The larch, from its lofty straight trunk and the high quality of its wood, is one of the most important of coniferous trees; its growth is extremely rapid, the stem attaining a large size in from sixty to eighty years, while the tree yields good useful timber at forty or fifty; it forms firm heartwood at an early age, and the sapwood is less perishable than that of the firs, rendering it more valuable in the young state.
The yellow pine is one of the most important timber trees of the genus; the heart-wood being very durable is largely employed in ship-building and for house timber, being nearly equal to that of P. sylvestris; large quantities are exported to Britain under the name of " New York yellow pine "; the sapwood is perishable.
It has light yellow sapwood and a brown heartwood.
Stumps thirty or forty years old, at least, will still be sound at the core, though the sapwood has all become vegetable mould, as appears by the scales of the thick bark forming a ring level with the earth four or five inches distant from the heart.
The key lies in the way in which growth rings change from being juvenile sapwood to becoming mature heartwood in later life.