The terms are much used in lumber transactions and are well understood by the trade. The two kinds of wood need be described only in the most general way, and for the guidance and information of those who are not familiar with them. Differences are many and radical in the relative size and appearance of the two kinds of wood in different species, and even between different trees of the same species. No general law is followed, except that the heartwood forms in the interior of the tree, and the sapwood in a band outside, next to the bark. In the majority of cases young trees have little heartwood, often none. It is a development attendant on age, yet age does not always produce it. Some mature trees have no heartwood, others very little. The two kinds of wood belong to needleleaf and broadleaf trees alike; but palms, owing to their manner of growth, have neither. Their size increases in height rather than in diameter. With palms, the oldest wood is in the base of the trunk, the newest in the top; but in the ordinary timber tree the oldest wood is in the center of the trunk, the youngest in the outside layers next the bark. It is the oldest that becomes heartwood, and it is, of course, in the center of the tree. The band of sapwood is of no certain thickness, but averages much thicker in some species than in others. The sapwood of Osage orange is scarcely half an inch thick, and in loblolly pine it may be six inches or more. Heartwood is known by its color. The eye can detect no other difference between it and the surrounding band of sapwood. There is no fundamental difference. The heart was once sapwood, and the latter will sometime become heartwood if the tree lives long enough. As the trunk increases in size and years, the wood near the heart dies. It no longer has much to do with the life of the tree, except that it helps support the weight of the trunk. The heartwood is, therefore, deadwood. The activities of tree life are no longer present. The color changes, because mineral and chemical substances are deposited in the wood and fill many of the cavities. That process begins at the center of the trunk and works outward year by year, forming a pretty distinct line between the living sapwood and the dead and inert heartwood.