PRINCIPLES.] HORTICULTURE 213 and their modes of disposition in different plants, on which see BOTANY, vol. iv. pp. 95-99, 118, 119, is a matter of the first consequence in the operations of pruning and training. Flower-buds may be produced on the old wood, i.e., the shoots of the past year s growth, or on a shoot of the present year. The pear and rhododendron develop flower- buds for the next season speedily after blossoming, and these may be stimulated into premature growth. The peculiar short stunted branches or " spurs " which bear the flower- buds of the pear, apple, and their allies, and of the laburnum, deserve special attention. In the rose, in which the flower- buds are developed at the ends of the young shoot of the year, we have an example of a plant destitute of flower- buds during the winter. Propagation by Buds. The detached leaf-buds (gemmae or bulbils) of some plants are capable under favourable con ditions of forming new plants. The edges of the leaves of Bryophyllum calycinum (see vol. iv. p. 98, fig. 67) and of Cardamine pratensix, and the axils of the leaves of Lilium bidbiferum (iv. 99, fig. 71), produce buds of this character. It is a matter of familiar observation that the ends of the shoots of brambles take root when bent down to the ground. In rare instances buds form on the roots, and may be used for purposes of propagation, as in the Japan quince. Of the tendency in buds to assume an independent existence gardeners avail themselves in the operations of striking " cuttings," and making layers and " pipings," as also in budding and grafting. In taking a slip or cutting the gardener removes from the parent plant one or more buds or " eyes," in the case of the vine one only, attached or not to a short shoot, and places them in a moist and sufficiently warm situation, where, as previously mentioned, undue evaporation from the surface of the leaf or leaves is prevented. For some cuttings pots filled with light soil, with the protection of the propagating house and of bell-glasses, are requisite ; but for many, such as willows, no such precautions are necessary, and the thrusting of the end of a shoot into moist ground suffices to -ensure its growth. In the case of the more delicate plants, the formation of roots is preceded by the production from the cambium of the cuttings of a succulent mass of tissue, the callus. It is important in some cases to retain on the cutting some of its leaves, so as to supply the requisite food for storage in the callus. In other cases, where the buds themselves contain a sufficiency of nutritive matter for the young growths, the retention of leaves is not necessary. In the tissues of willow-stakes just referred to there exists an abundance of material available for the supply of the young roots. The most successful mode of forming roots is to place the cuttings in a mild bottom-heat, which expedites their growth, even in the case of many hardy plants whose cuttings strike roots in the open soil. With some hard- wooded trees, as the common white-thorn, roots cannot be obtained without bottom-heat. It is a general rule through out plant culture that the activity of the roots shall be in advance of that of the leaves. Cuttings of deciduous trees and shrubs succeed best if planted early in autumn while the soil still retains the solar heat absorbed during summer. For evergreens April or May and August or September, and for greenhouse and stove-plants the spring and summer months, are the times most suitable for propa gation by cuttings. The great object to be attained is to secure the formation of active roots before the approach of winter. Layering consists simply in bending down a branch and keeping it in contact with or buried to a small depth in the soil until roots are formed ; the connexion with the parent plant may then be severed. Many plants can be far more easily propagated thus than by cuttings. Grafting or "working" consists in the transfer of a branch, the "graft" or "scion," from one plant to another, which latter is termed the "stock." The operation must be so performed that the growing tissues, or cambium-layer of the scion, may fit accurately to the corresponding layer of the stock. In budding, as with roses and peaches, a single bud only is implanted. Inarching is essentially the promotion of the union of one shoot to another of a different plant. The outer bark of each being removed, the two shoots are kept in contact by ligature until union is established, when the scion is completely severed from its original attachments. This operation is varied in detail according to the kind of plant to be propagated, but it is essential in all cases that the affinity between the two plants be near, that the union be neatly effected, and that the ratio as well as the season of growth of stock and scion be similar. The selection of suitable stocks is a matter still requir ing much scientific experiment. The object of grafting is to expedite and increase the formation of flowers and fruit. Strong-growing pears, for instance, are grafted on the quince stock in order to restrict their tendency to form " gross " shoots, and a superabundance of wood in place of flowers and fruit. Apples, for the same reason, are "worked" on the "paradise"or "doucin" stocks, which from their influence on the scion are known as dwarfing stocks. Scions from a tree which is weakly, or liable to injury by frosts, are strengthened by engrafting on robust stocks. Lindley has pointed out that, while in Persia, its native country, the peach is probably best grafted on the peach, or on its wild type the almond, in England, the summer tem perature of whose soil is much lower than that of Persia, it might be expected, as experience has proved, to be most successful on stocks of the native plum. The soil on which the stock grows is a point demand ing attention. From a careful series of experiments made in the Horticultural Society s Garden at Chiswick, it was I found that where the soil is loamy, or light and slightly | enriched with decayed vegetable matter, the apple suc ceeds best on the doucin stock, and the pear on the quince ; and where it is chalky it is preferable to graft the apple on the crab, and the pear on the wild pear. For the plum on loamy soils the plum, and on chalky and light soils the almond, are the most desirable stocks, and for the cherry on loamy or light rich soils the wild cherry, and on chalk the " mahaleb " stock. The form and especially the quality of fruit is more or less affected by the stock upon which it is grown. The Stanwick nectarine, so apt to crack and not to ripen when worked in the ordinary way, is said to be cured of these propensities by being first budded close to the ground, on a very strong-growing Magnum Bonum plum, worked on a Brussels stock, and by then budding the nectarine on the Magnum Bonum about a foot from the ground. The fruit of the pear is of a higher colour and smaller on the quince stock than on the wild pear; still more so on the medlar. On the mountain ash the pear becomes earlier. The effects produced by stock on scion, and more parti cularly by scion on stock, are as a rule with difficulty appreciable. Nevertheless, in exceptional cases modified growths, termed "graft-hybrids." n:lvP - hnr.n obtained whicL have been attributed to the commingling of the character istics of stock and scion. Of these the most remarkable example is Cytisus Adami, a tree which year after year produces some shoots, foliage, and flowers like those of the common laburnum, others like those of the very different looking dwarf shrub C. piirjmreus, and others again intermediate between these. We may hence infer that C. purpureuK was grafted or budded on the common laburnum,
and that the intermediate forms are the result of graft-
