16 FARM FORESTRY 



c. Large saplings trees from 10 feet in height until 



they have reached a diameter of 4 inches 4^ feet 

 from the ground. 



d. Small poles trees from 4 to 8 inches in diameter. 



e. Large poles trees from 8 to 12 inches in diameter. 

 /. Standards trees from I to 2 feet in diameter. 



g. Veterans trees over 2 feet in diameter. 



The Structure of Wood. The roots, branches and stems 

 of trees are composed of wood. The structure of wood is not 

 simple like iron or gold, but like all organic material it is made 

 up of minute cells. These are somewhat similar in appearance 

 in cross section to the cells in honeycomb though many times 

 smaller. Usually they cannot be distinguished without the aid 

 of the magnifying glass. The walls of these cells are made up 

 of cellulose which is composed largely of carbon. In the living 

 state these cells are filled with a living substance called proto- 

 plasm. The cells are not all alike in wood even in the same 

 kind of tree, but differ in form and size and in the thickness of 

 cell walls. They also differ in their uses. Some cells conduct 

 food material to or from the crown, some store away reserve 

 food material until it is needed by the tree, some serve simply 

 to give strength to the woody tissue, while others have the 

 power of division into two or more cells and so produce growth 

 in trees. Water forms a large part of the wood of a growing 

 tree. Over half the weight will be composed of water chem- 

 ically combined, and in addition to this the tree will contain 

 from forty to sixty-five per cent of its dry weight of free 

 water. This free water largely evaporates when a tree is 

 cut, so that dry wood is much lighter in weight than green 

 wood. Well seasoned wood contains from ten to twelve per 

 cent of free water. 



The Parts of the Stem of a Tree. If the top of the stump 

 of a recently cut oak tree is examined, it will be found to be 

 made up of several parts. Around the outside will be ob- 



