GROWING TREES 67 
turpentine from the pine, rubber from the rubber tree, 
and maple sugar from the maple tree. 
When a tree is cut down, a number of rings may be 
noticed across the stump. These are the annual rings, 
formed by periods of growth, each ring usually rep¬ 
resenting one year of growth. 
The Top of the tree is not so useful to man, but it 
is absolutely necessary for the tree. Those thousands of 
Fig. 44.—A spreading oak in the open country. 
leaves borne upon the oak are breathing organs. They 
take in carbon dioxide and give off oxygen. The green 
coloring matter, while the sun is shining, combines the 
carbon dioxide with water, making starches and sugars. 
Most of the food of a growing tree is manufactured in the 
leaves. 
Kinds of Trees.—Native trees found in many wood- 
lots are often of little value to the farmer. Most of the 
oaks may be used for making fence posts, but the Bois 
