Wood thus altered is known as heart-wood, or duramen, as distinguished from the young sap-wood, or alburnum, which, forming a cylinder next the cambium, remains alive and carries on the active functions of the xylem, particularly the conduction of water.
The sap-wood is made up of the outer layers or rings, and these are softer than the heart and generally of more open grain.
If the tree is too young the proportion of sap-wood is large, and the heart-wood is not so hard as that of a tree of mature age.
trees that have arrived at a mature age the heart-wood is in its largest proportion and the sap-wood is firm and elastic; and the timber from such trees is of the strongest, toughest and most durable character.
should be converted economical method, but, as will be seen in the diagram, the quality of the boards will vary very much, some consisting almost entirely of sap-wood cut at a tangent to the annular rings such as a, b, c, whilst the centre boards contain the heartwood cut in the best way at right angles across the annual rings as d, e, f.