The tendrils of Bryonia dioica, Cucurbita ovifera, and Cucumis sativa are sensitive and revolve. Whether the internodes likewise revolve I did not observe. In Anguria Warscewiczii, the internodes, though thick and stiff, revolve: in this plant the lower surface of the tendril, some time after clasping a stick, produces a coarsely cellular layer or cushion, which adapts itself closely to the wood, like that formed by the tendril of the Hanburya; but it is not in the least adhesive. In Zanonia Indica, which belongs to a different tribe of the family, the forked tendrils and the internodes revolve in periods between 2 hrs. 8 m. and 3 hrs. 35 m., moving against the sun.

VITACEAE.--In this family and in the two following, namely, the Sapindaceae and Passifloraceae, the tendrils are modified flower- peduncles; and are therefore axial in their nature. In this respect they differ from all those previously described, with the exception, perhaps, of the Cucurbitaceae. The homological nature, however, of a tendril seems to make no difference in its action.

Vitis vinifera.--The tendril is thick and of great length; one from a vine growing out of doors and not vigorously, was 16 inches long. It consists of a peduncle (A), bearing two branches which diverge equally from it. One of the branches (B) has a scale at its base; it is always, as far as I have seen, longer than the other and often bifurcates. The branches when rubbed become curved, and subsequently straighten themselves. After a tendril has clasped any object with its extremity, it contracts spirally; but this does not occur (Palm, p. 56) when no object has been seized. The tendrils move spontaneously from side to side; and on a very hot day, one made two elliptical revolutions, at an average rate of 2 hrs. 15 m. During these movements a coloured line, painted along the convex surface, appeared after a time on one side, then on the concave side, then on the opposite side, and lastly again on the convex side. The two branches of the same tendril have independent movements. After a tendril has spontaneously revolved for a time, it bends from the light towards the dark: I do not state this on my own authority, but on that of Mohl and Dutrochet. Mohl (p. 77) says that in a vine planted against a wall the tendrils point towards it, and in a vineyard generally more or less to the north.

The young internodes revolve spontaneously; but the movement is unusually slight. A shoot faced a window, and I traced its course on the glass during two perfectly calm and hot days. On one of these days it described, in the course of ten hours, a spire, representing two and a half ellipses. I also placed a bell-glass over a young Muscat grape in the hot-house, and it made each day three or four very small oval revolutions; the shoot moving less than half an inch from side to side. Had it not made at least three revolutions whilst the sky was uniformly overcast, I should have attributed this slight degree of movement to the varying action of the light. The extremity of the stem is more or less bent downwards, but it never reverses its curvature, as so generally occurs with twining plants.

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 Movements and Habits of Climbing Plants Page 47

Charles Darwin

Free Books in the public domain from the Classic Literature Library ©

Charles Darwin

All Pages of This Book