STEMS 69 



down the axis. Axillary buds may exist for several years 

 without any opportunity to develop, and they may even be 

 overlaid by the growth of the stem on which they stand. 



30. Scaly buds. The most conspicuous buds are the 

 so-called scaly buds, in which the outermost leaves develop 

 as dry and often hard scales, entirely unlike the true leaves 

 (Fig. 66). These overlapping scales protect the delicate 

 leaves within and the growing apex of the stem from sudden 

 changes of temperature and from moisture, and are often 

 made still more effective against moisture by becoming 

 covered with a sort of varnish or balsam, as in the horse- 

 chestnut and balsam-poplar. The inside of the scales or 

 the young leaves within are often covered with wool, as a 

 further protection against sudden changes of temperature. 

 It is evident that scaly buds are especially adapted to 

 protect delicate structures during the winter and early 

 spring, and hence are characteristic of the shrubs and trees 

 of temperate regions. 



In the spring, such buds first swell and then open, the 

 young branch emerging by the lengthening of its inter- 

 nodes, and gradually spreading its leaves. During the 

 opening the scales usually drop off, leaving more or less 

 complete rings of scars about the stem, thus permanently 

 marking the position of the bud. If a branch continues 

 to elongate for a number of years, its age and the amount 

 of growth each year can be determined by the successive 

 sets of bud scars. 



31. Naked buds. Buds in which no protective scales are 

 developed, or any other special coverings, are called naked 

 buds, and are characteristic of tropical plants, although 

 not entirely lacking in plants of the temperate regions. 



32. Accessory buds. In some plants more than one 

 bud may appear in the axil of a leaf, as in the maples, in 

 which three buds occur side by side (Fig. 67). As these 

 buds are most conspicuous in the early spring, the position 



