CH. VII] THE LEAF. 95 



whose axils the eyes grow. Scale-leaves 

 again are what make the outer covering 

 of the buds of trees, they are familiar in 

 the horse-chestnut from their sticky outer 

 surface (see fig. 41). In the spring they 

 are seen unfolding and finally falling off 

 to allow the growth of the young branch, 

 i.e. the bud, shut up within them. The 

 markings on the surface of a horse-chest- 

 nut bough are instructive in connection 

 with both kinds of leaf. The most obvious 

 marks are broad triangular or shield shaped 

 depressions (L, fig. 42), which are the scars 

 left by the fall of the foliage-leaves in 

 former years : they occur in alternate pairs, 

 i.e. one pair of scars points N. and S., the 

 next E. and W. and so on. The scars are 

 marked near their lower border with a line 

 of dots or raised papillae 1 which are the 

 scars of the vascular bundles. When the 

 leaf was attached to the plant, the vascular 

 bundles ran from the leaf-stalk into the 

 branch, and when the leaf was cast in 

 autumn, the bundles were broken like the 

 rest of the tissues. At the upper edge 



1 Not to be confused with the lenticels scattered 

 irregularly over the bark. 



FIQ. 42. 



BRANCH OF HORSE CHESTNUT. 

 L, L, scars of fallen leaves. 

 W, W t wrinkled places where the scale-leaves of terminal buds once grew. 



