A region surrounding the small vascular bundles in the leaves of vascular plants. It usually consists of parenchyma cells but may sometimes consist largely of sclerenchyma. In angiosperms, the bundle sheath is a type of endodermis, which may be differentiated as a starch sheath. The cells of the bundle sheath have their long axes parallel to the direction of the vascular bundle. In dicotyledons, the parenchymatous bundle sheath is sometimes termed border parenchyma. Bundle sheath extensions, in which the cells of the bundle sheath extend to one or both epidermal layers, are present in many monocotyledons. They are believed to be concerned with conduction or support. See also Kranz structure. |
