120 
in a resting state in buds. The outer coverings or scales 
of the bud are modified leaves or parts of leaves. They 
have almost or entirely lost their character as foliage 
organs, and while they are forming, their outer (dorsal) 
surfaces elongate more rapidly than their upper (ventral) 
surfaces. This causes them to curve together, so as to 
FIG. 79. Opening buds of horse-chestnut (Msculus Hippocastanum). 
(Cf. Fig. 80.) (Photo by E. M. Kittredge.) 
overlap, and form a protection to the embryonic stem, 
leaves, and other parts within the bud. With the return 
of warmth and moisture the following spring, the bud- 
scales resume their growth, but now their inner surfaces 
elongate more rapidly than their outer, reversing the 
method of their growth when forming. As a result of 
this, they begin to open outward. At the same time the 
