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 bark. 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 
