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A FEW BOTANICAL NOTES FOR BEGINNERS.
A Perfect plant consists of the root, the trunk or stem, the leaves, the supports, the flower, and the fruit; for, hotanically speaking, by fruit (in herbs as well as in trees) is understood the whole formation of the seed.
I will begin by pointing out the uses of the root. The first and most obvious, is that of enabling the plant to stand firmly in the ground by serving as a balance to the head. By what means could enormous oaks be kept upright and fixed but by their extensive turgid roots ?—they serve as a counterpoise to the weight of the trunk and branches. The chief nourishment of the plant is received through the radicle or fibrous part of the roots that, like so many mouths, absorb the nutritious juices from the earth. The root also performs the part of a parent, by preserving the embryo plants in its bosom during the severity of winter, in form of bulbs or buds. Bulbs are properly only large buds, eyes, or germs, which include the future plants. Nature is an economist, and is sparing of this curious provision against the cold where it is unnecessary; therefore, in warm countries few plants are furnished with winter buds. Roots are distinguished by different names according to their forms, as fibrous, bulbous, and tuberous, with many other lesser distinctions expressive of their manner of growth.
The next part of a plant that claims our notice is the trunk or stem, which rises out of the root and supports the flower, leaves, &c The trunk of trees and shrubs (and it is supposed that the stem of the more diminutive kinds of plants likewise) consists of several distinct parts, as the bark, the wood, the sap-vessels corresponding to the blood-vessels in animals, the pith, the tracheae or air vesicles, and the web or tissue: each of these parts has its peculiar use, and its construction is admirably adapted to its purpose.
The bark of plants seems to perform the same offices for them that the skin does for animate; it clothes and defends them from injury, inhales the moisture of the air, and extracts or conveys from the plant the superfluity of moist particles. The fact of evergreens retaining their foliage during the winter is supposed to arise from an abundant quantity of oil in their barks, which preserves them from the effects of cold. The bark, as well as the wood, is supplied with innumerable vessels, which convey the fluids to and from every part of the plant; the wood is also furnished with others, which contain air and distribute it throughout the whole substance of the wood. The stability of trees and shrubs consists in the wood, which corresponds with the bones of animals.
The seat of life seems to reside in the pith or medullary substance, which is a fine tissue of vessels originating in the centre. The fluids of plants are the sap, analogous to the blood of animals, and the proper juice, which is of various colours and consistence in different individuals—white or milky in the dandelion, resinous in the fir, and producing gum in cherry or plum-trees, &c
The leaves contribute at the same time to the benefit and ornament of the plant. I need not tell you that the variety of their forms and manner of growth is great; your own observation must long since have informed you of this particular, and prepared you to understand the terms by which botanists arrange leaves, according to their forms and shapes, for example, simple, compound, rough, smooth, round, oval, heart-shaped, &c. Leaves are supposed to answer the purpose of lungs, and, by their inclination to be moved by the wind, in some degree serve also those of muscles and muscular motions. They are very porous on both surfaces, and inhale and exhale freely. The annual sunflower is an extraordinary instance of this fact—it is said to perspire, in twenty-four hours, nineteen times as much as a man. Fine weather encourages the perspiration of vegetables; but in heavy, moist, and wet weather the inhalation exceeds the exhalation in fine weather. The effluvia of plants is thought unwholesomo to persons of delicate constitutions, particularly at night and in a dull state of the atmosphere; but it is worth observing that the air emitted from the leaves is never harmful: that which is noxious proceeds from the corollas only.
The next parts to be considered are the supports or props. By these are meant certain external parts of plants which are useful to support them, or defend them from enemies and injuries, or for the secretion of some fluid that is baneful or disagreeable to those insects which would otherwise hurt them.
They are divided into seven kinds. 1st. Tendrils: small spiral strings by which some plants that are not strong enough to stand alone, sustain themselves by embracing trees, shrubs, or other support. The vine, pea, and bindweed afford examples of this class. 2ndly. Floral leaves: small leaves placed near the flower, smaller, and mostly of a different form from those of the plant. Srdly. Stipules: small leafy appendages situated on either side, or a little below the leaf, to protect it when first emerging from the bud. 4thly: Foot stalks. These support the leaf, and defend and convey nourishment to the infant bud. 5thly. Flower stalks, or foot stalks to the flower and fruit. 6thly. Arms: a general term for the offensive parts of plants, such as thorns, prickles, stings, ka. 7thly. Pubes: a name applied to the defensive parts of plants, such as hairs, wool, a certain hoary whiteness, hooks, bristles, glands, clamminess, and viscidity.
The viscous matter which surrounds the stalks under the flowers of the catchfly, prevents various insects from plundering the honey or devouring the pollen which fertilises the seed. In the dionsea muscipula, or Venus's fly-trap, there is a still more wonderful means of preventing the depredations of insects. The leaves are armed with long teeth like the antennae of insects, and lie spread upon the ground round the stem. They are so irritable, that when an insect creeps upon them they fold up and crush or pierce it to death. The sundew, a plant very common in our marshes, is likewise furnished with the same means of defence against its enemies. The flower of the arum muscivorum has the smell of carrion, which invites the flies to lay their eggs in the chamber of tho flower; but the worms which are hatched from these eggs are unable to make their escape from their prison, being prevented by the hairs pointing inwards; this has given the name of flyeater to this flower. The same purpose is effected in the dypsacus, commonly called teasel, by a basin or receptacle containing water placed round each joint of the stem.
The nauseous and pungent juices of some vegetables, and the fragrance of others, are bestowed upon them, in common with thorns and prickles, for their defence against the depredations of animals. Many trees and shrubs supply grateful food to a variety of creatures, and would be quickly devoured were they not armed with thorns and stings, which protect them not only against some kinds of insects, but also against the naked mouths of quadrupeds. It is worth remarking, as a farther analogy between plants and animals, that the former frequently lose their thorns, &c, by cultivation, as wild animals are deprived of their ferocity by living in a domestic state under the government and protection of man.
The Fructification includes the flower and fruit, and the