THE EARTH'S BOUNTY 



" An annual layer once formed does not 

 change in size or place during the healthy life 

 of the tree, except that it is covered in time by 

 other, younger layers. A nail driven into a 

 tree six feet from the ground will still be at the 

 same height after it is buried under twenty or 

 fifty or one hundred layers of annual growth, 

 but in most trees, like the oaks and pines, 

 the wood becomes darker in color and harder 

 after it has been in the tree for some years, 

 the openings of its cells become choked, so 

 that the sap can no longer run through them. 

 From living sapwood, in which growth is go- 

 ing on, it becomes heartwood, which is dead, 

 because it has nothing to do with growth. It 

 is simply a strong framework which helps to 

 support the living parts of the tree. This is 

 why hollow trees may flourish and bear fruit. 



When the tree is cut down, the sapwood rots 

 more easily than the heartwood, because it 

 takes up water readily and contains plant food, 

 which decays very fast. Not all trees have 



heartwood, and in many the difference in color 



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