54 THE TREE AND ITS CHARACTERISTICS 



4. Standards from 1 foot to 2 feet in diameter at 4% feet above 



ground. 



5. Veterans over 2 feet in diameter at 4% feet above ground. 



2. HOW A TREE FUNCTIONS 



A tree is a living organism, complex in its structure, and not 

 entirely understood as yet as to its functions. 



A tree has three parts, each of which performs a distinct function 

 in its life. They may be described as follows: 



? 



1. The roots furnish water and nourishment/ and hold the tree in 



place against the elements of nature, such as wind, storms, ice, and 

 snow. The older roots are most useful in holding the tree in place. 

 The young roots or tendrils have the power of assimilating and taking 

 up water and nourishment. The root system of a tree is generally 

 within 3 to 5 feet of the top soil and in young trees within 1 or 2 feet. 

 In early life, some trees have taproots as in oaks and walnuts, but 

 none of the trees in later life have a deep taproot which enters many 

 feet into the earth. A well-developed root system is very important 

 in planting even more important than the crown. 



2. The stem, known also as the trunk or bole, furnishes wood for 

 mankind, conducts water and food to the leaves, and provides support 

 to the crown. The main trunk consists of bark, sapwood, and heart- 

 wood. Bark serves as a protective cover to the cambium layer which 

 is found between the inner bark and the sapwood. This is the region 

 of expansion and growth. A new layer of wood is added each year. 

 Sapwood is the living portion of the wood next to the bark. It con- 

 tains considerable plant food and has a higher moisture content than 

 the heartwood. It is more susceptible to insect and fungus attacks 

 and generally is lighter in color and weight. The heartwood forms 

 the center of the trunk and usually a very large proportion of it ex- 

 cept in young trees. It is physiologically dead and performs only the 

 function of support. It is much harder, darker in color, more durable, 

 and ordinarily more valuable than the sapwood. 



3. The crown consists of the branches, twigs, leaves, flowers, and 

 fruit. The leaves serve the tree as the lungs do men. Carbon dioxide 

 in the air enters the leaves and, under the action of light, air, and 

 water, performs certain life functions resulting in the formation of the 

 annual layer of wood on the trunk, roots, and branches. Oxygen is 

 given off from the leaves, and the carbon is retained. This combined 

 with water obtained from the roots forms starch, sugar, gum, and 



