46 Trees, Stars, and Birds 



the sapwood. In black walnut, red cedar, and many 

 other trees, coloring matter deposited in the heartwood 

 makes it darker than the sapwood. The contrast in 

 most species is not so marked as in black walnut ; in 

 fir, spruce, and buckeye, the heartwood and sapwood 

 look much alike. In black locust, hardy catalpa, black 

 cherry, and several other species, the thickness of the 

 sapwood of old trees is usually less than an inch ; in 

 the hickory, elm, beech, and many other species, it is 

 several inches. In many species the dark-colored 

 heartwood is more valuable for furniture or interior 

 finish than sapwood from the same tree. 



Other differences in wood structure. One important 

 difference in different kinds of woods is in their medullary 

 or pith rays. These consist of thin- walled, brick-shaped 

 cells, whose principal function is to store nourishment 

 for future use. Some of the rays extend all the way 

 from the bark to the pith, while others which started 

 later do not reach all the way to the pith. They are 

 thin sheets of tissue that may be thought of as being 

 shaped like a ruler set on edge. When viewed from 

 the side they may, in woods like white oak, have a width 

 of an inch or even 4 or 5 inches. When their edges are 

 looked at, as in the end of a log or board, they are lines. 



In oak, beech, sycamore, maple, and cherry, the 

 larger pith rays are easy to see ; in many kinds of wood 

 they are so small that they can hardly be seen without 

 a lens ; in some species they are quite invisible unless 

 considerably magnified. Just how would you split a 

 section of a tree trunk to split it along the pith rays? 

 Is it easier to split wood along these rays or across them ? 



