Cells or organizations of cells which produce a variety of secretions. The process of secretion is a separation of a substance from the protoplast of a cell. The secreted substance may remain deposited within the secretory cell itself or may be released from the cell. Substances may be secreted to the surface of the plant or into intercellular cavities or canals. Some of the many substances contained in the secretions are not further utilized by the plant (resins, rubber, tannins, and various crystals), while others take part in the functions of the plant (enzymes and hormones). Secretory structures range from single cells scattered among other kinds of cells to complex structures involving many cells; the latter are often called glands.