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.

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

CHAP. X.

OF PROPAGATION BY CUTTINGS.

THIS, which is the most common of all modes of artificial propagation except grafting, depends upon essentially the same principle as propagation by eyes; that is to say, the pieces of a plant called cuttings possess a power of growth in consequence of their bearing leaf-buds or eyes upon their surface. In striking by eyes, we have the great difficulty to encounter of keeping the eye active till it has organised roots with which to feed itself; the

earth furnishes such a supply unwillingly or unsuitably, nature intending that the bud should, in the first instance, be supported by the soluble nutriment ready prepared and lodged in its immediate vicinity, in the pith or some other part of the stem. For this reason, cuttings, which consist of eyes and the part containing their proper aliment, usually strike root more freely than eyes by themselves.

This being so, it is plain that a cutting is only capable of multiplying a plant when it bears buds upon its surface; and as the stem is the only part upon which buds certainly exist, so the stem is the only part from which cuttings should be prepared. And again, as the internode, or that space of the stem which intervenes between leaf and leaf, has no buds, their station being confined to the axil of

21

the leaves, a cutting prepared from an internode only is as improper as one from the root. It is no doubt true, that we constantly propagate plants from pieces of what are called roots, as in the Potato, or the Scirpus tube

rosus (fig. 21.); but such

roots are, in reality, the kind of stem called a tuber (51.): and, in like manner, other cases of

similar propagation are also successful, because the part called a root is, in reality, an underground stem covered with the rudiments of leaves, to each of which an eye belongs. The Rose, the Lilac, and many other plants have subterranean stems, cuttings of which will therefore answer the purpose of propagation. It will also occasionally happen, that, owing to unknown causes, morsels of the true root will generate what are called adventitious buds; and hence we do occasionally see the root employed for propagation, as in Cydonia japonica; but these are rare and exceptional cases, and by no means affect the general rule. Mr. Knight attempted to account for this, by supposing that the powers which roots of various forms, and cuttings, and other detached parts of plants, possess of emitting foliage, "are wholly, and in all cases, dependent upon the presence of true sap previously deposited within them." (Hort. Trans., v. 242.) But this is a very obscure expression, and does not seem to throw any light upon the subject.

When the Vine grows in a very warm damp stove, its stem emits roots into the air; the same thing happens to the Maize on the lower part of its stem; and in these and all such cases, the roots are found to be emitted from buds. Hence it has been inferred that the roots of a plant are as much productions of buds as branches are, and that

the stem is nothing more than a collection of such roots held together under the form of wood and bark. The present is not the place for a renewal of this discussion, for the arguments in favour of and opposed to which, the reader is referred to my Introduction to Botany, 3d edit. p. 309. &c. It is sufficient here, to remark that the question turns upon whether the buds and leaves actually themselves produce roots, or merely furnish the organisable matter out of which roots are formed; and that, therefore, for the purpose of horticulture, either the one or the other is equally capable of explaining the facts connected with cuttings.*

The following curious fact, recorded by Mr. Livingstone, which seems to have escaped observation, deserves to be mentioned here: — "The Pterocarpus Marsupium, one of the most beautiful of the large trees of the East Indies, and which grows in the greatest perfection about Malacca, affording, by its elegant wide-expanding boughs, and thick-spreading pinnated leaves, a shade equally delightful with the far-famed Tamarind tree, is readily propagated by cuttings of all sizes, if planted even after the pieces have been cut for many months, notwithstanding they appear quite dry, and fit only for the fire. I have witnessed some of three, four, five, six, and seven inches in diameter, and ten or twelve feet long, come to be fine trees in a few years. While watching the transformation of the log into the tree, I have been able to trace the progress of the radicles from the buds, which began to shoot from the upper part of the stump a few days after it had been placed in the ground, and marked their progress till they reached the earth. By elevating the bark, minute fibres are seen to descend contemporaneously as the bud shoots into a branch. In a few weeks these are seen to interlace each other. In less than two years the living