GLAND. In plants, a single cell or group of cells especially adapted to form and excrete some substances. Glandular cells are usually distin guished from others by the granular character of their protoplasm, especially when in the active state. Glands may be superficial or internal. Superficial glands may consist of a few cells or even a single cell, in which case they are often raised upon stalks and constitute the so-called glandular hairs, as upon the leaves of geraniums and primroses; they may have the form of disks upon short stalks, in which case the structure is known as a glandular scale; they may be groups of epidermal cells covering cushions of tissue, as in the so-called nectary (q.v.) in many flowers; they may be flush with the surface, pour ing their secretion into gland-lined pits or depres sions which may be narrow and deep or even branched canals, as in the nectar glands of some lily flowers. Internal glands in their simplest form consist of cells in which the secretion is formed and retained until released by the rup ture or crushing of the tissues, as in the gland cells of capers. Not uncommonly the gland-cells
are destroyed by the plant itself, in which case the freed secretion ochpies their place, as in the oil-glands of the orange and lemon rind; in other cases they line an internal spherical or tubular reservoir, into which the secretion is poured — as in the resin-tubes of pines (see figure).
Regarding the process of secretion nothing is definitely known. The secretion in most cases is formed by the protoplasm and within the cell wall; in others it may be developed at the sur face, the materials for it being secreted by the protoplasm. In superficial glands the secretion is sometimes pushed through the cell-wall as far as the cuticle. which it cannot penetrate, but which it lifts into a blister; e.g. the volatile oils secreted by many leaves.
Glands are named for the most prominent ma terial which they secrete, as water, lime, nectar, oil, and resin glands.