CHAPTER X 



LEAF ARRANGEMENT FOR EXPOSURE TO SUN AND AIR; 

 MOVEMENTS OF LEAVES AND SHOOTS 



149. Leaf Arrangement.^ — As has been learned from 

 the study of the leafy twigs examined, leaves are quite 



generally arranged so as to 

 secure the best possible ex- 

 posure to the sun and air. 

 This, in the vertical shoots 

 of the elm, the oak (Fig. 105), 

 the apple, beech, and other 

 alternate-leaved trees, is not 

 inconsistent with their spiral 

 arrangement of the leaves 



Fig. 105. — Leaf Arrangement 

 of the Oak. 



around the stem. In horizon- 

 tal twigs and branches of the 

 elm, the beech (Fig. 106), 

 the chestnut, the linden, and 

 many other trees and shrubs, 

 the desired effect is secured 

 by the arrangement of all the 

 leaves in two flat rows, one on each side of the twig.' 



Fig. 106. i- Leaf Arrangement of 

 European Beech, 



1 See Kemer and Oliver's Natural History of Mants, Vol. I, pp. 396-424. 



140 



