Poplar (fig. 18. c), for which I am indebted to Sir Oswald Mosley; and although they have never yet been used for the purposes of propagation, except in the case of the Olive, there seems to be no reason why they should not be so employed, if any necessity were to arise for them. The real amount of their powers of growth is unknown, and would be a good subject of investigation.

CHAP. IX.

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.

Although this work was very absurd, yet it probably originated in the discovery that the 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 (53.) 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 (p. 152.): the power of Bryophyllum to do the same thing is familiar to every one. 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

See, also, DeCandolle's Physiologie Végétale, ii. 672.

by M. Neumann, chief gardener at the Garden of Plants at Paris, and of young Droseras furnished by the leaves of 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 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 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. 19.) produced a new 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

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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 ever

green 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 our gardens, we know of many other cases of the same kind. Hoya is a common instance, and three others are here figured (fig. 20.); viz., Gesnera (a), Clianthus puniceus (b), Gloxinia speciosa (c). In these, and all such cases, the first thing that happens is an excessive developement 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,