20 Common Trees 



is girdled, the ring of cambium is severed. This kills the 

 tree, for the thin cambium layer is the life-giving part of 

 the stem. The most valuable part of a forest tree is the 

 stem, for in it is produced the wood that is used so exten- 

 sively by man. The principal functions of the stem are ( 1 ) 

 support of the tree crown; (2) transportation of food and 

 water; and (3) storage of food. During the winter months 

 considerable food is stored in the stem for use early in spring 

 when growth starts. 



The bark may be divided into two parts — the outer or 

 dry bark, and the inner or living bark. The bark of some 

 trees is very valuable. Some of their products are tannin, 

 cork, dye, and other important commercial products. The 

 bark is very helpful in identifying many of our common 

 trees. The beech can always be recognized by its smooth 

 gray bark, the shagbark hickory by its shaggy bark, and the 

 paper birch by its white bark which peels off in thin papery 

 scales. Other trees also have very distinctive features. 



The crown of a tree is made up of many parts such as 

 branches, twigs, buds, leaves, flowers, and fruit. The 

 branches and twigs have many markings, such as lenticels 

 (breathing pores) , leaf-scars, and bundle-scars, which are 

 helpful in recognizing trees. The buds are either opposite 

 or alternate in their arrangement. They are among the best 

 tree features to use for the identification of trees in winter. 

 In summer the leaves have the most distinctive characteristics. 

 In using them in tree identification work, it is helpful to 

 classify them into four major groups: (1) those with oppo- 

 site leaves; (2) those with alternate leaves; (3) those with 

 simple leaves; and (4) those with compound leaves. If 

 this simple clasification method is followed, tree identifica- 

 tion becomes easy and interesting. 



THE FOOD OF TREES 



WE KNOW that trees grow. They get bigger from year to 

 year. In order that they can grow they must feed. 

 The raw material out of which trees make their food comes 

 from two sources — the soil and the air. The rootlets with 

 their many small root-hairs absorb water and with it many 

 food substances are held in solution. During the growing 

 season there is a continuous flow of sap from the roots 

 through the stem to the leaves, where it is converted into 

 nutritious tree food. When the sunlight plays upon the 

 granules of leaf green, tree food is manufactured. To make 

 the food, water is brought from the stem through the leaf 

 stalks into the leaves. Then a complex chemical process takes 



