WOOD 



59 



Fig. 72. End of Log, showing 

 Annual Rings and Medul- 

 lary Rays 



By examining the end of a log we can learn a great 



deal of the life of the tree. It is made up of a number 



of irregular rings and of lines 



radiating from the center and 



running in nearly straight lines 



toward the bark. 



The number of rings tells us 



the age of the tree, as a new 



ring is added each year. 



As the tree grows, the old 



wood near the center becomes 



compressed and dry and is 



known as the heartwood, while 



that portion between the heartwood and bark is called 



sapwood. 



In some woods the dif- 

 ference between the 

 heartwood and sapwood 

 is very marked. In 

 ebony, for instance, the 

 heartwood is coal black 

 and the sapwood white. 

 The sketch shows half 

 a log, the annual rings 



being indicated, and also the radial lines, called medul- 

 lary rays. 



Fin. 73. Log cut lengthwise, showing 

 how " Grain " is formed 



