LEAVES 



379 



and the next year's growth is due to one of the axillary 

 buds. 



Leaves. If we examine the arrangement of the leaves 

 on a plant or tree, we shall see that ,they do not lie one 

 directly above the other, but that they are so arranged as 

 not to shade one another. Their position generally is such 

 that the broad upper surface of the leaf receives the strong 

 light rays perpendicu- 

 larly upon it. To ac- 

 complish this, the leaves 

 in many trees are ar- 

 ranged spirally around 

 the stem. 



The stem of the leaf 

 itself, in some parts of 

 the tree, often grows 

 long and twists about, 

 in order to push the leaf 

 out to the light and yet 

 not let it be wrenched 

 away by the wind. The 

 horse-chestnut is such a 

 leaf. In some plants, 



like the sunflower, the younger leaves follow the sun all 

 day. In other plants the rays of the sun seem to be too 

 bright in the middle of the day and the leaves are then held 

 edgewise to the light. 



A striking example of this is the compass plant, the 

 leaves of which arrange themselves so that the sun's rays 

 strike the broad surface of the leaves in the evening and 

 morning when the rays are not very strong, but at noon the 



DIFFERENT FORMS WHICH LEAVES 

 ASSUME 



