CHAPTER IX.

OF PROPAGATION BY MERE LEAVES.

In the beginning of the last century, Richard Bradley, a Fellow of the Royal Society, published a translation from the Dutch of Agricola, of a book upon the propagation of plants by leaves, in which it was asserted that, by the aid of a mastic invented by the author, the leaves of any plant, dipped at the stalk end into this preparation, would immediately strike root; and the book was adorned with copperplates exhibiting both the process and its result, in the form of fields stuck full of Orange leaves growing into trees.

One of these plates illustrates, "How by means of fire and mummy, leaves, twigs, buds, and branches may be turned into shrubs and trees by planting them in the ground.'

"Having observed," he adds, "that the leaves of some plants may very well be used instead of joints or shoots, I shall now undertake to show how the leaves take root. The curiosity for cultivating vegetables, it is well known, has long since been carried so far as to occasion an attempt to raise a tree from a leaf, just as F. Mandirola made the experiment with a Lemon-tree-leaf. His words upon this subject, taken out of his writings, are as follows: 'I tryed a masterpiece, to wit, to plant Citron, Lemon, and such like leaves after the following manner. I took for that purpose a sort of little flower-pot full of the bestsifted earth; I planted in it some leaves of those kinds of trees, with their stalks so deep that the third part of the leaf was covered with earth; over that pot I fastened a small pitcher full of water, so as that it might drop directly down into the middle of the pot, and the hollow which was made by the falling of the drops I continually filled up with fresh earth: thus they cost me but a little trouble, and they all shot up and grew very well. I pursued it with the greatest patience in the world, and found that through a too often dropping of the water, the leaves began to rot, and so wasted away of themselves by little and

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MERE LEAVES PROPAGATE.

little, so that at last nothing was left but the stems; but it having been observed since, that from the callous matter that came forth at the bottom, both roots and branches shot out, it appears that all exotic leaves may at any time be converted into trees. For this operation I make choice of the months of July, August, and November; but those who have stoves and greenhouses may perform it even in winter, and in that case they shoot the better in the spring. Those who have a mind to do it in the spring will have some success; but it is not so very sure, which ought to be chiefly ascribed to the inconstancy of that season."

Although this work was absurd, yet it originated in the discovery that the mere leaves of some plants will grow under special circumstances; a fact often supposed to be much more rare than it really is. In Professor Morren's French translation of my Outlines of the First Principles of Horticulture, Rochea falcata is named as producing adventitious buds from the upper side of its leaves; and the Orange, the Aucuba, and the Fig, as other instances of leaves which will multiply their species the power of Bryophyllum to do the same thing is familiar to every one. Echeverias have been remarked to grow immediately from the leaves that naturally fall off even its flower-stalks. Hedwig found the leaves of the Crown Imperial, put into a plant press, produce bulbs from their surface. There is a well-known case of the same effect having been observed in Ornithogalum thyrsoideum. Mr. Auguste de St. Hilaire mentions an instance of leaf-buds generated by fragments of the leaves of "Theophrasta," which had been buried by M. Neumann, chief gardener at the Garden of Plants at Paris, and of young Drosera intermedia. Mr. Henry Cassini is said to have seen young plants produced by the leaves of Cardamine pratensis; English botanists know that offsets spring from the margins of the leaves of Malaxis paludosa; in our stoves we see Ferns of many kinds, especially Woodwardia radicans, propagating themselves by offsets from the leaves; Mr. Turpin tells us that floating fragments of Watercress leaves, cut up by a species of Phryganea for its nest, "produce presently from their base, and below the common petiole, at first two or three colourless roots, then in their centre a small

*

See, also, De Candolle's Physiologie Végétale, ii. 672.

SCALES PROPAGATE.

273

conical bud, green, in which are found, or rather from which successively arise, all the aërial parts of a new Watercress plant, while the roots multiply and lengthen." (Comptes rendus, 1839, sem. 2., 438.) Mr. Flourens also mentions a case of Purslane, whose leaves, divided into three, produced as

Fig. XXXVII.-Scale of Zamia sprouting.

many new plants, each having a root, stem, and leaves. In the Transactions of the Horticultural Society, is an account of a Zamia, each of whose scales (Fig. XXXVII.) produced a new

T

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INSTANCES OF LEAVES ROOTING.

plant, when the central part of the stem was decayed. Finally, the following case is named in the same work (vol. v. p. 242) by Mr. Knight :-" In an early part of the summer, some leaves of Mint (Mentha piperita), without any portion of the substance of the stems upon which they had grown, were planted in small pots, and subjected to artificial heat, under glass. They emitted roots, and lived more than twelve months, having assumed nearly the character of the leaves of evergreen trees; and upon the mould being turned out of the pots, it was found to be everywhere surrounded by just such an interwoven mass of roots, as would have been emitted by perfect plants of the same species. These roots presented the usual character of those organs, and consisted of medulla, alburnum, bark, and epidermis; and as the leaf itself, during the growth of these, increased greatly in weight, the evidence that it generated the true sap which was expended in their formation appears perfectly conclusive.”

In gardens, we have many other cases of the same kind. Hoya is a common instance, and three others are here figured (Fig. XXXVIII.); viz., Gesnera (a), Clianthus puniceus (b), Gloxinia speciosa (c). In these, and all such cases, the first thing that happens is an excessive development of cellular tissue, which forms a large convex "callus" at the base; from which, after a time, roots proceed; and by which eventually a leaf-bud, the commencement of a new stem, is generated.

It is not surprising that leaves should possess this quality when we remember that every leaf does the same thing naturally, while attached to the plant that bears it; that is to say, forms at its base a bud which is constantly axillary to itself. Leaves, however, have not been often employed as the means of propagating a species; and it is probable that most leaves, when separated from their parent, are incapable of doing so, for reasons which we are not as yet able to explain. The most common case of their employment is in the form of the scales of a bulb, which will, with some certainty, produce new plants under favourable circumstances. Those circumstances are, a strong bottom heat, moderate moisture, and a rich stimulating soil.

INSTANCES OF LEAVES ROOTING.

275

When plants are produced by leaves under ordinary circumstances, the conditions most favourable to their doing so are of

a

Fig. XXXVIII.-Rooting leaves of a, Gesnera; b, Clianthus puniceus; c, Gloxinia speciosa.

the same nature. A moderate amount of moisture prevents their dying from perspiration or perishing from decay; a good bottom heat stimulates their vital forces, and causes them to exercise whatever power they possess; and, in addition, they are covered by a slightly shaded bell-glass, which maintains around them an atmosphere of uniform humidity, and, at the same time, cuts off the approach of those direct solar rays, which, acting as a stimulus to perspiration, would have a tendency to exhaust the leaves of their fluid before they could organise, at their base, the new matter from which the leaf-bud is eventually produced.

The rationale of this operation seems to be as follows.