A tree should usually be cut for timber at or near its maturity, as a young tree has too much sap-wood and will not be as strong and dense or durable, while an old one is likely to get brittle and inelastic and the centre of the heartwood is liable to decay, being the oldest portion. A young tree, though softer and not so durable, furnishes a tougher and more elastic wood, and sometimes has a finer grain.

Trees differ so much, and the uses to which the wood is to be put are so various, that no exact ages can be set for cutting - probably from fifty to one hundred years for good timber, to make a rough statement. Some trees furnish excellent timber at a much greater age than one hundred years. Pine is thought to be ripe for cutting at about seventy-five or one hundred years of ' age, oak at from sixty to one hundred years or more, and the various other woods mature at different ages.

Midwinter, or the dry season in tropical regions, is usually preferred for felling, because the sap is quiet. Decay sets in more rapidly in the sapwood and between the wood and the bark during the period of active growth, because of the perishable nature of the substances involved in the growth. Midsummer is considered equally good by some.

The various methods of cutting the log into the lumber of commerce have been treated in Chapter III (Wood)., to which the reader is referred. In this connection it will be noticed that, although boards cut through or near the middle are, as a rule, the best, when they contain the pith they are sometimes valueless in the centre, as well as when, in the case of an old tree, decay has begun at that point.

As the water evaporates gradually from green wood exposed to the air but protected from the weather, one might infer that in time it would evaporate entirely, leaving the wood absolutely dry, just as the water will entirely disappear from a tumbler or a teakettle. This is not so, however. The drying goes on until there is only about ten to twenty per cent, of moisture left, but no amount of open-air seasoning will entirely remove this small per cent, of moisture, the amount varying with the temperature and the humidity of the atmosphere. It can be got rid of only by applying heat, kiln-drying, baking, currents of hot air, vacuum process, or some artificial method of seasoning. After having completely dried the wood by any of these methods, if it is again exposed to the atmosphere, it absorbs moisture quite rapidly until it has taken up perhaps fifteen per cent., more or less, of its own weight. So you see that, though you may by artificial means make wood entirely dry, it will not stay in this unnatural condition unless in some way entirely protected from the atmosphere at once, but will reabsorb the moisture it has lost until it reaches a condition in harmony with the atmosphere. Recent investigations show that the very fibre or substance of the wood itself imbibes and holds moisture tenaciously, this being additional to the water popularly understood to be contained in the pores or cavities of the wood.

There are various other methods besides kiln-drying (referred to in Chapter III (Wood).) of seasoning and of hastening the drying process. Wood is sometimes soaked in water before being seasoned. This assists in removing the soluble elements of the sap, but it is doubtful whether the process improves the quality of the wood.

Smoking and steaming are also resorted to. Small pieces can readily be smoked, which hardens the wood and adds to its durability, - a method which has been known for centuries, - but care must be taken not to burn, scorch, or crack the wood.