Vines, Tendrils, and Twining Plants

      A vine is a plant that is unable to support itself above ground. Vines must support themselves by climbing or trailing on other objects in order to orientate themselves for optimum exposure to light. Some examples of support structures include stems of other plants, fences, trellises, or just about anything the plant makes contact with.

      There are three main properties of vining plants. The first of these properties is circumnutation (searcher shoot movement). Circumnutation involves the circling of the shoot tip as it attempts to find a support host. Some shoot tips may swing as wide as one meter before a host is found and circumnutation stops. The second property is precocious internodal elongation. Early elongation of the internodes allows the vine to use its limited energy stores to find a support. The third property of vining plants is delayed leaf development. Vines expend a greater amount of energy in internodal elongation rather than leaf expansion. Large leaves would be disadvantageous while searching for a support host; the leaves would be in the way during circumnutation. Once the vine becomes securely attached to a support host, the leaves can then undergo a period of expansion.

      Vines twine, coil, or spiral around a support as a means to climb vertically. Almost any organ of a plant is capable of twining and some are highly modified for this purpose. In many plants, the stem is the twining organ. Lateral buds, lateral shoots, and petioles are the twining organs in others.

      Tendrils may be modified leaves or leaf parts, such as petioles, modified as a slender coiling structure which can support a vine by twining. Tendrils may develop at every node as lateral shoots, in an alternate pattern as modified leaves opposite photosynthetic leaves, or from serial buds in a leaf axil.

      The tendrils of Parthenocissus are modified to have disc-like tips that change their shape once they contact a substrate. The flattened discs secrete an adhesive substance that "glues" the tips to the substrate.

      Some vines have roots that grow at nodes or internodes, and these also secrete a sticky substance that "glues" the roots to the surface. These types of roots are commonly found on English ivy plants (Hedera).

Storage Shoots

      Rhizomes are shoots that grow plagiotropically (horizontally) along the surface of the ground or entirely underground. These shoot systems exhibit dorsiventral symmetry: leaves emerge from the dorsal surface and roots form the ventral surface. The leaves produce photosynthates and transfer them to the rhizome where they are stored, usually as carbohydrates, for overwintering.

      Corms are very similar to rhizomes but are usually shorter and grow orthotropically (vertically). Corms also function as storage organs of carbohydrates.

      A tuber is the swollen shoot tip of a rhizome. In the "Irish" potato (Solanum tuberosum) lateral shoots grow outward underground. The tips of these shoots swell as they store carbohydrates.

      Bulbs such as onions are short underground shoots with short internodes and many enlarged and fleshy leaf bases that store food. During the growing season the above-ground leaves ship all of their photosynthates to the bulb. Once the photosynthetic leaves die back at the end of the growing season, the apical meristem dies also. The following spring, one of the lateral buds near to where the apical meristem was initiates regrowth.

      In many so-called root crops like turnips and beets, the hypocotyl (shoot region below the cotyledons) may swell and become part of the storage organ along with the primary root.