AMERICAN FOREST TREES 13 



mon, and the best oak and elm. Among the softest species are buckeye, 

 basswood, cedar, redwood, some of the pines, spruce, hemlock, and 

 chestnut. 



The hardness of wood is tested with a machine which records the 

 pressure required to indent the surface. The condition of the specimen, 

 as to dryness, has much to do with its hardness. So many other factors 

 exercise influence that nothing less than an actual test will determine 

 the hardness of a sample. A table of figures can show it only approxi- 

 mately and by averages. 



Cleavability Wood users generally demand a material which does 

 not split easily, but the reverse is sometimes required. Rived staves 

 must come from timbers which split easily. Many handles are from 

 billets which are split hi rough form and are afterwards dressed to the 

 required size and shape. In these instances, splitting is preferable to 

 sawing, because a rived billet is free from cross grain. 



The cleavability of woods differs greatly. Some can scarcely be 

 split. Black gum is in that list, and sycamore to a less extent. Young 

 trees of some species split more readily than old, while with others, the 

 advantage is with the old. Young sycamore may generally be split 

 with ease, but old trunks seem to develop interlocked fibers which defy 

 the wedge. A white oak pole is hard to split, but the old tree yields 

 readily. Few woods are more easily split than chestnut. With most 

 timbers cleavage is easiest along the radial lines, that is, from the heart 

 to the bark. The flat sides of the medullary rays lie in that plane. 

 Cleavage along tangential lines is easy with some woods. The line of 

 cleavage follows the soft springwood. Green timber is generally, but 

 not always, more easily split than dry. As a rule, the more elastic a 

 wood is, the more readily it may be split. 



Durability In Egypt where climatic conditions are highly favor- 

 able, Lebanon cedar, North African acacia, East African persimmon, and 

 oriental sycamore have remained sound during three or four thousand 

 years. In the moist forests of the northwestern Pacific coast, an alder 

 log six or eight inches in diameter will decay through and through in a 

 single year. No wood is immune to decay if exposed to influences 

 which induce it, but some resist for long periods. Osage orange and 

 locust fence posts may stand half a century. Timber from which air 

 is excluded, as when deeply buried in wet earth or under water, 

 will last indefinitely; but if it is exposed to alternate dampness and 

 dryness, decay will destroy it in a few years. 



It is apparent that resistance to decay is not a property inherent in 

 the wood, but depends on circumstances. However, the ability to 

 resist decay varies greatly with different species, under similar circum- 



