sapwood n 1: newly formed outer wood lying between the cambium and the heartwood of a tree or woody plant; usually light colored; active in water conduction
Sapwood \Sap"wood`\, n. (Bot.) The alburnum, or part of the wood of any exogenous tree next to the bark, being that portion of the tree through which the sap flows most freely; -- distinguished from {heartwood}. [1913 Webster]