PROPAGATION BY LEAVES
UNDER certain conditions buds are formed on the leaves, the roots, or the flower-stems of a large number of plants; such buds being called adventitious, to distinguish them from the stem or normal buds, that are found present on all plants, and which are borne in the axils of the leaves. It is supposed that the leaves of a very large proportion of plants possess this power to develop extraordinary buds, and that their failing to do so when tested by the gardener is due to improper treatment rather than to absolute impotence in the leaf itself. It is, however, only in a few eases that leaf-cuttings are resorted to for purposes of propagation, such plants as Begonia, Gloxinia, Echeveria, and a few others, of more or less succulent nature, being the only ones for the increase of which leaf-cuttings are employed. Numerous other plants have proved Capable of propagation by this means, some of them being not at all succulent-leaved, while, on the other hand, plants of excessive succulence have proved unable to form buds when tested in the same way. In some cases where leaf-cuttings have been tried, roots were freely developed, but no bud was formed. Ficus elastica, Camellias, and Hoya carnosa may be mentioned as plants whose leaves root freely but do not develop buds, although left in the propagating house for several years. Lindley states that the leaves of Roses strike freely, but will not form buds, a peculiarity which, along with the above, is supposed to belong to the nature of species, and is not easily explained.
Where it is desirable that a new plant should be propagated as abundantly and rapidly as possible, it will be found often advantageous to place the leaves that are removed from stem-cuttings in the propagating-frame, and treat as advised below. That success might come when least expected may be seen by the following list, which comprises plants capable of propagation by leaf-cuttings. To any one acquainted with the nature of these plants, it will be apparent that no rule can be laid down for the guidance of the cultivator, either when based on the texture of the leaves or the nature of the plants.
List of plants that may be propagated by means of leaves or portions of leaves:—
In this list only those plants are included whose leaves have proved able to form buds capable of developing into plants, and it will be understood that a large number of plants might be added to the above if their leaves were tested. This method of propagation is only rarely resorted to; a fact which accounts for the smallness of the number of plants known to be amenable to it.
Turning now to the plants that are usually increased from cuttings made of leaves, a word may be said on the treatment such leaves require, and the best time of year for the operation. Gloxinias may be dealt with at all times of the year when leaves are obtainable, the most favourable period being autumn. Well-matured leaves should be selected, avoiding those in which the yellowness of decay has appeared. The leaf-stalk may be severed at any point, it being unnecessary to secure thorn with a heel or portion of the stem. The blade may then be divided longitudinally, so that a large leaf would form about half a dozen cuttings. It is, however, better when the blade is cut into sections, each section having a portion of the midrib attached to its base. Some prefer severing the midrib into about a dozen pieces, leaving the blade intact. In this way a plant is obtained from each portion of the midrib, bulbils being developed on the lower end of each. Where the latter plan is adopted the whole leaf must be pegged on to a pan of sandy soil. If the leaf is divided up into smaller pieces, cutting-pots may be used, filling the pots half full of drainage, and the other half with a light sandy soil. Into this the cuttings must be placed, obliquely, so that whilst held firmly in the soil their bases are only a little below the surface. A hot-bed or close flume in a propagating-house will be the most suitable place for the cuttings till rooted. In a small moist stove, a position on a shelf near the glass would answer equally well for Gloxinia cuttings.
Bertolonias may be increased from healthy ripened leaves, which, if the midrib be nicked in several places, and the whole leaf then pegged on to a pot of very sandy peat, soon form roots and tiny tubers at every incision, if placed in a moist propagating frame. For these plants autumn is the most suitable season, the leaves at that time being more vigorous than at any other. B. Van Houtteana is easily increased from leaf-cuttings; B. Marmorata and one or two others sometimes produce good seed, from which abundance of plants may be obtained.
Gasterias, Haworthias, Echeverias, Sempervivums, and such-like succulents, are easily propagated from leaves. The nature of these plants is such as to enable any portion of them to remain fresh and plump for a long time when placed under perfectly dry conditions; and such conditions are, as a rule, more favourable to the formation of roots, both by stem and leaf cuttings, than any other. All that is necessary, when a stock of these plants is wanted, is to strip the leaves from the lower part of the stem, placing them on a dry shelf for a few days, and then laying them on pans or boxes of dry sandy soil in a warm house. This treatment causes the leaves to develop roots, and afterwards buds, which soon start into growth, when water may be given them in the same quantities as required by larger plants.
Pinguicula caudata.—This handsome Butterwort is propagated either from seeds, seldom ripened in this country, or by means of its large tongue-shaped leaves; it does not develop lateral or basal buds in the same way as the British Butterworts are known to do. The leaves require to be prepared as advised for Bertolonias, but a pan of silver sand should be used instead of soil for them. They should be inserted with their bases just in the sand, and the blade resting upon it. Over the pan a pane of glass may be placed, the whole to be stood on a shelf near the glass, in a stove temperature. If the sand is moist when the cuttings are inserted, little or no water will be required by the cuttings till buds are developed. Begonias may be treated as suggested for Gloxinias; or if to be propagated on a largo scale, a frame containing cocoa-nut fibre, heated to about 70°, may be used, pegging the Begonia-leaves on to the fibre. We may just refer here to the reproductive nature of some Fern-fronds, especially the Aspleniums, Nephrodiums, Aspidiums, and some Hymenophyllums, the fronds of which usually bear buds, which eventually form plants. The requirements of such leaves, when wanted for propagating purposes, are pretty much the same as those of the plants themselves.
Mention may also be made of the fleshy scales of some Cycads, of Marattias and Angiopteris, which have been employed as cuttings, owing to their power to root and produce plants. At Kew, both the Ferns here mentioned have been propagated in this way. The scales are large and succulent, and are borne on the stem about the bases of the leafstalks. When severed from the stem and placed in a propagating-frame, they first push forth roots, which are followed by the buds, generally a pair of buds to each scale, one on each side of the base.
The scales which form Lilium bulbs may, in like manner, be used for propagation, as if fresh when gathered, and placed in sandy soil in an intermediate temperature, they root and form small bulbs, capable of growing into large plants. All these exceptional ways of obtaining a stock of plants are only resorted to in rare cases; they are chiefly of physiological interest, showing, as they do, how nature has provided plants with auxiliary powers for their reproduction, which are held in reserve till called upon by the failure of the normal or proper means to fulfil the functions of increase or reproduction.