CHAPTEE X. 



Leaf Arrangement for Exposure to Sun and Air ; 

 Movements of Leaves and Shoots. 



122. 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 exposure 

 to the sun and air. This, 



J. 



Fig. 77. 



- Leaf Arrangement of the 

 Oak. 



Fig. 78. —Leaf Ar- 

 rangement of Euro- 

 pean Beech. 



in the vertical shoots of the elm, the. oak (Fig. 77), the apple, 

 beech, and other alternate-leaved trees, is not inconsistent 

 with their spiral arrangement of the leaves around the stem. 

 In horizontal twigs and branches of the elm, the beech (Fig. 

 78), 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. The 

 rows are produced, as it is easy to see on examining such a 



1 See Kerner and Oliver's Natural History of Plants, vol. I, pp. 396-424 



