Developmental anatomy of internal cavities of epidermal origin in leaves of Polygonum (Polygonaceae).

Two types of internal oil cavity that develop from the epidermis occur in leaves of 15 species of Polygonum, sect. Persicaria. In one type, found in 10 species, epidermal cells develop directly into epidermal/epithelial (E/E) cells. In P. hydropiper, a single protoderm cell enlarges, grows into the mesophyll, and divides only anticlinically to form three, to seven (usually four) E/E cells. The enlarging E/E cells separate along the medial pan of their shared walls to form a central cavity. The protoplast of each E/E cell then retracts from the inner cell wall and deposits a new cell wall to form a peripheral lacuna between the original inner wall and the new wall. The original cell walls between central cavity and peripheral lacunae eventually disappear leaving an oil-filled mature internal cavity but with each E/E tell tip still exposed at the surface. The second type, found m five species, involves both subepidermal and epidermal cells. In our examples. P. glabrum and P. densiflorum, the initial protoderm cell divides anticlinally to form 8-20 cells, most of which grow into the mesophyll, divide periclinally, and separate to become epithelial cells surrounding a cavity. The Outermost cells remain epidermal the deeper ones are secondarily subepidermal. Peripheral lacunae and a central cavity form as in the epidermal cavity, but they do not merge into a single mature cavity. Epithelial cells, peripheral lacunae, and central cavity collectively form a subepidermal cavity complex.