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 horsc- 
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 
