LEAF EXPOSURE TO SUN AND AIR. 95 
leafy twig, by a twisting about of the petioles. The adjust- 
ment in the syringa, the maple, the horse-chestnut (Fig. 79), 
Fig. 80.— Leaf Arrangement of Horse-Chestnut on Vertical Shoots (side view). 
and many other opposite-leaved trees and shrubs, consists in 
having each pair of leaves cover the spaces between the 
