| a layer of cells in plant leaves and stems that surrounds a vascular bundle. |
| bundle sheath n. A layer or region of cells surrounding a vascular bundle. |
| 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. |