Leaves, Buds, Blossoms, and Branches 65 



branch on which it grows. Some plants e.g., the pea 

 or apple have small, leaf like organs called stipules 

 growing at the base of the petiole. 



The function of a leaf. Animals eat food that is 

 already prepared for them, but plants must make their 

 own food from water and other materials that they get 

 from the soil and from the air. The leaves are the 

 organs that make the food. In the chapter on maples 

 you learned that sugar is formed in the leaves out of 

 water and .carbon dioxid (page 26). Sunlight supplies 

 the energy for this work. Without it the leaves could 

 not build up any food for the nourishment of the tree ; 

 a tree must therefore place its leaves so that the sun will 

 shine on them. Turn a potted plant that has been 

 standing near a window, halfway around. After a 

 day or two notice whether the leaves have changed their 

 positions. The leaves of trees as well as of other plants 

 are able to move to positions that will enable them 

 better to receive light, and the branches and twigs 

 grow so as to bring the leaves to the light. Moreover, 

 the leaves of each kind of tree have a definite arrange- 

 ment on the branches. The most common of these 

 arrangements are described below. Find an example 

 of each and see whether it prevents the leaves from being 

 shaded by other leaves on the same shoot. 



Two -ranked arrangement of leaves. Cut off a small 

 branch from an elm, with the twigs attached. Lay it 

 on a table, the floor, or the ground and notice that 

 without much pressure you can make every twig touch 

 the flat surface. See if you can do this with branches 

 irom other trees. Notice that on the elm the leaves 



