The development of mucilage cells in Hibiscus schizopetalus

The development and (ultra-)structure of mucilage cells in the shoot apex and leaf in Hibiscus schizopetalus (Mast.) Hook.f. is described. In the shoot apex, mucilage cells mostly develop simultaneously in pairs. The mucilage was initially deposited as a layer between the plasma membrane and the cell wall. After prolonged mucilage deposition, the remaining cytoplasm was located in the centre of the cell, where it degenerated. At maturity, several mucilage cells arranged in one line, showed local breakdown of their common cell walls, and thus formed a canal or cavity which was surrounded by a sheath of smaller neighbouring cells. In the mesophyll, mucilage cells were present underneath the veins. The development was similar to that of mucilage cells in the shoot apex. Finally, several mucilage cells were aligned parallel to the vein and, after local cell-wall breakdown, fused with each other forming a kind of canal. Mucilage cells in the adaxial epidermis deposited mucilage against the inner, peripheral cell-wall. Upon prolonged mucilage deposition, the cytoplasm remained at the outer peripheral wall of the cells. In none of the mucilage cells of Hibiscus schizopetalus was a suberized layer detected in the cell wall. The differences between mucilage cells of the Malvaceae and those of the Lauraceae and Annonaceae are discussed.