6 AMERICAN FOREST TREES 



no fundamental difference. The heart was once sapwood, and the latter 

 will sometime become heartwood if the tree lives long enough. As the 

 trunk increases in size and years, the wood near the heart dies. It no 

 longer has much to do with the life of the tree, except that it helps 

 support the weight of the trunk. The heartwood is, therefore, dead- 

 wood. The activities of tree life are no longer present. The color 

 changes, because mineral and chemical substances are deposited in the 

 wood and fill many of the cavities. That process begins at the center 

 of the trunk and works outward year by year, forming a pretty distinct 

 line between the living sapwood and the dead and inert heartwood. 



For some reason, the heartwood of certain species is prone to decay. 

 Sycamore is the best example. The largest trunks are generally hollow. 

 The heart has disappeared, leaving only the thin shell of sapwood, and 

 this is required not only to maintain the tree's life and activities, but to 

 support the trunk's weight. In most instances the substances deposited 

 in the heartwood, and associated with the coloring matter, tend to 

 preserve the wood from decay. For that reason heart timber lasts 

 longer than sap when exposed in damp situations. The dark and 

 variegated shades of the heartwood of some species give them their 

 chief value as cabinet and furniture material. The sapwood of black 

 walnut is not wanted by anybody, for it is light in color and is character- 

 less; but when the sap has changed to heart, and its tones have been 

 deepened by the accumulation of pigments, it becomes a choice material 

 for certain purposes. The same is true of many other timbers, notably 

 sweet and yellow birch, black cherry, and several of the oaks. 



It sometimes happens that when sapwood is transformed into heart, 

 a physical change, as well as a coloring process, affects it. Persimmon 

 and dogwood are examples, and hickory in a less degree. The sapwood 

 of persimmon and dogwood makes shuttles and golf heads, but after the 

 change to heartwood occurs, it is considered unsuitable. Handle 

 makers and the manufacturers of buggy spokes prefer hickory sapwood, 

 but use the red heartwood if it is the same weight as the sap. 



Annual Rings The trunks of both hardwoods and softwoods are 

 made up of concentric rings. In most instances the eye easily detects 

 them. They are more distinct in a freshly cut trunk than in weathered 

 wood, though in a few instances weathering accentuates rather than 

 obliterates them. A count of the rings gives the tree's age in years, each 

 ring being the growth of one year. An occasional exception should be 

 noted, as when accident checks the tree's growth in the middle of the 

 season, and the growth is later resumed. In that case, it may develop 

 two rings in one year. A severe frost late in spring after leaves have 

 started may produce that result; or defoliation by caterpillars in early 



