12 FARM FORESTRY 



and its form more or less irregular or stunted. The root 

 systems of trees can be studied on those upturned by the 

 wind. 



The Trunk, Stem or Bole. The trunk of the tree sup- 

 ports and elevates the crown. It conveys water and salts ab- 

 sorbed by the roots to the crown and serves as a store house 

 for reserve food materials. The food manufactured by the 

 leaves in any year is not always completely used up in that 

 year for the growth of the tree or the ripening of fruit. 

 Usually more food is made than is needed. This excess of 

 food is stored in the tree over winter for use in the spring. 

 Seed years are brought about by the gradual accumulation of 

 reserve food materials in the tree. 



From an economic standpoint the stem is the most valuable 

 portion of a woodlot tree. On its size and shape depend the 

 amount and kinds of wood products such as lumber, cord wood 

 and posts that can be obtained. 



Each species of tree has its characteristic form of stem. 

 Some trees produce naturally a long, cylindrical stem free of 

 branches, while others develop a short, tapering stem more or 

 less branched or crooked. Trees grown in the open usually 

 branch low down forming a thick, short trunk. The same 

 kinds of trees grown in the forest produce long, cylindrical 

 trunks often free of branches for many feet. The bark cover- 

 ing the stem is also characteristic of each species of tree in 

 markings, thickness and color. It serves as a protection 

 against cold, heat, mechanical injury and the entrance of 

 insects and disease. It is impervious to the passage of liquids 

 and so prevents the sap leaving the tree freely through the 

 branches or stern. 



The Crown. The crown is usually the most conspicuous 

 part of the tree. It is composed of branches and leaves to- 

 gether with buds, flowers and fruit. Many life processes are 

 carried on in the crown. By their almost endless divisions 

 the branches enable the tree to present a large extent of leaf 



