LEAF-ARRANGEMENT. 109 



a Beech stem, it is obvious that there would be a 

 considerable waste of power. Once more, if the 

 leaves were parallel to the branch, they would, as 

 the branches are arranged, be less well disposed 

 with reference to light and air. A glance at Figs. 

 27, 28, 29, however, will show how beautifully the 

 leaves are adapted to their changed conditions. 

 The blades of the leaves of the upper pair form 

 an angle with the leaf-stalks, so as to assume a 

 horizontal position, or nearly so ; the leaf-stalks of 

 the second pair decussate with those of the first, 

 and are just so much longer as to bring up that 

 pair nearly or quite to a level with the first ; the 

 third pair decussate with the second, and are again 

 brought up nearly to the- same level, and immedi- 

 ately to the outside of the first pair. In well-grown 

 shoots there is often a fourth pair on the outside of 

 the second. If we look at such a cluster of leaves 

 directly from in front, we shall see that they gen- 

 erally appear somewhat to overlap ; but it must be 

 remembered that in temperate regions the sun is 

 never vertical. Moreover, while alternate leaves 

 are more convenient in such an arrangement as 

 that of the Beech, where there would be no room 

 for a second leaf, it is more suitable in such cases 

 as the Sycamores and Maples that the leaves should 



