Abstract
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.
Highlights
Sheath is an important morphological characteristic in Poaceae plants
Because there is a petiole between the foliage leaf blade and the leaf sheath, we considered whether the leaf sheath more likely originated from a branch rather than from a modified leaf
The vascular bundles in the culm sheath are composed of vessel elements and phloem and are surrounded by many fibre cells (Fig. 2a)
Summary
Sheath is an important morphological characteristic in Poaceae plants. In bamboo plants, there are three types of sheaths: the culm sheath (shoot sheath), the rhizome sheath and the leaf sheath. Wong[2] determined that all the leaf-like structures, including the rhizome sheath, culm sheath and branch sheath were homologous. It is because of their peculiar leaf-like shape that bamboo culm sheaths are considered modified leaves. Because there is a petiole between the foliage leaf blade and the leaf sheath, we considered whether the leaf sheath more likely originated from a branch rather than from a modified leaf. The anatomical characteristics of bamboo culm sheaths, sheath blades and foliage blades were observed and analyzed to draw distinguish them and to determine whether the culm sheath is a modified leaf or originated from a branch
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