=735. Buds occupying special positions.=—Several species of trees and shrubs produce more than one bud in each leaf-axil. The additional ones are termed accessory or supernumerary buds. These may be lateral to one another or they may be superposed as in the walnut or butternut. In such cases some of the buds usually contain simply floral shoots and are termed flower buds. In some species buds are frequently produced on the side of the branches and trunk at some distance from the leaf-axils, and entirely without regard for the latter; or more rarely may occur upon the root. Such buds are termed adventitious, and are the source of the feathery branchlets upon the trunks of the American elm. =736. Branching follows the phyllotaxy.=—Since the lateral or branch-producing buds are always located in the axil of a leaf, the branches necessarily follow the same arrangement upon the main axis as do the leaves. Since, however, many of the axillary buds fail to develop, this arrangement may be more or less obscured. [Illustration: Fig. 430. Bud of European elm in section, showing overlapping of scales.] =737. Coverings of winter buds.=—These are of two sorts, hair and cork, or scales. Buds protected simply by dense hair or sunk in the cork of the twig are termed naked buds, and are comparatively rare. Most species protect their buds by the addition of an imbricated covering of closely appressed scales, the whole frequently being rendered still more waterproof by the excretion of resin between the scales or over the whole surface. The scales when studied carefully are found to be much reduced leaves or parts of leaves. In some cases they represent a modified whole leaf, when they are said to be laminar, or a leaf-petiole, when they are petiolar, or stipular, when they are much-specialized stipules of a leaf which itself is usually absent. The latter type is much the less common. The form of the bud, the nature and form of the scales, when combined with characters furnished by the leaf- and bundle-scars, enable one to recognize and classify the winter twigs of the various woody species. =738. Phyllotaxy of the bud-scales.=—Since the bud-scales are leaves, they follow a definite phyllotaxy. This may or may not be the same as that of the foliage leaves. Twigs with opposite leaves have opposite bud-scales, or if with alternate leaves, then alternate bud-scales, but the fractions vary. If the scales are stipular, then there are of course two at each node.