18 WOODWORKING - 



ter are more compact than the ones near the outside. The 

 center portion is called heart wood; the outer portion, sap 

 wood, because it conducts the sap which gives vitality to the 

 tree. 



Each ring, if observed closely, will be found to be made up 

 of two layers one denser than the other. These are called 

 annual rings because one pair of rings is formed each year. 

 The dense portion of the ring is the result of winter growth, 

 and the porous part is that formed in the spring and summer 

 when the growth is most rapid. 



Upon closer inspection, it will be observed that these rings 

 are crossed by radial lines running from the center to the bark. 

 These are called medullary rays. In a sense, they help to 

 bind the rings together. When cut at a slant, as they may be 

 in radial- or quarter-sawing, these rays, which are very solid, 

 will appear as light spots in the grain of the wood shown on 

 the surface of a board. The beauty of quarter-sawed wood 

 when polished makes certain kinds of it very desirable for in- 

 terior finish and furniture construction. One of the woods 

 which has this particular feature emphasized is oak. Other 

 grain irregularities, such as wanes and gnarls, make attractive 

 wood surfaces. Curly birch and bird's-eye maple are con- 

 spicuous examples. 



4. Seasoning. One of the most important parts of the 

 preparation of wood for construction use is its seasoning or 

 drying. A properly-seasoned board is lighter than one not 

 seasoned. It is stronger and is not subject to change of vol- 

 ume which causes checking and warping. Of the several 

 methods of seasoning, the best is natural-air-drying, which 

 takes from two to six years. In this process, boards are piled 



