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
With respect to the abortion of tendrils, certain cultivated varieties of
_Cucurbita pepo_ have, according to Naudin, {200} either quite lost these
organs or bear semi-monstrous representatives of them. In my limited
experience, I have met with only one apparent instance of their natural
suppression, namely, in the common bean. All the other species of
_Vicia_, I believe, bear tendrils; but the bean is stiff enough to
support its own stem, and in this species, at the end of the petiole,
where, according to analogy, a tendril ought to have existed, a small
pointed filament projects, about a third of an inch in length, and which
is probably the rudiment of a tendril. This may be the more safely
inferred, as in young and unhealthy specimens of other tendril-bearing
plants similar rudiments may occasionally be observed. In the bean these
filaments are variable in shape, as is so frequently the case with
rudimentary organs; they are either cylindrical, or foliaceous, or are
deeply furrowed on the upper surface. They have not retained any vestige
of the power of revolving. It is a curious fact, that many of these
filaments, when foliaceous, have on their lower surfaces, dark-coloured
glands like those on the stipules, which excrete a sweet fluid; so that
these rudiments have been feebly utilized.
One other analogous case, though hypothetical, is worth giving. Nearly
all the species of _Lathyrus_ possesses tendrils; but _L. nissolia_ is
destitute of them. This plant has leaves, which must have struck
everyone with surprise who has noticed them, for they are quite unlike
those of all common papilionaceous plants, and resemble those of a grass.
In another species, _L. aphaca_, the tendril, which is not highly
developed (for it is unbranched, and has no spontaneous revolving-power),
replaces the leaves, the latter being replaced in function by large
stipules. Now if we suppose the tendrils of _L. aphaca_ to become
flattened and foliaceous, like the little rudimentary tendrils of the
bean, and the large stipules to become at the same time reduced in size,
from not being any longer wanted, we should have the exact counterpart of
_L. nissolia_, and its curious leaves are at once rendered intelligible
to us.
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