CLIMBING PLANTS
Vitaceae is a family of lianas—woody vines—with broad lobed leaves and tendrils and inflorescences that are opposite to the leaves, easy to recognize even in the absence of flowers or fruits. The word “vine” originally referred only to Vitis but now is considered a term for herbaceous climbing plants; “liana” refers to woody climbers. The genus Vitis includes around sixty species of grapes, twenty-five of which are found in North America.
The Old World species Vitis vinifera is well worth raising a glass to. Thought to have come into cultivation in the trans-Caucasus region by at least 6000 BCE, the locus of the oldest known viticultural tradition, it arrived in western Europe by around 1500 BCE and is now cultivated worldwide in regions with hot dry summers and cold wet winters. Vitis species and its hybrids are cultivated for the production of fresh table grapes, dried raisins, grape juice, and vinegar—even the leaves have their uses, such as stuffed dolma—but most significantly, wine production constitutes an estimated 80 percent of cultivation. Nowadays an estimated 10,000 cultivars are recognized, with many grafted onto the rootstocks of native North American grape species to protect them from the devastating grape phylloxera (Daktulosphaira vitifoliae), an aphid relative native to North America that almost wiped out the European vines.
Darwin was known to enjoy wine and port on occasion. In one record of undergraduate hijinks, he lost a bet on the height of the ceiling in the old Combination Room at Christ’s College, Cambridge, costing him—or rather his father, who was footing his university bills—a bottle of port.1 Later in life he got more serious, including on the subject of Vitis. He grew grapevines in his garden and studied the development of their tendrils closely. Documenting a graduated series from peduncle to tendril, Darwin came to believe that tendrils represent modified inflorescence stems, or peduncles—a departure from the tendrils of most species, which are mostly derived from leaves or stems. He also observed the related genera Cissus and Ampelopsis (now Parthenocissus), along with species in two other families, Sapindaceae and Passifloraceae, all of which, he concluded, also have tendrils derived from flower-peduncles.
This is accepted today, but Darwin had a difficult time convincing his botanist friends. Each had a different opinion on the origin of tendrils, at least certain kinds. Take gourds and others in the Cucurbitaceae family. Asa Gray was convinced their tendrils are modified branches; Darwin’s old mentor John Stevens Henslow at Cambridge maintained that they are modified stipules; and botanist Thomas Thomson was sure they represent modified leaves. Darwin spent many months studying tendril development in different groups, comparing them closely to trace out homologies. At one point he was thinking all were derived from leaves, writing to Hooker half-jokingly, “Every thing [would] go very beautifully for me if botanists [would] let all tendrils be modified leaves.”156 Vitis and Passiflora vines soon changed his mind. He ran his analysis by Daniel Oliver, at Kew, writing, “Does not this render it highly probable that the tendril is a modified flower with its peduncle?” Like the others, Oliver did not fully agree, and the conversation continued.157 Darwin stuck to his position, concluding in Climbing Plants that while all tendrils performed the same function, they were, depending on the plant, derived from different organs, including leaves, flower-peduncles, and possibly branches and stipules.158 Botanists studying tendril evolution today largely agree, recognizing some seventeen different kinds of tendril.159
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 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 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 believe that the tendrils of the vine are modified flower-peduncles. I here give a drawing (right) 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, left) 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.
Tendril of the vine (left). Flower-stalk of the vine (right).
The lower and naked part of the sub-peduncle (C) is likewise slightly sensitive to a rub, and I have seen it bent round a stick and even partly round a leaf with which it had come into contact. That the sub-peduncle has the same nature as the corresponding branch of an ordinary tendril, is well shown when it bears only a few flowers; for in this case, it becomes less branched, increases in length, and gains both in sensitiveness and in the power of spontaneous movement. I have twice seen sub-peduncles which bore from thirty to forty flower-buds, and which had become considerably elongated and were completely wound round sticks, exactly like true tendrils. …
The gradations from the ordinary state of a flower-stalk, as represented in the drawing (right), to that of a true tendril (left) are complete. We have seen that the sub-peduncle (C), whilst still bearing from thirty to forty flower-buds, sometimes becomes a little elongated and partially assumes all the characters of the corresponding branch of a true tendril. From this state, we can trace every stage till we come to a full-sized perfect tendril, bearing on the branch which corresponds with the sub-peduncle one single flower-bud! Hence there can be no doubt that the tendril is a modified flower-peduncle.
Oxalis versicolor. Watercolor on vellum by Pancrace Bessa for Herbier Général de l’Amateur.