Propagating from cuttings is the mode employed in the production of certain species of trees, and when seed of other kinds cannot be readily obtained cuttings are used in their production. Though cuttings of some species of trees take a longer time to produce or emit roots than others, yet all kinds may be so propagated if allowed sufficient time for the formation of their roots. The root-producing substance, alburnum, or sap, partakes of the nature, in productive thrift, of the growth of which it is the life-blood; so it may be inferred that, according as the growth of the species is rapid or tardy, the period of perfecting of the roots may be determined.
Cuttings are detached branches or ends of branches of trees, usually from six to twelve inches in length, and are selected from shoots of the latest growth, though, in this case, if the tree is of considerable size and age, it will be necessary to select from the latest and lower shoots, and not from the main stem or first branches, as it has been decided that these latter participate in the age of the tree, while the later shoots bear age only from their year's origin; therefore this consideration is important as fixing the period of longevity of species propagated by cuttings. This peculiar characteristic may be accounted for from the fact of the yearly formation of sap-wood producing shoots which exist and thrive as part of itself, having birth as it were together, and increasing in size and strength proportionately -with the natural transformation of sap-wood to wood of compressed texture.
Cuttings of deciduous trees should be selected in the fall, and chosen from those limbs which are of apparent healthy vigor, tied in bundles and stored away till the following spring. The most convenient and safe way of preserving them during winter is by a covering of earth or other substance of sufficient depth to be out of the reach of frost. They should be cut smooth and square through the stem, and immediately under a bud, as this operation, when performed with nicety—care being taken not to crush the cutting in any of its parts— will facilitate the early production of the root, and prevent a hasty decay of the inserted end. There is an objection to the " slant cut," especially for cutting of trees or shrubs having a pith, as in them the absorption of water is great, and consequently the decay of the lower part of the cutting hastened.
When planted in the open ground, cuttings should be so placed uprightly to nearly their full length that only an inch or two of their tops will be visible above ground. They are usually planted in rows of two to four feet interval, and two to four inches between plants in the length of the row ; but the distance between plants will chiefly depend upon the object for which they are being raised.
Evergreens, being of a more tender nature than deciduous trees, require greater attention for their successful production, and are chiefly grown from seed, except when it becomes necessary to multiply or preserve a particular species or variety of species, in which instance they are propagated from cuttings or layers. They all, or nearly all, require artificial heat for their production, and for this reason are usually raised in hot-beds.
In the instance of cuttings of evergreens being placed under frame after selection in the fall, the debarring of the heating influence of the sun from them by shade becomes a necessity, so as to prevent an unseasonable or untimely growth of leaf, and allow for the prior development of the roots. This is owing to the decreased temperature requisite for the production of the root as compared with the warmth necessary for the growth of leaves.
The cuttings of evergreens are usually placed in rows, at six inches apart, and the soil firmly pressed about them to about one half their length, which is generally from two to three inches.