Monocotyledons

Monocotyledons, the smaller and, in some respects, less highly organised of the two classes of angiospermous flowering plants. In their embryos they have only one cotyledon, which generally remains within the seed (hypogeal). The radicle does not usually, except in palms (q.v.), develop into a tap-root, often not even leaving the seed but being replaced by a tuft of adventitious, unbranched root-fibres. Bulbs, corms, and seldom-branched cylindric stems [Caudex] are common in this class. There are in the stem numerous closed fibrovascular bundles, i.e. strands of wood and bast (xylem and phloem), with no fascicular cambium (q.v.) or growing tissue between them, and, therefore, incapable of increase in diameter. The stems of a few arborescent forms are capable of indefinite increase in diameter, retaining a pericycle, or zone of merismatic fundamental tissue in which new bundles originate. This is the case in Draca-na and Aloe. There is neither distinct pith nor separable bark 10 the stem. The leaves are commonly simple, though often very large and sometimes tearing into leaflets, as in many palms. They are without stipules, often sheathing at the base, with a glossy smooth surface, entire or distantly toothed margin, and parallel main veins.

Much finer cross veins often divide the leaf into a regular network. The parts of the flower (q.v.) are generally in whorls of three, the typical floral diagram of the whole class being 3.3.3 + 3.(3). The seeds are generally albuminous. Some fossils apparently referable to Monocotyledons occur in Jurassic rocks; but the class is well represented for the first time in the Eocene. It is subdivided into two subclasses, Petaloideae and Nudiflorae, mainly by the characters of the perianth, which is petaloid in the one and reduced or absent in the other. The former is divided into the two series Hypogynce and Epigynce, according as the ovary is superior or inferior; and the latter into the Spadiciflora', which have a spadix (q.v.) or fleshy peduncle, and the Glumiflorce, in which the flowers are enclosed by rigid chaff-like bracts or glumes (q.v.). Among the chief orders of Monocotyledons are the Liliaceai, Juncaceai, Amaryllidacesc, Iridaceas, Orchidacea?, Palmacese, Aroidea?, Cyperaceaa, and Graminese, many of which are separately described.