LEAF EXPOSURE TO SUN AND AIR 



143 



FIG. 110. Opposite Leaves of Deutzia, as 

 arranged on a Vertical Branch. 



in the figure above mentioned) are found in the so-called 

 root-leaves of plants. Good examples of these are the 



dandelion, chicory, fall 

 dandelion, thistle, hawk- 

 weed, pyrola, plantain. 

 How are the leaves of 

 these plants kept from 

 shading each other? 



151. Much-Divided 

 Leaves. --Not infre- 

 quently leaves are cut 

 into slender fringe - like 

 divisions, as in the carrot, 

 tansy, southernwood, 

 wormwood, yarrow, dog- 

 fennel, cypress-vine, and many other common plants. This 

 kind of leaf seems to be adapted to offer considerable 

 surface to the sun without cut- 

 ting 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. 113), 

 and 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 ? 



FIG. 111. Leaf -Mosaic of a 

 Campanula. 



