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 tendrils are similar in structure to those of the last species. They
continue growing for some time, even after they have clasped an object.
When fully grown, though borne by a young plant, they are 9 inches in
length. The three divergent toes are shorter relatively to the tarsus
than in the former species; they are blunt at their tips and but slightly
hooked; they are not quite equal in length, the middle one being rather
longer than the others. Their outer surfaces are highly sensitive; for
when lightly rubbed with a twig, they became perceptibly curved in 4 m.
and greatly curved in 7 m. In 7 hrs. they became straight again and were
ready to re-act. The tarsus, for the space of one inch close to the
toes, is sensitive, but in a rather less degree than the toes; for the
latter after a slight rubbing, became curved in about half the time.
Even the middle part of the tarsus is sensitive to prolonged contact, as
soon as the tendril has arrived at maturity. After it has grown old, the
sensitiveness is confined to the toes, and these are only able to curl
very slowly round a stick. A tendril is perfectly ready to act, as soon
as the three toes have diverged, and at this period their outer surfaces
first become irritable. The irritability spreads but little from one
part when excited to another: thus, when a stick was caught by the part
immediately beneath the three toes, these seldom clasped it, but remained
sticking straight out.
The tendrils revolve spontaneously. The movement begins before the
tendril is converted into a three-pronged grapnel by the divergence of
the toes, and before any part has become sensitive; so that the revolving
movement is useless at this early period. The movement is, also, now
slow, two ellipses being completed conjointly in 24 hrs. 18 m. A mature
tendril made an ellipse in 6 hrs.; so that it moved much more slowly than
the internodes. The ellipses which were swept, both in a vertical and
horizontal plane, were of large size. The petioles are not in the least
sensitive, but revolve like the tendrils. We thus see that the young
internodes, the petioles, and the tendrils all continue revolving
together, but at different rates. The movements of the tendrils which
rise opposite one another are quite independent. Hence, when the whole
shoot is allowed freely to revolve, nothing can be more intricate than
the course followed by the extremity of each tendril. A wide space is
thus irregularly searched for some object to be grasped.
One other curious point remains to be mentioned. In the course of a few
days after the toes have closely clasped a stick, their blunt extremities
become developed, though not invariably, into irregular disc-like balls
which have the power of adhering firmly to the wood. As similar cellular
outgrowths will be fully described under _B. capreolata_, I will here say
nothing more about them.
Public-domain text, read in full here on John Shaqi.
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