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
Various authors (Palm, p. 55; Mohl, p. 45; Lindley, &c.) believe that the
tendrils of the vine are modified flower-peduncles. I here give a
drawing (fig. 10) of the ordinary state of a young flower-stalk: it
consists of the “common peduncle” (A); of the “flower-tendril” (B), which
is represented as having caught a twig; and of the “sub-peduncle” (C)
bearing the flower-buds. The whole moves spontaneously, like a true
tendril, but in a less degree; the movement, however, is greater when the
sub-peduncle (C) does not bear many flower-buds. The common peduncle (A)
has not the power of clasping a support, nor has the corresponding part
of a true tendril. The flower-tendril (B) is always longer than the
sub-peduncle (C) and has a scale at its base; it sometimes bifurcates,
and therefore corresponds in every detail with the longer scale-bearing
branch (B, fig. 9) of the true tendril. It is, however, inclined
backwards from the sub-peduncle (C), or stands at right angles with it,
and is thus adapted to aid in carrying the future bunch of grapes. When
rubbed, it curves and subsequently straightens itself; and it can, as is
shown in the drawing, securely clasp a support. I have seen an object as
soft as a young vine-leaf caught by one.
The lower and naked part of the sub-peduncle (C) is likewise slightly
sensitive to a rub, and I have seen it bent round a stick and even partly
round a leaf with which it had come into contact. That the sub-peduncle
has the same nature as the corresponding branch of an ordinary tendril,
is well shown when it bears only a few flowers; for in this case it
becomes less branched, increases in length, and gains both in
sensitiveness and in the power of spontaneous movement. I have twice
seen sub-peduncles which bore from thirty to forty flower-buds, and which
had become considerably elongated and were completely wound round sticks,
exactly like true tendrils. The whole length of another sub-peduncle,
bearing only eleven flower-buds, quickly became curved when slightly
rubbed; but even this scanty number of flowers rendered the stalk less
sensitive than the other branch, that is, the flower-tendril; for the
latter after a lighter rub became curved more quickly and in a greater
degree. I have seen a sub-peduncle thickly covered with flower-buds,
with one of its higher lateral branchlets bearing from some cause only
two buds; and this one branchlet had become much elongated and had
spontaneously caught hold of an adjoining twig; in fact, it formed a
little sub-tendril. The increasing length of the sub-peduncle (C) with
the decreasing number of the flower-buds is a good instance of the law of
compensation. In accordance with this same principle, the true tendril
as a whole is always longer than the flower-stalk; for instance, on the
same plant, the longest flower-stalk (measured from the base of the
common peduncle to the tip of the flower-tendril) was 8½ inches in
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