What is the alburnum, or part of the wood on any exogenous tree next to the bark, being that portion of the tree through which the sap flows most freely; -- distinguished from Heartwood called?

sapwood — The alburnum, or part of the wood on any exogenous tree next to the bark, being that portion of the tree through which the sap flows most freely; -- distinguished from Heartwood. (Webster's 1913.)

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