138 



OUR FORESTS 



Transportation of lumber in the East. Logs are mostly floated down rivers to the 



mills. 



our houses, for manufacture of furniture, wagon or car work, and 

 endless other purposes. 



Structure of Wood. — Quite a difference in color and structure is often 

 seen between the heartwood, composed of the dead walls of cells occupy- 

 ing the central part of the tree trunk, and the sapwood, the living part 



of the stem. In trees which are cut 

 down for use as lumber and in the 

 manufacture of various furniture, the 

 markings and differences in color are 

 not always easy to understand. 



Methods of cutting Timber. — A 



glance at the diagram of the sections 



of timber show us that a tree may be 



cut radially through the middle of 



the trunk or tangentiaUy to the 



ale middle portion. Most lumber is cut 



Diagrams of sections of timber: a, cross tangentially. Hence the yearly rings 



section ; h, radial ; c, tangential, take a more or less irregular course. 



(From Pinchot, U.S. Dept. of Agr.) The grain of wood is caused by the 



