DAILY MOVEMENTS OF LEAVES 



97 



compound leaves with very 

 many small leaflets, such as 

 tjiose of the honey locust, the 

 mimosa, acacia (Fig. 108), and 

 other trees and shrubs of the 

 pea family. 



114. Daily movements of 

 leaves. Many compound 

 leaves have the power of 

 changing the position of their 

 leaflets to accommodate them- 

 selves to varying conditions of 

 light and temperature. Some FIG. 105. Opposite leaves of Deutzia, 



plants have the power of direct- as arranged on a vertical branch * 

 ing the leaves or leaflets edgewise towards the sun during the 

 hottest parts of the day, allowing them to extend their sur- 

 faces more nearly in a horizontal 

 direction during the cooler hours. 



The so-called "sleep" of plants 

 has long been known, but this sub- 

 ject has been most carefully studied 

 rather recently. The wood sorrel, 

 or oxalis, the common bean, clovers, 

 and the locust tree are some of the 

 most familiar of the plants whose 

 leaves assume decidedly different 

 positions at night from those which 

 they occupy during the day. Some- 

 times the leaflets rise at night, and 

 in many instances they drop, as in the red clover (Fig. 107) 

 and the acacia (Fig. 108). One useful purpose, at any rate, that 

 is served by the nocturnal position of the leaf is protection 

 from frost. It has been proved experimentally that when 



FIG. 106. Leaf mosaic of a 

 Campanula 



After Kerner 



1 It will be noticed that the exposure to sunlight is here not nearly as 

 favorable as in Fig. 104. 



