The New International Encyclopædia/Alburnum
ALBUR′NUM (Lat. sap-wood, from albus, white). An old name for the sap-wood of ordinary trees (Dicotyledons and Conifers). As the tree adds new layers of wood, the ascending sap abandons the deeper seated layers, which also become modified through age. This leads usually to a sharp contrast in the appearance of the two regions, the outer region traversed by the sap (alburnum) being lighter in color and consisting of thinner-walled cells than does the older heart wood or “duramen.” See Wood.