Tendrils
CARELESS observation of Nature is responsible for some curious misrepresentations of her most simple facts. Even those of us who stand somewhat in the relation of nature teachers—namely, artists, both draughtsmen and painters, and from whom we have a right to expect absolute fidelity—are not free from our shortcomings as truthful chroniclers. Thus how often we see otherwise beautiful landscapes marred by features which rebel against all laws of natural philosophy—of a storm sky above a sunlit scene, for instance, spanned by the arc of the rainbow, and with all the shadows of trees and other objects thrown sidewise! Then there is that inverted or very "dry" crescent moon in western twilight skies; and how seldom do we see the beautiful law of the twining tendril appreciated in the most careful design of the botanical draughtsman!
For years the tendril was to me the conventional spiral, twisting like a continuous curl or spring from the parent branch to the support within its clasp; and it is safe to assert that not one in—well, a good many of us, who should have gone out to our grape-vine or passion-vine or melon-patch, without a previous forewarning, would have been able to tell correctly the pretty little story of its tendril methods, or have even noted the curious little kink which is the infallible peculiarity of the climbing tendril.
What is a tendril—botanically speaking? That depends. It is one thing in this plant, quite another in that, so students of vegetable anatomy or morphology soon discover.
It is soon perfectly plain that the stem is a modified root. For instance, plants have been taken up from the sod and replaced in the ground upsidedown, the roots subsequently becoming stems, and bearing leaves, and the buried leafy stems assuming the functions of roots. Leaves are mere modified branches, and the flowers modified leaves. Pistils and stamens in flowers are modified petals, or rather petals are modified stamens, the "doubling" of flowers representing the being thus accomplished, while the petals again are mere changed leaves. A neighbor of mine has a bush bearing green roses—all leaves. In the water-lily you will find it difficult to determine just where the stamen ends and the petals begin, so gradual is the blending. In the peony the same is true, and carried still further in the merging of petals and calyx into the approximate leaves.
And so it is with tendrils. In certain plants the point of the leaf, through ages of "natural selection," has gradually been prolonged into a slender arm, which clasps the branches of trees, and enables the plant thus endowed to climb higher to sun and sky, and thus to thrive more vigorously than its less fortunate brothers. The plant so advantageously equipped transmits its tendency to its offspring, and has therefore survived in place of its ancient fellows, and is the type perpetuated or "selected" by nature. Such a tendril, then, is a modified leaf. How is it in the pea? Here we find four leaflets in two opposite pairs, but no odd leaflet at the end of the main stalk, such as we see in almost all other plants of its family. But in place of this leaflet we find a branching tendril reaching out on all sides for conquest. How quietly by the aid of these eager arms the sweet-pea climbs to the top of its brush! In the common catbrier or smilax we see two slender thread-like tendrils growing from the base of each leaf. Here we have another modification, a development of the "stipule," that tiny pointed growth common to many leaves, and particularly notable at the base of a rose leaf. Still another plan has been evolved in the grape-vine. If we examine our grape arbor in June we find a number of drooping, swaying branches. The leaves are scattered singly at intervals of a few inches along the branch, each of the upper ones being attended on its opposite side by a drooping cluster of mignonette-scented blossoms. Thus they follow down towards the tip of the branch, where the clusters suddenly cease, and are replaced by long, slender, curving and branched tendrils, sometimes ten inches long. We might thus reasonably assume the tendril in this case to be a modified blossom cluster, but there is no need for us ever to assume such a thing. If we will only search with sufficient care we shall at last discover the absolute proof of the fact in a tendril which is partly in blossom, the nearest leaf-joint above it having a full cluster of blossoms, and the tendril below it, nearer the tip, not a few scattered flower-buds at its tips. This grape-vine instance may be taken as a demonstration that in no case is the tendril a special or primal organ, but merely an old one adapted to a new purpose. In one instance from a leaf, in another from a flower-stalk, just which can generally be determined by a sufficient search for the telltale intermediate form somewhere to be found on the plant.
Among the most beautiful of all tendrils are those of the passion-flower and plants of the melon family, notably the wild star-cucumber, whose portrait is here presented. It is a more or less common weed, to be found about gardens and barn-yards, where it covers the fences with its profuse, clambering growth, its stalks everywhere entangled or drawn close to support by their long, green, spiral springs, and its free, branching, young tendril tips reaching out in all directions for fresh foothold, and in its absence content at length with a friendly intertwining among themselves, and a consequent tangle of green convolutions. It is hard to believe that these long, outreaching arms at the summit of this vine are identical with the closely twisted spirals below, but such is the case; let any one of them once feel the contact of even the frailest support of twig or stalk, and it is soon close in the embrace of its eager tip, and the contraction of the spring commences, but the method of this contraction is worth our study.
In order for this tendril to coil it must twist, and it is perfectly plain on general principles that with both ends held fast twisting is impossible. But this little paradox is evidently dismissed by the tendril. If we tie a short string between two given points, and attempt to twist it with our finger and thumb, we succeed in turning the string, 'tis true, but the twist on the right side neutralizes that on the left, being in the opposite direction. In this way only can the cord be twisted. If we twist with sufficient patience we may imitate the coil of the tendril, which is performed precisely in this way. Herein lies the secret of that little loop or kink in the centre of all tendrils—a given point, which cannot be determined on the extended tendril, but whose mission is to reverse the twist in opposite directions as soon as the tip has secured its contact, and thus permit the coiling process to proceed. In tendrils of exceeding length several of these reverse loops may be found at regular intervals, sometimes as many as six in a single tendril, but the coiling process usually awaits this contact. Unsatisfied tendrils of the grape, for instance, will remain unchanged through the entire season, or until their sensitive touch has been lost. Others, like those of the passion-flower, will occasionally become discouraged and curl up all by themselves, in which case, the other tip being free, the curl is perfect and continuous and without the reverse loop, which is now unnecessary. But the function of the tendril is to clasp and hold. Its growth is not complete until thus quickened by the new responsibility. Tendrils on duty become tough and sinewy in comparison to their idling neighbors. How firm and rigid are these swollen coils upon the grape-vine!
We do not gather "figs from thistles," but some equally incongruous botanical associates are sometimes brought about through the insinuating and clambering methods of the tendril. Have we not all seen apple-trees bearing pumpkins or squashes or gourds, all originally carried thither in the form of great yellow blossoms or tender shoots! The grape-vine occasionally plays a singular botanical prank in the orchard. Here is a drooping tendril which has been swinging about for weeks from its vine canopy on the old apple-tree. It had become almost discouraged, when a chance-favoring breeze wafted its tip in contact with an apple close by. It was its last chance; with its hooked extremity it clasped the stem of the fruit, and soon made itself fast with three or four firm coils. Doubtless the little reversing loop somewhere along the tendril was also awakened from its chronic lethargy, and did its best to start the coil. Presumably it succeeded, for the pull was sufficient to dislodge the apple, which, falling to the entire length of the tendril, was still held fast in the grip, whose new responsibility had given it new strength.
And there our apple hung for weeks, swinging like a pendulum from the slender grape-vine, the coils on duty still keeping their firm grip on the stem, even though all above were straightened by the weight of the burden.