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heartwood vs. sapwood

[hahrt-wood] / ˈhɑrtˌwʊd /

noun

  1. the hard central wood of the trunk of an exogenous tree; duramen.

[sap-wood] / ˈsæpˌwʊd /

noun

Botany.
  1. the softer part of the wood between the inner bark and the heartwood.