Cells or organizations of cells which produce a variety of secretions. The secreted substance may remain deposited within the secretory cell itself or may be excreted, that is, released from the cell. Substances may be excreted 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.
Epidermal hairs of many plants are secretory or glandular. Such hairs commonly have a head composed of one or more secretory cells borne on a stalk. The hair of a stinging needle is bulbous below and extends into a long, fine process above. If one touches the hair, its tip breaks off, the sharp edge penetrates the skin, and the poisonous secretion is released.Glands secreting a sugary liquid—the nectar—in flowers pollinated by insects are called nectaries. Nectaries may occur on the floral stalk or on any floral organ: sepal, petal, stamen, or ovary.
The hydathode structures discharge water—a phenomenon called guttation through openings in margins or tips of leaves.The water flows through the xylem to its endings in the leaf and then through the intercellular spaces of the hydathode tissue toward the openings in the epidermis. Strictly speaking, such hydathodes are not glands because they are passive with regard to the flow of water.
Some carnivorous plants have glands that produce secretionscapable of digesting insects and small animals. These glandsoccur on leaf parts modified as insect-trapping structures. Inthe sundews (Drosera) the traps bear stalked glands, calledtentacles. When an insect lights on the leaf, the tentacles benddown and cover the victim with a mucilaginous secretion, theenzymes of which digest the insect. See insectivorous plants.
Resin ducts are canals lined with secretory cells that releaseresins into the canal. Resin ducts are common in gymnospermsand occur in various tissues of roots, stems, leaves, andreproductive structures.
Gum ducts are similar to resin ducts and may contain resins,oils, and gums. Usually, the term gum duct is used withreference to the dicotyledons, although gum ducts also mayoccur in the gymnosperms.Oil ducts are intercellular canals whose secretory cells produceoils or similar substances. Such ducts may be seen, forexample, in various parts of the plant of the carrot family(Umbelliferae).Laticifers are cells or systems of cells containing latex, a milkyor clear, colored or colorless liquid. Latex occurs underpressure and exudes from the plant when the latter is cut.
These consist of thick walled, greatly elongated and much branched ducts containing a milky or yellowish colored juice known as latex. They contain numerous nuclei which lie embedded in the thin lining layer of protoplasm.They are irregularly distributed in the mass of parenchymatous cells.Laticiferous ducts, in which latex are found are again two types-
Also called as "non-articulate latex ducts", these ducts are independent units which extend as branched structures for long distances in the plant body.They originates as minute structures, elongate quickly and by repeated branching ramify in all directions but do not fuse together.Thus a network is not formed as in latex vessels.
Also called "articulate latex ducts", these ducts or vessels are the result of anastamosis of many cells.They grow more or less as parallel ducts which by means of branching and frequent anastomoses form a complex network.Latex vessels are commonly found in many angiosperm families Papaveraceae, Compositae, Euphorbiaceae, Moraceae, etc.
The function of laticiferous ducts is not clearly understood. They may also act as food storage organs or as reservoir of waste products, or as translocatory tissues.
See main article: Gland (botany).
This tissue consists of special structures; the glands. These glands contain some secretory or excretory products.A gland may consist of isolated cells or a small group of cells with or without a central cavity. They are of various kinds and may be internal or external.
Internal glands are
External glands are commonly short hairs tipped by glands. They are