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the formation of a new organism from part of the parental body. The methods of vegetative reproduction found in nature are varied. The simplest is the creation of an organism from a single vegetative cell as a result of its successive division and the differentiation of the cells formed.
Vegetative reproduction is characteristic of microorganisms, simple animals, and almost all plants. In animals, vegetative reproduction is achieved by budding (for example, in sponges, coelenterates, and bryozoans) or fission (for example, in protozoans); in unicellular plants (algae, fungi, and others), generally by fission, less commonly by budding; in lower multicellular plants, by disintegration of the body into separate parts capable of regeneration. Higher plants reproduce by forming rhizomes, suckers, bulbs, tubers, and other vegetative organs. In many cultivated plants vegetative reproduction is the only means of retaining valuable strain characteristics and properties.
Higher plants may reproduce by layering (for example, fir, rhododendron, and wild grape forms)—that is, by parts of organs whose contact with the parental plant is maintained until they begin to take up nutrients independently, by forming vines or runners (strawberry, blackberry, sweet potato, creeping buttercup, ground ivy, and others), and by forming root suckers (many deciduous and coniferous trees and grasses, such as mountain ash, rose, alder, tausaghyz, and field sow thistle). Many vegetables and ornamental plants reproduce by forming bulbs or tubers (such as onion, tulip,” lily, potato, and sweet potato) and rhizomes (generally such perennials as lily of the valley, mint, asparagus, bamboo, and many weeds). Many plants are propagated by cuttings (stem, root, or leaf cuttings). Natural reproduction by leaves is characteristic of kalanchoe in which the shoots formed on the leaf blades fall down and become rooted in the soil.
Fruit growers use scion-rooted methods of vegetative reproduction (propagation by layering and use of cuttings) and grafting. A layer is part of the above-ground stem with buds that is not separated from the parental plant during the rooting period. The stems that are to be rooted are hilled up. Rooted stems are separated from the parental plant, cut into pieces (with roots), and immediately set out in the field or allowed to grow in the nursery (for one to two years). Many species of agricultural and ornamental plants (blackberry, ivy, sumac, smoke tree, rhododendron, and others) reproduce by natural layering. Fruit growers generally propagate plants by vertical and horizontal layering, for example, many gooseberry varieties and some types of apple stock, while horticulturists use this method for lilac, viburnum, honeysuckle, and other plants. Many blackberry and blackcap raspberry varieties are propagated by apical layering.
In propagation by cuttings, use is made of parts of the plant (cuttings) capable under certain conditions of producing roots (on stems) or buds (on roots) or buds and roots (on leaves). Stem, leaf, and root cuttings are distinguished. Stem cuttings may be without leaves (winter cuttings) or with leaves (summer, or green cuttings), herbaceous or woody. Leafless cuttings are usually obtained in the fall, generally from one-year-old shoots that are cut into pieces 20-30 cm long and set out in the fall or spring after being kept heeled in a cellar or in snow. Grapes, some gooseberry varieties, some types of apple and plum stock, quince, fig, pomegranate, spirea, jasmine, poplar, willow, and others are propagated by winter cuttings. Leafy shoots cut into pieces 5-10 cm long are used for green cuttings. Sometimes part of the bark with lignin and one bud is cut from the stem (leaf-bud cuttings). Green cuttings are used to propagate gooseberry, cherry, plum, quince, sea buckthorn, olive, and many ornamental shrubs and herbaceous flowering plants such as chrysanthemum, geranium, pinks, dahlia, and phlox.
In green cuttings from many plants the rooting process is stimulated by means of growth substances. Green cuttings from cherry, plum, lilac, and other plants are easily rooted when the shoots being propagated are growing rapidly in length; in the apple, gooseberry, and other plants, at the end of this phase; in the black currant and some gooseberry varieties, throughout the entire growth phase. The propagation of plants by green cuttings is heavily dependent on the temperature (20° to 25° C is optimal), air humidity, moisture content of the substrate, and light conditions. When green cuttings are used, an artificial mist is created by automatic systems over the place where the cuttings are rooting. The rooting ability of cuttings increases sharply in such an atmosphere, and the amount of labor involved is reduced by twofold or threefold.
A leaf cutting is a leaf or part of a leaf. The leaf is set in a rooting medium (generally sand with the petiole or with the under side down after prominent veins are lightly incised. A little sand is added, and then the rooting medium is watered. Leaf cuttings are used to propagate begonia, sedum, African violet, and other plants.
Root cuttings are part of a root. They are generally prepared in the fall, are 10-15 cm long, kept heeled in sand and peat, and set out in fertile soil in the spring. Root cuttings are used to propagate red raspberries, blackberries, young apple seedlings, some cherry and plum varieties, and other plants.
REFERENCESKrenke, N. P. Regeneratsiia rastenii . Moscow-Leningrad, 1950.
Turetskaia, R. Kh. Fiziologiia korneobrazovaniia u cherenkov i stimuliatory rosta. Moscow, 1961.
Hartmann, H. T., and D. E. Kester. Razmnozhenie sadovykh rastenii. Moscow, 1963. (Translated from English.)
Zhukovskii, P. M. Botanika, 4th ed. Moscow, 1964.
M. T. TARASENKO