GERMINATION

(Lat. germen.) The proce by which a plant is produced from a seed. The phaenomena of germination are best observed in dicotyledonous seeds; such, for instance, as the bean, pea, lupin, . These seeds consist of two lobes or cotyledons, enveloped in a common membrane; when this is removed a small projecting body is seen, which is that part of the germ which afterwards becomes the root, and is termed the radicle: the other portion of the germ is seen on carefully separating the cotyledons, and is termed the plumida; it afterwards forms the stem and leaves. When the ripe seed is removed from the parent plant it gradually dries, and may be iiept often for an indefinite period without undergoing any change; but if placed under circumstances favourable to its germination, it soon begins to grow.: these requisite circumstances are a due temperature, moisture, and the presence of air. The most favourable temperature is between 60° and 80°; at the freezing point none of the more perfect seeds vegetate; and at temperatures above 100°, the young germ is usually injured. No seed will grow without moisture: water is at first absorbed by the pores of the external covering, and decomposed; the seed gradually swells, its membranes burst, and the germ expands. The root is at first most rapidly developed, the materials for its growth being derived from the cotyledons; and when it shoots out its fibres or rootlets, these absorb nourishment from the soil, and the plumula is developed, rising upwards in a contrary direction to the root, and expanding into stem and leaves. For this growth the presence of air is requisite; if it be carefully excluded, though there be heat and moisture, yet the seed will not vegetate. Hence it is that seeds buried very deep in the earth, or in a stiff clay, remain inert; but, on admi ion of air by turning up the soil, begin to shoot forth. From experiments which have been made upon the germination of seeds in confined atmospheres, it appears that the oxygen set free by the decomposition of water combines with a portion of the carbon of the seed, and carries it off in the form of carbonic acid, and that the consequence of this is the conversion of part of the albumen and starch of the cotyledons into gum and sugar; so that most seeds, as we see in the conversion of barley into malt, become sweet during germination. Light is injurious to the growth of a seed. It is, therefore, obvious that the different requisites for germination are attained by placing a seed under the surface of the soil warmed by the sun's rays, when it is moistened by its humidity and by occasional showers; [s. 524]