DURABILITY OF WOOD. 231 



these fungi ; thej' may be pleasant, as those found some- 

 times in the Oak, or unpleasant as those infesting some 

 of the Poplars. Bj' studying both the favoiable and 

 the unfavorable conditions for the growth of the rot- 

 producing fungi, we may learn the best methods of 

 increasing the durability of our woods, and thus avoid 

 unnecessary waste. 



The soil and conditions imder which wood is grown 

 affects its durability. Coniferous v;oods with nar- 

 row, annual rings are most durable, especially wlien 

 grown on comparatively poor soils, in dense forests, and 

 at high altitudes. On the contrary, the hard woods 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 yoimg or very old trees. A tree is considered 

 mature when it ceases growing vigorously, which condi- 

 tion is indicated by the flattening out of the crown, by 

 dead branches in the crown, and by changes in the color 

 of the bark. It is not indicated 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 conditions. 



Intense Coloration of the Heartwood is a measure of 

 durability in timber, and fainth' colored heartwood re- 

 sembles 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 sapwood the protecting substances 

 are generally absent, and the wooct is therefore liable to 

 decay. This is plainly shown in the hollow trunlis of 

 Willow and Basswood. 



