Horticulturist pp. 266-269 (1849)
John Claudius Loudon
3. Propagation by Leaves.
This mode of propagation is of considerable antiquity, though it has not till lately been much practised. It is said by Agricola, (L'Agriculteur Parfait, &c., ed. 1732) to be the invention of Frederick, a celebrated gardener at Augsburg, and to have been first described by Mirandola, in his Manuale di Giardinieri, published in 1652. Subsequent experiments by C. Bonnet, of Geneva; Noisette, Thouin, Neuman, and Pepin, of Paris; Knight, Herbert, and others, in England; and quite recently by Lucas, in Germany, have proved that there is no class of plants which might not be propagated by leaves. It has been tried with success with cryptogamous plants, with endogens and exogens; with the popular divisions of ligneous and herbaceous plants, annuals, biennials, and perennials, and with the leaves of bulbous plants and palms.
609. The principle on which the propagation of plants by leaves is founded is considered by some as the organisability of the sap of the plant, and by others as founded on the universal diffusion through the plant of embryo buds. "That the vital power residing in the latex or blood of the plant," Mr. Lymburn observes, "is sufficient to form buds, no one can doubt who has observed the matter extravasated at times from the stems of geraniums, dahlias, &c, and the stumps of old trees. At first it is only a mass of cellular matter, but gradually begins to thicken on the surface, and get of a red and green colour; vessels are seen to be produced and buds organised, which, if placed in favourable circumstances, will evolve into shoots. I have seen the buds literally crowded together like bees in a hive. Dr. Carpenter says, that the blood of animals, even when altogether separated and spread out, has been seen to organise vessels, from the strength of the vital principle." This seems also to have been Mr. Knight's opinion. It is, however, of less consequence to adopt either theory than to follow a practice which has been found successful by cultivators, and which takes place in nature in the leaves accidentally broken and left on moist soil of cardamine hirsuta, the common water-grass, sedums, and other succulent-leaved plants, and probably various others, independently of those which root by the leaves in consequence of these producing bulbs, as in the case of Woodwardia radicans (608).
610. The conditions generally required for rooting leaves are, that the leaf be nearly full grown; that it be taken off with the petiole entire; that the petiole be inserted from an eighth to half an inch, according to its length, thickness, and texture, in sandy loam, or in pure sand on a stratum of rich soil; and that both the soil and the atmosphere be kept uniformly moist, and at a higher temperature than is required for rooted plants of the same species. The leaves of such succulents as cacalia, crassula, cotyledon, kalankoe, portulaca, sedum, sempervivum, cactus, and similar plants, root when laid on the surface of soil, with the upper side to the light, and the soil and atmosphere is kept sufficiently close, moist, and warm. The first change that takes place is the formation of a callosity at the base of the petiole; after which, at the end of a period, which varies greatly in different plants, roots are produced, and eventually, at an equally varying period, a bud from which a leafy axis is developed. M. Pepin states that rooted leaves of Hoya carnosa, and those of several kinds of Aloe, did not produce a bud till after the lapse of ten or twelve years. The leaves before they emit roots must be slightly shaded to prevent excessive perspiration during sunshine, but afterwards they may be fully exposed to the light.
|Fig. 178. The lower half of the leaf of theophrasta rooted and sending up a shoot.||Fig. 179. The upper half of theophrasta rooted and sending up a shoot.|
611. Rooting portions of leaves. It appears that some leaves will throw down roots with only a part of the petiole attached, and that others will even root from the mid-rib when the leaf is cut through. In 1839, M. Neuman, of the Paris Garden, seeing the theophrasta latifolia (Clavija ornata, D. Don) growing so well from cuttings of leaves, conceived the idea of cutting several.of them in two, and treating them in the same manner as entire leaves. Accordingly, he cut a leaf in two, and planted both parts in the same pot, treating them exactly alike. In about tliree months, the lower half of the leaf (fig. 178) had made roots, but the upper half had none; though, some time afterwards, when it became necessary to separate the cuttings, M. Neuman found that the upper part of the leaf had also made roots (fig. 179), but that these roots were much shorter than those of the lower half. The rooting of the two halves of a leaf of the theophrasta, so hard and dry as every one knows these leaves to be, appearing to him an interesting circumstance, he continued to pay attention to them for six months. He wished to ascertain if they would produce buds as in other cases, for he was in hopes they would, as he remarked that the roots increased in the pot. At last in the seventh month, for the first time, he saw at the extremity of his two half leaves, buds appearing, as well formed as those proceeding from the base of the petiole of an entire leaf. In June, 1840, these two cuttings had become beautiful and healthy plants, which it was impossible to distinguish from others produced from entire leaves.
We see from this experiment that it requires double the time to produce a bud from the upper part of a leaf, that it requires for the lower half to produce one; and that, in propagations by leaves, it is not always necessary to take the heel or lower end of the petiole with the leaf, which sometimes injures and deforms the shoots. M. Neuman's experiment proves further, that wherever cambium can be formed, there are at the same time a number of utricnles or germs of buds formed, from which a new plant will be developed when the parent is placed in favourable circumstances. From this circumstance, in short, we may conclude that all the veins may serve for the reproduction of plants. The dots in fig 179 show the parts of the upper half-leaf which were cut off to allow of its being put into a small pot; and this proves that it is only the middle rib (or prolongation of the petiole), which is required for reproduction. Half leaves of various plants have been rooted in charcoal in Germany (603).
