1Botany, (in some higher plants) a layer of cells surrounding the pith of the stem.
2Histology and Physiology= myelin sheath (now rare).
Early 19th century; earliest use found in Patrick Keith (1769–1840).
英汉双解词典包含464360条英汉词条，基本涵盖了全部常用单词的翻译及用法，是英语学习的有利工具。