VEGETABLE. See BOTANY, PLANT, &c. A vegetable is composed of a root, stem, leaves, flowers, fruits, and seeds ; and when all these different parts are ful ly developed, the vegetable is said to be perfect. When any are deficient, or at least less obvious, the vegetable is said to be imperfect. The root is that part of the plant which is concealed in the earth, and which serves to convey nourishment to the whole plant. The stem, which commences at the termination of the root, bupports all the,other p arts of the plant. When the stem is large. and solid, as in trees, it is denominated the trunk, which is divided into the wood and the hark. The bark constitutes the outermost part of the tree, and covers the whole of the plant from the extremity of the roots to the termination of the branches. The bark is composed of three parts, namely, the epidermis, the parenchyma, and cor neal layers. The epidermis, which is a thin transparent membrane, forming the external covering of the hark, is compo sed of fibres crossing each other. When The epiderMis is removed, it is reproduc ed. The parenchyma, which is immedi ately below the epidermis, is of a dark green colour, composed of fibres crossing each other in all directions, and is RICCI}, lent and tender.
The cortical layers which constitute the interior part of the bark are compos ed of thin membranes, and increase in number with the age of the plant. The wood immediately under the bark is com posed of concentric layers, which increase with the age oldie plant, and may be se parated hit thinner layers, which, are composed of longitudinal fibres. The wood next the bark, which is softer and whiter, is called the alburnum The in. terior part of the trunk is browner and harder, and is denominated the perfect wood. • In the middle of the stem is the pith, which is a soft, spongy substance,, com posed of cells. In old wood this part en tirely disappears,t,and its place is occu pied by the perfect wood.
The leaves are composed of fibres ar ranged in the form of net-work, which proceed from the stem and footstalk, by which they are attached to the branches. These fibres form two layers in each leaf; which are destined to pertbrm different functions. The leaves are covered with the epidermis, which is common to the whole of the plant. Each surface,: of a leaf has a great number of pores and glands, which absorb or emit elastic fluids. .
are composed of different parts. The calyx or cup is formed by the exten sion of the epidermis ; the corolla is a Con. tinuation of the bark, and the stamina and pistilla, the internal parts of fructifica tion, are composed of the woody fibres and pith of the plant. Fruits are usually composed of a pulpy, parenchymatous substance, containing a great number of vesicles, and traversed by numerous ves sels. Seeds are constituted of the same utricular texture, in the vesicles of which is depositedsa pulverulent or mucous sub stance. These cells have a communica tion with the plants- by means of vessels, and by these is conveyed -the necessary nourishment during germination. .
Plants contain different orders of ves sels, which are distinguished from each other by their course, situation, and uses. Lymphatic vessels serve for the circulation of the sap- They are chiefly situated in the woody part of the plant. The pecu liar vessels which generally contain thick or coloured ilaids, are placed immediate ly under the hark ; they are smaller in number than the sap vessels, and have thin interstices filled up with utriculi or cells, with which they form a communi, cation. Some of theseproper vessels arc situated between the epidermis aid the bark, which are readily detected in the spring. Some are situated in the interior part of the bark, forming oval rings, and filled with the peculiar juices of the plaid. Another set of proper vessels is placed in the albu•nnm, nearer the centre of the stock or trunk, and sometimes in the perkct wood. The utriculi or cells constitute another set of vessels, which seem to resemble a flexible tube, slightly interrupted with ligatures at nearly equal distances, but still preserving a free cons municktion through its whole length. They vary in form, colour, and magnitude, in different vegetables, and exist in the roots, the bark, leaves, and flowers. The trachea, or spiral vessels, which are readi ly detected in succulent plants, appear in the form of fine.•threads, and may be drawn out to a considerable length with out breaking. These vessels are very numerous in all plants, especially under the bark, where they form a kind of ring, and are disposed in distinct bundles, in trees, shrubs, and stalks of herbaceous plants.