Germination of Seeds

Abstract

IN his Friday evening discourse at the Royal Institution on November 3 on “Germination of Seeds”, Sir Arthur Hill discussed the many ingenious devices for the protection of the seed and equally ingenious arrangements for the escape of the embryo on germination, which are found in plants. At one end of the scale are the plants, such as mangroves, the seeds of which germinate while still attached to the parent tree, the young seedlings dropping off into the mud. The great majority of seeds, however, have some sort of protective coat. Sometimes it is com-posed of the outer layer of the seed itself, as in the tomato, and sometimes of the inner layer of the surrounding fruit tissue, as in the plum and the cherry. In the former, under suitable conditions, the seed-coat becomes soft through absorption of water and the radicle emerges through the micropyle. In the second type, various devices have been evolved to allow of the escape of the seed or seeds enclosed in the hard inner wall of the fruit or endocarp. In the plum, the stone or endocarp splits into two halves, while in other cases a shutter-like valve is thrown off by the germinating seed. In the North American tupelos (Nyssa), there is one seed and one shutter, and from this type a series can be traced with an increasing number of seeds and corresponding shutters, to the case of Davidia, where there are seven or more seeds in each endocarp. Here the problem of overcrowding becomes acute, and many of the seedlings die. Other plants employ such devices as plugs or lids, for example, Hipparis, Hcemotostaphis, Dracontomelon, etc., which are thrown off, leaving a ‘window’ for the escape of the seedling. Here again, when there are many seeds, deaths occur owing to overcrowding, the extreme case of which is the Brazil nut, Bertholletia, where there are fifteen to twenty seeds enclosed in a hard woody fruit; as all germinate at once, only one of the ‘prisoners’ survives.