heartwood

noun

1. (countable, uncountable)The wood nearer the heart of a stem or branch, different in color from the sapwood.

   “A popular myth is that heartwood is stronger than sapwood.”

   “The staves are split from the heartwood. The heartwood is composed of dead cells; it supports the tree, but no longer has any physiological purpose. The staves must follow the grain of the wood to achieve a watertight cask, so they are split rather than sawn. — L'encyclopédie du Cognac: From log to stave”