CELL-WALLS IN OIL AND MUCILAGE CELLS

The development and ultrastructure of cell walls of oil and mucilage c ells in selected representatives of so-called primitive and derived di cotyledons are summarized, and compared with information on cell walls in other idioblasts and secretory or protective tissues. Oil and muci lage cells of Cinnamomum and Annona, and presumably other Laurales and Magnoliales, are both characterized by a suberized layer deposited ag ainst the primary wall. These taxa usually do not form mucilage or oil cavities through fusion of secretory cells. Hibiscus and other Malval es lack such a suberized layer in their mucilage cells and as a rule h ave mucilage cavities, resulting from the breakdown of common walls be tween mucilage cells. The inner, polysaccharide wall deposited against the suberized wall layer in oil cells strongly resembles the first de posited, dense mucilage layer in mucilage cells; the precise compositi on of these wall layers requires further study. It is hypothesized tha t, as in certain crystalliferous cells, laticifers, secretory trichome s, and epithelial cells of resin ducts, the suberized layer in oil and mucilage cells serves to compartmentalize the secretion product. In e volution the suberized layer may have been lost in mucilage cells in p lant groups which possess exclusively mucilaginous secretory elements, and which are derived from ancestors with oil cells. However, an inde pendent, de novo (parallel) origin of mucilage cells (and cavities) wi thout suberized wall layers in derived and often unrelated dicotyledon ous families may have been an alternative evolutionary pathway.