The Movements and Habits of Climbing PlantsDarwin, Charles
Science
The Movements and Habits of Climbing Plants
Darwin, Charles
Climbing plants; Geotropism; Plants; Plants -- Irritability and movements
LILIACEÆ.—_Gloriosa Plantii_.—The stem of a half-grown plant continually
moved, generally describing an irregular spire, but sometimes oval
figures with the longer axes directed in different lines. It either
followed the sun, or moved in an opposite course, and sometimes stood
still before reversing its direction. One oval was completed in 3 hrs.
40 m.; of two horseshoe-shaped figures, one was completed in 4 hrs. 35 m.
and the other in 3 hrs. The shoots, in their movements, reached points
between four and five inches asunder. The young leaves, when first
developed, stand up nearly vertically; but by the growth of the axis, and
by the spontaneous bending down of the terminal half of the leaf, they
soon become much inclined, and ultimately horizontal. The end of the
leaf forms a narrow, ribbon-like, thickened projection, which at first is
nearly straight, but by the time the leaf gets into an inclined position,
the end bends downwards into a well-formed hook. This hook is now strong
and rigid enough to catch any object, and, when caught, to anchor the
plant and stop the revolving movement. Its inner surface is sensitive,
but not in nearly so high a degree as that of the many before-described
petioles; for a loop of string, weighing 1.64 grain, produced no effect.
When the hook has caught a thin twig or even a rigid fibre, the point may
be perceived in from 1 hr. to 3 hrs. to have curled a little inwards;
and, under favourable circumstances, it curls round and permanently
seizes an object in from 8 hrs. to 10 hrs. The hook when first formed,
before the leaf has bent downwards, is but little sensitive. If it
catches hold of nothing, it remains open and sensitive for a long time;
ultimately the extremity spontaneously and slowly curls inwards, and
makes a button-like, flat, spiral coil at the end of the leaf. One leaf
was watched, and the hook remained open for thirty-three days; but during
the last week the tip had curled so much inwards that only a very thin
twig could have been inserted within it. As soon as the tip has curled
so much inwards that the hook is converted into a ring, its sensibility
is lost; but as long as it remains open some sensibility is retained.
Whilst the plant was only about six inches in height, the leaves, four or
five in number, were broader than those subsequently produced; their soft
and but little-attenuated tips were not sensitive, and did not form
hooks; nor did the stem then revolve. At this early period of growth,
the plant can support itself; its climbing powers are not required, and
consequently are not developed. So again, the leaves on the summit of a
full-grown flowering plant, which would not require to climb any higher,
were not sensitive and could not clasp a stick. We thus see how perfect
is the economy of nature.
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