Integuments

the external tissues that protect plants from unfavorable influences and perform the functions of absorption and excretion. Gas exchange between the plant and the environment occurs through the integuments. Primary integuments—epidermis and epiblem—arise from the protoderm, which consists of cells of primary meristem of the growing point of a stem or root. Exodermis becomes differentiated from the basal meristem of the growing point.

The epidermis covers the shoot, parts of the flower, the fruit, and the seed. Usually the outer walls of the epidermal cells of leaf and stem are thickened and impregnated with wax and cutin which, upon emerging to the cell surface, form the cuticle. Gas exchange and evaporation are accomplished through the stoma-tal apertures in the epidermis. The epiblem is formed just below the root apex, which is covered by the root cap. The cells of the epiblem absorb water and dissolved mineral matter from the soil; they also effect gas exchange and the excretion of metabolic products. The cells form root hairs, which significantly increase soil contact. After atrophy of the epiblem, the external cells of the primary cortex—the exodermis—take on a protective function. The primary integument is often replaced by a secondary one, or cork, which is a component of the periderm. The protective properties of cork are increased by the deposition of a sub-erin lamella on the internal surface of the cell membranes. Cork contains areas of loosely arranged cells known as lenticels, through which gas exchange and evaporation occur.

M. A. GULENKOVA