heartwood

noun1

1. •
   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