TYPES OF STEMS. 377 



be lateral to one another or they may be superposed as in the wal- 

 nut 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 axil- 

 lary buds fail to develop, this arrangement may be more or less 

 obscured. 



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 water-proof by 

 the excretion of resin between the scales or over the whole sur- 

 face. 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 recog- 

 nize 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. 



