I20 THE VEGETATIVE FUNCTIONS OF PLANTS 



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 {AJlsculus Hippocaslanum). 

 (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 



