Alburnum,

Alburnum, or SAP-WOOD, is the youngest and most external portion of the wood of ordinary dicotyledonous trees. It is still imperfectly hardened, and lies between the Bark (q.v.) and the heartwood or Duramen (q.v.). There is often a very marked division between it and the duramen, in trees whose age is such that the latter has been perfected. The alburnum differs from the duramen in having its tubes readily permeable by fluids (see SAP). It gradually hardens, and is transformed into duramen, new layers being added externally. It is almost always of a white or very pale colour, whilst in many trees the duramen is highly coloured. The alburnum is pale even in ebony, in which the duramen is black. In general, the alburnum is much inferior in value to the hardened or perfected wood. See TIMBER, WOOD.