612. The plants usually raised by leaves in British gardens are comparatively few, and chiefly gesneras, gloxinias; bulb-bearing leaves, such as bryophyllum; some succulents, such as sempervivum, and a few others. Leaves of the orange, the hoya, the aucuba, the camellia, ficus elasticus, the clianthus, the common laurel, and a few more, are occasionally rooted, but more as matter of curiosity than for the purpose of increase.
613. Propagation by the leaves of bulbs has been successfully effected by the Hon. and Rev. W. Herbert, who first tried it, in 1809, by setting a cutting of a leaf of a Cape Ornithogalum. "The leaf was cut off just below the surface of the earth in an early stage of its growth, before the flower-stalk had begun to rise; and it was set in the earth, near the edge of the pot in which the mother plant was growing, and so left to its fate. The leaf continued quite fresh, and on examination (while the bulb was flowering) a number of young bulbs and radical fibres were found adhering to it. They appeared to have been formed by the return of the sap which had nourished the leaf. Thereupon two or three more leaves were taken off and placed in like situations; but they turned yellow, and died without producing any bulbs. It appeared to me then, and it was confirmed by subsequent experience, that in order to obtain a satisfactory result the leaf must be taken off while the plant is advancing in its growth. I found it easy thus to multiply some bulbs that did not willingly produce offsets. I afterwards tried, without cutting the leaf off, to make an oblique incision in it under ground, and in some cases just above ground, attempting, in fact, to raise bulbs by layering the leaf. This attempt was also successful, and some young bulbs were formed on the edge of the cut above ground as well as below. I tried cuttings of the stem of some species of Lilium, and obtained bulbs at the axil of the leaf, as well as from the scales of the bulb; and that practice has been since much resorted to by gardeners, though I believe it originated with me. I raised a great number of bulbs of the little plant which has been successively called massonia, scilla, and hyacinthus corymbosus, by setting a pot full of its leaves, and placing a bell-glass over them for a short time. A bulb was obtained with equal facility from a leaf of a rare species of Encomia; and experiments with the leaves of Lachenalias were equally successful. I apprehend that all liliaceous bulbs may be thus propagated; but the more fleshy the leaf, the more easily the object will be attained." (Gard. Chron., for 1841, p. 381.)
614. Rooting leaves and parts of leaves in powdered charcoal. Leaves and parts of leaves of the following plants were rooted in charcoal, by M. Lucas, of Munich, in 1839. Half-leaves of Piereskia, Polianthes mexicana Zuccar., and leaves of Euphorbia fastuosa, in a short time filled their pots so full of roots that they were obliged to be repotted.
In from eight to fourteen days leaves of Cecropia palmata, Oxalis mandioccana, O. purpurea, Euphorbia fastuosa, Cyclamen indicum, Lophospermum scandens, Martyna craniolaria, Begonia monoptera, B. bulbifera, Ipomoea superba, I. spec, e Corcovado, Mesembryanthemum tigrinum, Gesnera latifolia, G. atrasanguinea, Sinningia guttata, Piper piereskiaefolium, all sorts of Gloxinia, even calices and mere flower-stems, pieces of leaves of Convolvulus Batatas, Peireskia grandifolia, Polianthes mexicana, and warts of the large-warted mammillaria.
In three weeks the tops of the leaves of Agave americana fol. var., leaves of Jacaranda brasiliensis, bundles of leaves of Pinus cxcelsa, leaves of Mimosa Houstoni, and Cyperus vaginatus.
In five weeks, whole and half-cut folioles of Encephalartos caffer and Zamia integrifolia produced a number of roots from the surface of the cuts.
Many leaves have not yet made roots, but for a considerable time have formed callosities; such as Laurus nitida, Bignonia Telfairae, Carolinea princeps, Ardisiae, Gardenia, Adansonia digitata, Dracaena, &c. As experiments that did not succeed, we may mention portions of the leaves of Amaryllis and Crinum, of ferns, of tropical Orchideae, of Dasylirion and Hechtia, Tillandsia, Pandanus, Phormium tenax, of tropical tuberous-rooted Aroideae, old leaves of the Agave, and some others which, partly through rotting by wet, or other mischances, were prevented from growing.
615. Leaves with the buds in the axils root freely in the case of many species. The buds and leaves are cut out with a small portion of the hark and alburnum to each, and planted in sandy loam, so deep as just to cover the bud; the soil being pressed firmly against it, and the back of the leaf resting on the surface of the soil. Covered with a bell-glass and placed on heat, in a short time the buds break through the surface of the soil, and elongate into shoots. The late Mr. Knight tried this mode with double camellias, magnolias, metrosideros, acacias, neriums, rhododendrons, and many others, some of which rooted and made shoots the same season, and others not till the following spring.