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mals. Thus plants, in stoves and greenhouses, although they have sufficient heat and nourishment, are slender and weak, lose the colour of their leaves, and seem to languish for want of motion. And trees surrounded by high walls or buildings, and confined within narrow bounds, are slender, and grow tall, but not strong. From the observations, moreover, of some celebrated naturalists, a great similarity appears between the mechanism of plants and that of animals; the parts of the former bear some analogy to those of the latter; and the vegetable and animal economy appear to be formed on the same model.
The structure of plants is next to be considered. The roots, stalk, branches, leaves, flowers, and fruit, comprise all that is most remarkable in their external parts. The roots, by means of their different kinds of hinges, tuberosities, and ramifications, keep the plant fixed to the earth ; while their pores imbibe an exceedingly fine slime, which the water liquefies, and carries with it. From the root springs the stalk, to which the plant partly owes its strength and beauty. Being sometimes shaped Kke a pipe, the stalk is fortified by knots skilfully disposed. As it is sometimes too weak to support itself, it twists round a solid prop, fastening by means of the little hands with which it is furnished. In some it appears a strong pillar, rearing its proud head aloft in the air, and braving all the fury of storms and tempests.
The branches shoot forth like so many arms, from the trunk and stalk, on which they are distributed with great regularity. They are divided and subdivided into many small boughs; the subdivisions observing the same order as the principal divisions.
Thoseleaves, those charming ornaments of plants,
are disposed round the stalk and branches with the same symmetry. Some are simple, others compound, or formed of various foliage. One sort is plain, another indented. Some of them are very thin; others hard, soft, plump, smooth, rough, bairy, &c.
The flowers, whose beautiful enamel is one of the principal glories of Nature, are not less diversified than the leaves. Some have only a single leaf, or petal; others several. Here it appears like a large vessel gracefully opening: there it forms some grotesque figure, in imitation of a muzzle, head-piece, or cowl. Here it is a butterfly, a star, a crown, a radiant sun. Some are scattered on the plant without any art: some compose nosegays, globes, tufts of feathers, garlands, pyramids, &c. The greater part of them are furnished with a calyx; sometimes plain and simple; sometimes consisting of several pieces, or properly cut. From the centre of the flower proceeds one or more little pillars, called pistils, which are either smooth or channelled, rounded at top, or terminating in a point. These commonly encircle other smaller pillars, called stamina, which carry on the upper part of them a sort of small bladders, full of an exceedingly fine powder, called the pollen, or fertilizing dust; every grain of which, viewed through a microscope, appears of a very regular figure, but varied according to its species. In some they are small smooth globes ; in others they are thickly set with prickles, like the covering of a chesnut; and sometimes they resemble small prisms, or some other regular body. The flowers are succeeded by an infinite profusion of fruit and
· See No. XXVI. for an account of the Anatomy of Flowers, and the sexual system of plants.
AN fruits and seeds have this in common, that they inclose under one or more coverings the germ of the future plants. Some have only such coverings as immediately infold the germ, whose outside is of the strongest contexture; and, among these, there are some that are provided with wings, tufts, plumes of feathers, &c. by means of which they are conveyed in the air or water, so as to be transported and sown in different parts. Others are better clothed : being lodged in seeds or pods, inclosed in a kind of box, having one or more partitions. A third sort, under a delicious fruit, which is rendered still more agreeable by its beautiful colour, contain a stone and kernel. Others are inclosed in shells, which are either armed with prickles, abound with a bitter juice, or are adorned with a very fine down or hair. The outside of fruits and seeds, moreover, do not afford less variety than that of the leaves and flowers, there being scarcely any figure whaterer, of which they do not exhibit an exact representation.
Such are the exterior parts of plants: the internal are composed of four orders of vessels, namely, the ligneous fibres, the utriculi or little bags, the proper vases, and the tracheæ or air vessels.
The ligneous fibres are very small channels deposited according to the length of the plant, and consisting of little tubes placed near each other. Sometimes these vessels are parallel, and at others are separated, leaving between them intervals, or oblong spaces, which are filled by the utriculi, a kind of membraneous bladders, horizontally dis. posed, and communicating with each other. The proper vessels are a kind of ligneous fibres, that differ from the rest principally from their juice, which is of a deeper colour, or thicker.
In the middle of these, or round a great number of ligneous fibres, are some vessels, which are not so narrow, composed of a silvery elastic blade, formed spirewise, like a spring. These are arteries, and seldom contain any thing but air.
These four orders of vessels, which are dispersed through all the parts of the vegetable, in proportion to the nature and function of each, compose, at least in trees and shrubs, three principal and concentric beds, the bark, the wood, and the pith. The bark or rind, which is the outer covering, is smooth, even, and shining in some, and rough, chanelled and hairy in others : it is formed of the widest fibres, that are the least pressed together, and which admit within them the most air. The wood, which is placed under the rind, has, on the contrary, narrower and more contracted tubes. Its utricles are less replenished or dilated ; and this only has arteries. The pith, which is situate in the heart of the plant, is little more than a collection of utricles, which are greater and more capacious than those of the bark and wood.
From the structure of plants we proceed to their nutrition, by their roots and leaves. The saline, unctuous,' and subtile slime, which the water separates from the coarse earth, and keeps in a dissolved state, is the principal nutriment of plants. The different species of manure only contribute to the fertilizing of land, in proportion as they introduce into it a greater quantity of a spongy powder or active salt'.
After having been admitted into the body of the root by the extremity of the fibres, the nutritious juice rises into the ligneous fibres from the trunk or stalk, and passes into the utricles that adhere
· Şee No. XXIV. On the Food of Plants.
to them. It is there prepared and digested. It afterward enters into the proper vessels, under the form of a coloured fluid more or less thick, which we may conjecture to be with respect to the plant, what the chyle or blood is to the animal. Being filtered by the finer or more winding tubes, it is at last conveyed to all the parts, to which it unites, and increases their bulk.
The quantity of nutriment which a plant derives from the earth is in proportion to the number and size of its leaves; the smaller and fewer in number the leaves are, the less it draws.
The nutrition of vegetables is likewise effected immediately by their leaves. They not only serve for raising the sap, preparing it, and discharging its superfluity, but they are a kind of roots that pump from the air the juices they transmit to the neighbouring parts. The dew, which arises from the ground, is the principal foundation of this aërial nourishment. The leaves present to it their inferior surface, which is always furnished with an infinite number of small pipes that are always ready to absorb it. And that the leaves may receive no prejudice in the exercise of this function, they are dispersed with such art on the stalk and branches, that those which immediately precede, do not cover such as succeed them. Sometimes they are placed alternately on two opposite and parallel lines. Sometimes they are distributed by pairs, that cross each other at right angles. Sometimes they are ranged on the angles of polygons circumscribed on the branches, and so disposed, that the angles of the inferior polygon correspond with the sides of the superior. And sometimes the leaves ascend the whole length of the stalk and branches, in one or more parallel spiral lines.
By a mechanism, which is doubtless very sim