§ 14. The Seed.

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161. The Seed is enclosed in the pericarp in the great majority of flowering plants, called therefore Angiosperms, or angiospermous plants. In Coniferæ and a very few allied genera, called Gymnosperms, or gymnospermous plants, the seed is naked, without any real pericarp. These truly gymnospermous plants must not be confounded with Labiatæ, Boragineæ, etc., which have also been falsely called gymnospermous, their small nuts having the appearance of seeds (158).

162. The seed when ripe contains an embryo or young plant, either filling or nearly filling the cavity, but not attached to the outer skin or the seed, or more or less immersed in a mealy, oily, fleshy, or horn-like substance, called the albumen or perisperm. The presence or absence of this albumen, that is, the distinction between albiminous and exalbuminous seeds, is one of great importance. The embyro or albumen can often only be found or distinguished when the seed is quite ripe, or sometimes only when it beings to germinate.

163. The shell of the seed consists usually of two separate coats. The outer coat, called the testa, is usually the principal one, and in most cases the only one attended to in descriptions. It may be hard and crustaceous, woody or bony, or thin and membranous (skin-like), dry, or rarely succulent. It is sometimes expanded into wings, or bears a tuft of hair, cotton, or wool, called a coma. The inner coat is called the tegmen.

164. The funicle is the stalk by which the seed is attached to the placenta. It is occasionally enlarged into a membranous, pulpy or fleshy appendage, sometime spreading over a considerable part of the seed, or nearly enclosing it, called an aril. A strophiole or caruncle is a similar appendage proceeding from the testa by the side of our near the funicle.

165. The hilum is the scar left on the seed where it separates from the funicle. The micropyle is a mark indicating the position of the foramen of the ovule (133).

166. The Embryo (162) consists of the Radicle or base of the future root, one or two Cotyledons or future seed-leaves, and the Plumule or future bud within the base of the cotyledons. In some seeds, especially where there is no albumen, these several parts are very conspicuous, in others they are very difficult to distinguish until the seed begins to germinate. There observation, however, is of the greatest importance, for it is chiefly upon the distinction between the embryo with one or two cotyledons that are found the two great classes of phænogamous plants, Monocotyledons and Dicotyledons. Cotyledons are said to be conduplicate when folded once lengthwise; contortuplicate when variously folded or twisted; conferruminate when so united that no line of separation can be traced.

167. Although the embryo lies loose (unattached) within the seed, it is generally in some determinate position with respect to the seed or to the whole fruit. This position is described by stating the direction of the radicle next to or more or less remote from the hilum, or it is said to be superior if pointing towards the summit of the fruit, inferior if pointing towards the base of the fruit.

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