BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VII. PLANT TISSUES

Secretory Tissues

Internal Secretory Tissues

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Fig. 53. Internal Secretory Tissues:

A - schizogenous receptacle in a St. John's wort leaf (1 - epithelium, 2 - secretion droplet); B - lysigenous receptacle in a mandarin peel; C - non-articulated laticifer of spurge; D - articulated laticifer of sow thistle.

Secretory Cells are interspersed among the Cells of the fundamental parenchyma. They contain resins, balsams, Essential Oils, Tannins, mucilages, Gums, salt crystals, etc. For instance, marshmallow roots contain mucilage cells and cells with calcium oxalate druses; valerian roots contain essential oils; while oak bark and snake-ROOT rhizome contain cells with tannins and calcium oxalate druses.

Secretory ducts are represented by two types: resin ducts (found in the stem of Scots pine, producing oleoresin) and oil ducts, found in the fruits of Apiaceae family members (dill, caraway, etc.), which secrete essential oils.

Receptacles can be schizogenous, lysigenous, and schizolysigenous.

This type of tissue is represented by individual secretory cells—secretory idioblasts, secretory ducts, receptacles, and laticifers (Fig. 53).

Schizogenous receptacles are formed by the accumulation of secreted substances in intercellular spaces. Such receptacles are surrounded by living epithelial cells. Examples of this group of receptacles include resin ducts, or canals, found in conifers, Asteraceae, Apiaceae, and other plants, where resinous substances and essential oils accumulate. Typically, resin canals are elongated and form a complex branching system. Unlike canals, receptacles are spherical in shape.

Lysigenous receptacles are formed in place of a group of cells that have disintegrated due to the accumulation of secretory substances within them. An example of such receptacles is the essential oil cavities found in the peel of citrus fruits.

Schizolysigenous receptacles are characteristic of eucalyptus leaves, where essential oil accumulates.

Laticifers are receptacles filled with latex, which exudes onto the surface when a plant is injured. Laticifers can be either non-articulated or articulated. They are located inside plant Organs among parenchymal cells, forming a complex network. Laticifer cells are living, with thin cellulosic walls and few pores. The protoplast forms a parietal layer and is multinucleate (in non-articulated laticifers) or uninucleate (in the segments of articulated laticifers), containing amyloplasts. The greater part of The Cell is occupied by a vacuole containing cell (latex) sap.

Non-articulated laticifers consist of a single giant tubular cell that can reach a length of several meters and form branches extending to all plant organs. They are characteristic of plants from the families Euphorbiaceae, Urticaceae, Apocynaceae, and Moraceae. A non-articulated laticifer cell originates in the seed embryo and subsequently expands and branches throughout all plant organs as the plant grows and undergoes Organogenesis.

Articulated laticifers consist of many sequentially connected cylindrical cells whose transverse walls break down, allowing their protoplasts and vacuoles with latex to form a continuous branched system. Such laticifers are found in plants belonging to the Asteraceae, Papaveraceae, Campanulaceae, and some Euphorbiaceae families. Articulated laticifers can interconnect via lateral tubules, forming anastomoses. Based on this feature, they are classified into anastomosing and non-anastomosing articulated laticifers. The type and Structure of laticifers serve as an important morphological and anatomical diagnostic feature in the microscopic examination of medicinal raw Materials.

At the end of the vegetative period, laticifers cease producing latex, flatten, die off, and their latex coagulates.

Latex is a white, yellow, reddish, brownish, or colorless liquid. It contains inorganic and organic substances with varying water solubility that form true solutions, as well as colloidal solutions, emulsions, or Suspensions.

The main component of latex is water (accounting for 50–82% of its content). In addition to water, it contains CARBOHYDRATES, organic acids and their salts, mineral salts, Alkaloids (mostly as salts of malic, citric, oxalic, succinic, and other acids), Glycosides, tannins, mucilages, fats, Proteins, Enzymes, and Terpenes. The latter group of organic substances is particularly interesting and diverse, including essential oils, resins, balsams, camphor, carotenoids, rubber, gutta-percha, etc.

Plants whose latex is rich in sugars, starch, inulin, fats, and proteins serve as good forage grasses (tragopogon, dandelion, lettuce).

In some members of the Asteraceae (kok-saghyz, tau-saghyz), Moraceae (ficus), and Euphorbiaceae (rubber tree, Hevea brasiliensis) families, the latex is rich in rubber and is referred to as latex, whereas in Celastraceae (spindle tree, Euonymus verrucosus), it is rich in gutta-percha. Natural rubber and gutta-percha are obtained from these plants.

The latex of alkaloid-bearing plants contains alkaloids. For example, cinchona bark contains quinine and 20 other alkaloids; the opium poppy contains over 20 alkaloids (including morphine, papaverine, and codeine), with the highest concentrations found in its seed capsules; and tobacco contains about 10 alkaloids. The alkaloid content in plants is influenced by growing conditions. A hot climate and nitrogen fertilizers promote alkaloid accumulation, which is why the vast majority of alkaloid-bearing plants grow in tropical countries. Plant latex may perform trophic, defensive, deterrent, or attractant Functions. The PRACTICAL USE OF latex is determined by its chemical composition.