摘要：Culm sheath has always been considered a modified leaf. In this study, the anatomical structure of the culm sheath from Fargesia yunnanensis was analyzed to determine whether it originated from the foliage leaf blade or from the branch. The vascular bundles of the culm sheath showed greater similarity to the branches in shape and anatomical structure. In contrast to foliage blades, there are no midribs in culm sheaths. Stomatal density in the culm sheath is greater in the adaxial than it is in the abaxial epidermis, which is the opposite of that found in foliage leaf blades, and that density shows greater similarity to branches than it does to foliage blades. Fusoid cells are distributed on both sites of the vascular bundles in foliage blades, whereas culm sheaths have, instead, a few parenchyma cells that disintegrate and form air cavities when the sheath matures. Additionally, the culm sheath has no bulliform cells or trichome in its epidermis, and the shape of its long cells shows greater similarity to those of branches. Therefore, culm sheath is a modified branch, rather than a modified leaf.
