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BULLETIN 863, TJ. S. DEPARTMENT OF AGRICULTURE 



Topics for study. — The life of a tree and why it is necessary to 

 know something about how trees live. 



The leaves, trunk, and roots, and function of each in the tree's 

 existence. How the tree breathes and gets its food from the soil and 

 air; what travels upward and what downward in the branches and 

 stems. Structure of the leaf and different parts of the trunk. 



How the branches lengthen and the tree trunk increases in size; 

 the location, color, and structure of the living tissue or cambium 

 layer. What are annual rings, heartwood, and sapwood? 



Requirements for growth: Air, light, moisture, and heat. 



Trees in association — a stand. Influence of trees upon each other. 

 Difference, if any, between shape of crowns of open-grown trees and 

 those grown in close stands. Influence of different light and soil- 

 moisture supply. 



Fig. 15. — Effect of light supply upon the form and commercial value of trees. A, Elm which grew 

 up among other trees of the same height but since cut down. Clear trunks make valuable lumber. 

 B, This elm grew standing in the open. Trees with short limby trunks are useful chiefly as firewood 



• Effect of tree density (number of trees in a given area) upon 

 growth of the individual tree. Natural dying out of trees in close 

 stands with advancing age. Understocked, well-stocked, and over- 

 stocked stands and the production of (a) saw timber and (b) cord- 

 wood per acre under each condition. 



Practical exercises. — Make the following tests to show require- 

 ments for growth : Place a potted forest tree seedling in the dark 

 for a few days; withdraw moisture from one and supply moderate 

 amounts of moisture and excess moisture to other seedlings; sub- 

 ject plants, if possible, to different degrees of heat. Note results. 

 Erect a pole or 1 by 2 inch timber strip close beside a young, thrifty 

 sapling pine or hardwood. At regular intervals of a week or month, 

 mark on it the total height of the growing tree. Keep a record also 

 of the dates and measured heights. 



