34 



branches strive for the leadership but they are such close competitor* 

 that neither can win out. The result is a "stag-headed" tree. Again 

 a dormant bud may be stimulated into activity with the result that 

 no lateral branch obtains the leadership. After studying these 

 growth forms, one is inclined to think that the terminal shoot pre- 

 vents the erect growth of the lateral branches. 



Environment has a marked influence. The form of a tree growing 

 on an exposed mountain top differs very much from one growing on 

 sheltered bottomland. An open grown tree has a form entirely dif- 

 ferent from one grown in dense forest stand. The form of open 

 grown specimens varies with the species. Two different species 

 of Pine shown in Fig. 34 grew side by side in the same environment 

 and still developed entirely different crowns. Open grown trees 

 usually branch near the ground and have a broad, deep, symmetrical 

 crown, while trees grown in dense forest stand usually branch far- 

 ther from the ground and have a long clean trunk with a shallow and 

 often irregular and unsymmetrical crown. Trees grown in a dense 

 stand may not be so attractive as those grown in the open but they 

 yield a much higher grade of wood, since the lateral branches which 

 produce many of the knots in lumber are removed early in the life 

 history of the tree. The density of the forest stand should be so 

 regulated that on every acre of soil not only the greatest quantity 

 but also the best quality of wood is produced. 



Two kinds of branching are usually recognized, the excurrent or 

 upright and the deliquescent or spreading. When the main trunk 

 is continuous and extends upward to the tip without dividing it is 

 known as excurrent, and when the main trunk is not continuous but 

 divides and subdivides into more or less equal parts it is known as 

 deliquescent. Most of our evergreen species have the excurrent type 

 of branching, while most of our deciduous trees have the deliques- 

 cent type. A few of the latter, as the Pin Oak, Tulip Tree, and But- 

 tonwood, often show an excurrent or upright tendency in the form of 

 their trunk, especially when young. 



2. BARK : 



If we examine the growing point of a seedling we will find that 

 there is very little difference among the parts composing it. Soon, 

 as a result of growth, various kinds of tissue will be formed. At the 

 end of its first growing season we can differentiate roots, stem, and 

 leaves. The stem is still further distinguished into pith, wood, and 

 bark (Plate XI, 1.) Nature seems to know that the vital elementi 

 in the stem need protection. This protection is given by the bark. 



Bark is that portion of the stem which lies outside of the cam- 

 bium layer. It consists of an outer and an inner part. The former 

 is commonly known as the outer or dry bark and functions primarily 



