Structure of mucilaginous epidermal cell walls in Passerina (Thymelaeaceae)

Leaves of Passerina are inversely ericoid. Adaxial epidermal cells are rela tively small, abaxial ones are large and tanniniferous. Mucilaginous epider mal cells are usually present in many Thymelaeaceae, including Passerina, m ainly in the abaxial epidermis. They are unequally divided by a periclinal wall-like septum into two separate compartments: (I) the outer, adjacent to the cuticle, containing mostly tanniniferous substances and (2) the inner, containing mucilage. This type of epidermis has often been incorrectly des cribed as uni-, bi- or multiseriate. Transmission electron microscopy revea led mucilage, characterized by microfibrils, embedded between the innermost wall-like septum and outermost layers of the inner periclinal cell wall. A s accumulation of mucilage increases, the innermost: (adjacent to the cell contents) layer of the original periclinal cell wall is pressed against the cytoplasm, thus forming a clearly demarcated cellulose periclinal wall whi ch divides the epidermis cell into two compartments, the inner with mucilag e and the outer comprising the cell lumen. Existing controversy is critical ly discussed. Our observations confirm the authenticity of mucilagination i n epidermal cell walls. (C) 1999 The Linnean Society of London.