PLANT LEAVES 



193 



the growing season, and from this the shoot continues to 

 grow the following season. Buds are also found along 

 the length of the stem and branches, as was seen in Ex- 

 periment 98. These are lateral buds and, since they are 

 usually found in the axis of the leaf, at the angle formed 

 by the leaf and stem, they are called axillary. In some 

 trees the terminal buds die at the end of the growing 

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

 axillary buds. 



94. 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 each other. 

 Their position generally 

 is such that the broad 

 upper surface of the leaf 

 receives the strong light 

 rays perpendicularly up- 

 on it. To accomplish 

 this, the leaves in many 

 trees are arranged spir- 

 ally 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, he 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. 



DIFFERENT FORMS WHICH LEAVES 

 ASSUME 



