176 ELEMENTARY FORESTRY. 



with wide annual rings are most durable, and are grown on the 

 low lands and in isolated positions. The wood of most broad- 

 leafed trees produced in the open is more durable than that from 

 the dense forest. 



Sound Mature Trees Yield More Durable Timber than 

 either young or very old trees. A tree is considered mature 

 when it ceases growing vigorously, which condition is indicated 

 by the flattening out of the crown, by dead branches in the 

 crown, and by changes in the color of the ba^rk. It is not indi- 

 cated by size, since this varies in the same species according to 

 circumstances. A small tree poorly situated for growth may be 

 as old or older than a larger tree growing under better condi- 

 tions. 



Intense Coloration of the Heartwood is a measure of 

 durability in timber, and faintly colored heartwood resembles 

 sapwood in its properties, only surpassing it in dryness. The 

 tannin or coloring matter of heartwood is antiseptic. Where 

 heartwood does not change its color or is lighter than the sap- 

 wood the protecting substances are generally absent, and the 

 wood is therefore liable to decay. This is plainly shown in the 

 hollow trunks of willow and basswood. 



Sapwood Contains More Ready-Made Food in forms 

 acceptable to a great number of kinds of fungi than the heart- 

 wood. This largely accounts for the fact that sapwood is much 

 more liable to decay than heartwood. This is especially true in 

 the case of Cedar and Pine, where the heartwood is protected by 

 resinous substances. But when the sapwood is well seasoned 

 and heavier than the heartwood it lasts as long. Wood that has 

 been once attacked by fungi becomes predisposed to further 

 decay. 



The Time of Cutting Timber affects its durability only as 

 the weather at the time of cutting affects the curing process. 

 Wood cut in summer is generally affected by decay-producing 

 fungi, rapid fermenting of sap, and by bad checking, owing to 

 very rapid curing on the outside. As the cracks thus made go 

 deep into the wood they may increase the danger from fungi. 

 Where summer-felled wood is worked up at once and protected 

 by kiln-drying, it lasts as long as that cut at any other season. 



Early winter is probably the best time to cut timber as 

 regards durability, since it then seasons slowly at a time when 



