What is heart wood and sap wood ? Explain

Explanation

In most of the woody stems, the central older part of xylem becomes non-functional because older xylem tracheids and vessels become filled with resins, gummy or tannin-like substances produced by adjacent living parenchymatous cells. Their central non-functional xylem is called heart wood. On the other hand, the outer young and functional part of xylem is called sap wood.