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
_Bignonia capreolata_.—We now come to a species having tendrils of a
different type; but first for the internodes. A young shoot made three
large revolutions, following the sun, at an average rate of 2 hrs. 23 m.
The stem is thin and flexible, and I have seen one make four regular
spiral turns round a thin upright stick, ascending of course from right
to left, and therefore in a reversed direction compared with the before
described species. Afterwards, from the interference of the tendrils, it
ascended either straight up the stick or in an irregular spire. The
tendrils are in some respects highly remarkable. In a young plant they
were about 2½ inches in length and much branched, the five chief branches
apparently representing two pairs of leaflets and a terminal one. Each
branch is, however, bifid or more commonly trifid towards the extremity,
with the points blunt yet distinctly hooked. A tendril bends to any side
which is lightly rubbed, and subsequently becomes straight again; but a
loop of thread weighing ¼th of a grain produced no effect. On two
occasions the terminal branches became slightly curved in 10 m. after
they had touched a stick; and in 30 m. the tips were curled quite round
it. The basal part is less sensitive. The tendrils revolved in an
apparently capricious manner, sometimes very slightly or not at all; at
other times they described large regular ellipses. I could detect no
spontaneous movement in the petioles of the leaves.
Whilst the tendrils are revolving more or less regularly, another
remarkable movement takes place, namely, a slow inclination from the
light towards the darkest side of the house. I repeatedly changed the
position of my plants, and some little time after the revolving movement
had ceased, the successively formed tendrils always ended by pointing to
the darkest side. When I placed a thick post near a tendril, between it
and the light, the tendril pointed in that direction. In two instances a
pair of leaves stood so that one of the two tendrils was directed towards
the light and the other to the darkest side of the house; the latter did
not move, but the opposite one bent itself first upwards and then right
over its fellow, so that the two became parallel, one above the other,
both pointing to the dark: I then turned the plant half round; and the
tendril which had turned over recovered its original position, and the
opposite one which had not before moved, now turned over to the dark
side. Lastly, on another plant, three pairs of tendrils were produced at
the same time by three shoots, and all happened to be differently
directed: I placed the pot in a box open only on one side, and obliquely
facing the light; in two days all six tendrils pointed with unerring
truth to the darkest corner of the box, though to do this each had to
bend in a different manner. Six wind-vanes could not have more truly
shown the direction of the wind, than did these branched tendrils the
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