CHAPTER II. 

 Stems and Branches. 



THE stem is the distinguishing characteristic of trees, 

 separating them from all other groups of plants. Although 

 in the region covered by this book the trees include all 

 the very large plants, size alone does not make a tree. 



A plant with a single trunk of woody structure that 

 does not branch for some distance above the ground, is 

 called a tree. Woody plants that branch directly above 

 the soil, even though they grow to the height of twenty 

 feet or more, are called shrubs, or, in popular language, 

 bushes. Many plants which have a tendency to grow into 

 the form of shrubs may, by pruning, be forced to grow 

 tree-like; some that are shrubs in the northern States are 

 trees further south. 



All the trees that grow wild, or can be cultivated out of 

 doors, in the northern States belong to one class, the stems 

 having a separable bark on the outside, a minute stem of 

 pith in the center, and, between these, wood in annual 

 layers. Such a stem is called exogenous (outside-growing), 

 because a new layer forms on the outside of the wood 

 each year. 



Another kind of tree-stem is found abundantly in the 

 tropics; one, the Palmetto, grows from South Carolina to 

 Florida. While in our region there are no trees of this 

 character, there are plants having this kind of stem, the 

 best illustration being the corn-stalk. In this case there 

 is no separable bark, and the woody substance is in threads 

 within the pithy material. In the corn-stalk the woody 

 threads are not very numerous, and the pith is very abun- 

 dant; in most of the tropical trees belonging to this group 

 the threads of wood are so numerous as to make the ma- 



