108 



ESSENTIALS OF BOTANY 



the sun without cutting off too much light from other 

 leaves underneath. Such a leaf is in much less danger of 

 being torn by severe winds than are broader ones with 

 undivided margins. The same purposes are served by 

 compound leaves with very many small leaflets, such as 

 those of the honey-locust, mimosa acacia (Fig. 77), and 



Fig. 74. Opposite Leaves of Deutzia' (from the same shrub as Fig. 75), 

 as arranged on a Horizontal Branch. 



other trees and shrubs of the pea family. What kind of 

 shade is produced by a horse-chestnut or a maple tree 

 compared with that of a honey-locust or an acacia? 



127. Daily Movements of Leaves. — Many compound 

 leaves have the power of changing the position of their 

 leaflets to accommodate themselves to varying conditions 

 of light and temperature. Some plants have the power 

 of directing the leaves or leaflets edgewise towards the 

 sun during the hottest parts of the day, allowing them to 



1 Deutzia crenata. 



