Germination

Germination, the sprouting of, a seed or other plant-germ. Thus the term is applied to the first starting in growth, after a period of rest, of the spores (q.v.) of fungi, or even of the grains of pollen (q.v.), the male germ of flowering plants. The requisite conditions for germination are moisture, a certain degree of warmth, and, in most cases, a supply of air or oxygen. In many spores and pollen-grains germination consists in the imbibition of water (or of a dilute solution of sugar) followed by the rupture of an outer spore-coat, or exospore, and the protrusion of the inner coat or endospore in finger-like or thread-like processes (hypha or pollen-tubes). In the more complex seed (q.v.), among flowering plants, the process begins similarly by the imbibition of water, the testa or outer seed-coat softening, and the whole seed swelling. The primary root (radicle) (or, in the case of most monocotyledons, the adventitious rootlets) then protrudes through the micropyle (a minute hole in the testa). This may be followed, especially in small exalbuminous seeds, by the withdrawal of the cotyledons or seed-leaves which then rise above ground, become green, and at once commence assimilation, the testa being often carried up by them as a mere husk; or, in the case of more fleshy or of albuminous seeds, the cotyledons may remain within the seed, or only their petiolar portion be withdrawn, the first leaves to rise above ground belonging to the plumule or primitive bud of the stem. The cotyledons in albuminous seeds feed in a quasi-parasitical manner upon the albumen, serving merely as channels to transfer its nutriment to the young root and shoot. The first-mentioned method of germination is termed epigeal - i.e. above ground; the other, hypogeal or under ground.