"bundle sheath." YourDictionary, n.d. Web. 18 January 2019. <https://www.yourdictionary.com/bundle-sheath>.
bundle sheath. (n.d.). Retrieved January 18th, 2019, from https://www.yourdictionary.com/bundle-sheath
A layer or region of compactly arranged cells surrounding a vascular bundle in a plant. The bundle sheaths regulate the movement of substances between the vascular tissue and the parenchyma and, in leaves, protect the vascular tissue from exposure to air.