked at, but
is not to be touched.

Light exercises a great influence over all
these phenomena. When a sensitive plant is
exposed to artificial light during the night its
leaves expand, and if put into a dark room
during the day the leaves close. If,
however, the plant is kept for a long time in
darkness, it will ultimately expand its leaves,
and the processes of folding and opening will
go on, although at very irregular intervals.
Any sudden degrees of heat or cold, the
vapour of boiling water, the fumes arising
from sulphur, the odour of volatile liquors, or,