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
The extremity of the tendril is almost straight and sharp. The whole
terminal portion exhibits a singular habit, which in an animal would be
called an instinct; for it continually searches for any little crevice or
hole into which to insert itself. I had two young plants; and, after
having observed this habit, I placed near them posts, which had been
bored by beetles, or had become fissured by drying. The tendrils, by
their own movement and by that of the internodes, slowly travelled over
the surface of the wood, and when the apex came to a hole or fissure it
inserted itself; in order to effect this the extremity for a length of
half or quarter of an inch, would often bend itself at right angles to
the basal part. I have watched this process between twenty and thirty
times. The same tendril would frequently withdraw from one hole and
insert its point into a second hole. I have also seen a tendril keep its
point, in one case for 20 hrs. and in another for 36 hrs., in a minute
hole, and then withdraw it. Whilst the point is thus temporarily
inserted, the opposite tendril goes on revolving.
The whole length of a tendril often fits itself closely to any surface of
wood with which it has come into contact; and I have observed one bent at
right angles, from having entered a wide and deep fissure, with its apex
abruptly re-bent and inserted into a minute lateral hole. After a
tendril has clasped a stick, it contracts spirally; if it remains
unattached it hangs straight downwards. If it has merely adapted itself
to the inequalities of a thick post, though it has clasped nothing, or if
it has inserted its apex into some little fissure, this stimulus suffices
to induce spiral contraction; but the contraction always draws the
tendril away from the post. So that in every case these movements, which
seem so nicely adapted for some purpose, were useless. On one occasion,
however, the tip became permanently jammed into a narrow fissure. I
fully expected, from the analogy of _B. capreolata_ and _B. littoralis_,
that the tips would have been developed into adhesive discs; but I could
never detect even a trace of this process. There is therefore at present
something unintelligible about the habits of this plant.
_Bignonia picta_.—This species closely resembles the last in the
structure and movements of its tendrils. I also casually examined a fine
growing plant of the allied _B. Lindleyi_, and this apparently behaved in
all respects in the same manner.
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