Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/107

branch becomes embedded and hardened among the woody

layers of the stem.

The mode in which branches come off from the stems gives rise to various forms of trees, as pyramidal, spread ing, or weeping, the angles being more or less acute or obtuse. In the Italian Poplar and Cypress the branches are erect, forming acute angles with the upper part of the stem ; in the Oak and Cedar they are spreading or patent, forming nearly a right angle ; in the Weeping Ash and Elm they come off at an obtuse angle ; while in the Weeping Wil low and Birch they are pendulous from their flexibility. The comparative length of the upper and under branches also gives rise to differences in the contour of trees, as seen in tho conical form of Spruce, and the umbrella-like form of the Italian Pine (Piuus Pinea). The branching of some trees is peculiar. In the Amazon district many Myris- ticaceai and Monimiaceae have verticillate branches coining off iu fives. This is also seen in the Chili Pine. Some Amazon trees taper downwards, so as to have a form like an inverted cone or pyramid, as in the Mulatto tree (Euky- lista Spruceana), one of the Cinchonacete.

Branches are sometimes long and slender, and run along the ground, producing buds with roots and leaves at their extremity or apex. This is seen in the runner (flagettum} of the Strawberry. Iu the Houseleek (Sempervivum) there is a similar prostrate branch of a shorter and thicker nature, producing a bud at its extremity capable of i .idependent existence. It receives the name of offset (propayaluni). In many instances the branch decays, and the young plant assumes a separate existence. Gardeners propagate plants by the process of layering, which consists iu bending a twig, fixing the central part of it into the ground, and, after the production of roots, cutting off its connection with the parent. A stolon differs from these in being a branch which curves towards the ground, and, on reaching a moist spot, takes root and forms an upright stem, and ultimately a separate plant. Tliis is a sort of natural layering, and the plant producing such branches is called stoloniferous. In the Rose and Mint a subterranean branch arises from the stem, which runs horizontally to a certain extent, and ultimately sends up an aerial stem, which becomes an independent plant. Such branches are denominated suckers, and the plants are surculose. The gardener divides the connection between tho sucker and the parent stem, in order to propagate these plants. In the case of Asparagus and other plants which have a perennial stem below ground, subterranean buds are annually produced, which appear above ground as shoots or branches covered with scales at first, and ultimately with true leaves. The young shoot is called a turio. These branches are herbaceous and perish annually, while the true stem remains below ground ready to send up fresh shoots next season. In Bananas and Plantains the apparent aerial stem is a shoot or leaf-bud sent up by an under ground stem, and perishes after ripening fruit. Branches are sometimes arrested in their development, and, in place of forming leaves, become transformed into spines or thorns, as in the Hawthorn. Plants which have spines in a wild state, as the Apple and Pear, often lose them when cultivated, in consequence of their being changed into branches ; in some cases, as in the Sloe (Prunus spinosa), (fig. 65), a branch bears leaves at its lower portion, and terminates in a spine. Plants bearing thorns (modifications of branches or leaves) are denominated spiny, spinose, or spinescent. A. bud is sometimes developed as a slender spiral or twisted branch, called a tendril or cirrus. In the Passion-flower the lateral buds are thus altered, with the view of enabling the plant to climb. In the Vine the tendrils are looked upon as the terminations of separate axes, or as transformed terminal buds, and are sometimes called sarmentri. In the Vine there are no young buds seen in the angle between the stem and leaves, nor between the stem and tendrils; and the latter are not axillary. Fig. 66 represents the branch of a Vine, in which a is the primary or first formed axis, ending in v, a tendril or altered terminal bud, and having a leaf / on one side. Between this leaf and the tendril, which represents the axis, a leaf -bud was formed at an early date, producing the secondary axis, or branch a", ending in a tendril v", with a lateral leaf /", from which a tertiary axis or branch a" was developed, ending in a tendril v ", and so on. The tendrils of Ampelopsis Veitchii are terminated by disks which secrete a sticky matter, by means of which they adhere to walls, &c. The tendrils, like those of the Vine, are modifications of the axis. Tendrils twist in a spiral manner, and enable the plants to rise into the air by twining round other plants. The direction of the spiral frequently differs from that of the climbing stem which produces the tendril. In the Vine the lower part of the stem is strong, and needs no additional support ; the tendrils therefore occur only in the upper part, where the branches are soft, and require aid to enable them to sup port the clusters of fruit. In the Bryony the tendril in the first part of its course twines from right to left, and in the last from left to right.

Fig. 65.

Fig. 66. FIG. 65. Branch of the Sloe (Prunus spinosa) producing spines or thorns which are abortive branches, as shown by their bearing leaves. FIG. Gfi. Portion of a branch of the Vine (Vitis rinifera), on which the terminal buds are converted into tendrils.

In some instances lateral buds are found without being in the axil of leaves. In this case they are extra-axillary. Such buds are produced after the stem and leaves have been formed, and in certain circumstances they are developed like normal buds. What have been called embryo-buds are woody nodules seen in the bark of the Beech, Elni, and other trees. They are partially, developed adventitious or abnormal buds, in which the woody matter is pressed upon by the surround ing tissue, and thus acquires a very hard and firm texture. When a section is made, they present woody circles arranged around a central pith, and traversed by medullary rays. The nodules sometimes form knots on the surface of the stem, at other times they appear as large excrescences, and in some cases twigs and leaves are produced by them.

Buds sometimes become extra-axillary in consequence

of the non-appearance or abortion of one or more leave.", or on account of the adhesion of the young branch to tho parent stem. In place of one bud there are occasionally several accessory ones produced in the axil, giving origin to numerous branches. Such an occurrence is traced to the presence of latent or adventitious buds. By tho

union of several such buds, branches are produced, having