The sapwood of a tree; the pale, living outer wood layer that lies between the bark and the darker heartwood.
From Latin 'alburnum,' derived from 'albus' (white), literally 'white wood.' Used in botany and forestry since medieval times.
When you carve your initials into a tree, you're cutting through the alburnum—it's the living, water-conducting layer that will eventually harden into darker, dead heartwood as the tree ages.
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