TV ON PLANT LIFE 141 



which the twig can safely support, the length 

 also is determined. This argument is well 

 illustrated by comparing the leaves of the 

 Beech with those of the Spanish Chestnut. 

 The arrangement is similar, and the distance 

 between the buds being about the same, so is 

 the width of the leaves. But the terminal 

 branches of the Spanish Chestnut being much 

 stronger, the leaves can safely be heavier ; 

 hence the width being fixed, they grow in 

 length and assume the well-known and 

 peculiar sword-blade shape. 



In the Sycamores, Maples (Fig. 16), and 

 Horse-Chestnuts the arrangement is altogether 

 different. The shoots are stiff and upright 

 with leaves placed at right angles to the 

 branches instead of being parallel to them. 

 The leaves are in pairs and decussate with 

 one another ; while the lower ones have long 

 petioles which bring them almost to the level 

 of the upper pairs, the whole thus forming a 

 beautiful dome. 



For leaves arranged as in the Beech the 

 gentle swell at the base is admirably suited ; 

 but in a crown of leaves such as those of the 



