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, sometimes spreading over a considerable part of the seed, or nearly enclosing it, called an aril. A stro- 'pTiiole or caruncle is a similar appendage proceeding from the testa by the side of or 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 futui'e 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 difiicidt to distinguish imtil the seed begins to germinate. Their observation, however, is of the greatest importance, for it is chiefly upon the distinction between the embryo with one or with two cotyledons that are founded the two great classes of phsenogamous plants, Monocotyledons and Dicotyledons.
167. Although the embryo lies loose (unattached) within the seed, it is generally in some determhiate position with respect to the seed or to the whole fruit. This position is described by stating the direction of the radicla next to or more or less remote from the Jiiliim, or it is said to be superior if pointing towards the summit of the fruit, inferior if pointing towards the base of the fruit.
§ 15. Accessory Organs.
168. Under this name are included, in many elementary works, various external parts of plants which do not appear to act any essential part either in the vegetation or reproduction of the plant. They may be classed imder four heads : Tendrils and HooJcs, Tliorns and Prickles, Hairs, and Glands.
169. Tendrils (cirrhi) are usually abortive petioles, or abortive peduncles, or sometimes abortive ends of branches. They are simple or more or less branched, flexible, and coil more or less firmly round any objects within their reach, in order to support the plant to which they belong. Hooks are similar holdfasts, but of a firmer consistence, not branched, and less coiled.
170. Thorns and Prickles have been fancifully called the weapons of plants. A Thorn or Spine is the strongly pointed extremity of a branch, or abortive petiole, or abortive peduncle. A PricMe is a sharply pointed excrescence from the epidermis, and is usually produced on a branch, on the petiole or veins of a leaf, or on a peduncle, or even on the calyx or corolla. When the teeth of a leaf or the stipides are pungent, they are also c^Wed prickles, not thorns. A plant is spinous if it has thorns, aculeate if it has prickles.
171. Hairs, in the general sense, or the indumentum (or clothing) of a plant, in- clude all those productions of the epidermis which have, by a more or less appropriate comparison, been termed bristles, hairs, down, cotton, or wool.
172. Hau's are often branched. They are said to be attached by the centre, if parted from the base, and the forks spread along the surface in opposite directions ; ptlumose, if the branches are arranged along a common axis, as in a featlier ; stellate, if several branches radiate horizontally. These stellate hairs have sometimes their rays connected together at the base, forming little flat circular disks attached by the centre, and are then called scales, and the surface is said to be scaly or lepidote.
173. The Ejndermis, or outer skin, of an organ, as to its sui*face and indumentum, is
- smooth, when without any protuberance whatever.
- glabrous, when without hairs of any kind.
- striate, when marked with parallel longitudinal lines, either slightly raised or merely discoloured.
- furroii^ed (sulcate) or ribbed (costate) when the parallel lines are more distinctly raised.
- rugose, when wrinkled or marked with irregular raised or depressed lines.
- umbiiicate, when marked with a small roimd depression.
- umbonate, when bearing a small boss like that of a shield.