medullary sheath

noun

1. Botany. a narrow zone made up of the innermost layer of woody tissue immediately surrounding the pith in plants.
2. Anatomy. myelin sheath.

medullary sheath

noun

1. anatomy a myelin layer surrounding and insulating certain nerve fibres
2. a layer of thick-walled cells surrounding the pith of the stems of some higher plants

Word History and Origins

Origin of medullary sheath¹

First recorded in 1840–50

Example Sentences

Each one of the perforations is the entrance to an oblique tunnel, which is bored in the medullary sheath of the twig.

From Project Gutenberg

MS, medullary sheath, the dark, irregular ring just inside the bundles.

From Project Gutenberg