decomposition are presented to the plant, these are, animals, or vegetables, in a state of decomposition, or putrefaction.

Vital air, or oxygen gas, the other constituent part of atmospheric air, is neccessary to the respiration of man, and other animals, and this air is copiously emitted by vegetables: this renovation of the atmosphere being necessary to make up for the great consumption of it by respiration and combustion.

Hence arises a mutual and essential dependence of the animal and vegetable kingdoms upon each other. Animals, in breathing, consume the oxygen air, but return the nitrogen for the use of the vegetable; while the vegetable retains the nitrogen of the air, and the hydrogen of the water, for its own use, and returns the oxygen for ours. How admirable the designs of Providence, which make every different part of the creation thus contribute to the support and renovation of each other.

The carbonic air dispersed in the atmosphere, or in water, is also necessary to the vegetation of plants, in order to provide their carbonic principle, which is a constituent part of the fibres, oils, mucilage, and other vegetable principles. It is the basis of all vegetable matter. [See Note 2d, on Carbon-post.]

Buds of trees may be truly esteemed individual plants; and, if one of them be planted in the earth, with a cup inverted over it, to prevent its exhalation from being at first greater than its power of absorption, it will produce a tree similar to its parent.

Linnæus observes, that trees and shrubs are roots above ground; for, if a tree be inverted, leaves will grow from the root part, and roots from the trunk part.

Buds and bulbs are all annual productions, termed, by Linnæus, the hybernacula, or winter cradles of the plant. And Darwin observes, that the same term might properly be applied to seeds also.

Each bud has a leaf, which is its lungs, appropriated to it.

Leaves absorb carbonic acid gas, or fixed air, by their upper surface, and give out oxygen gas, or pure respirable air, by their under surface; as first discovered by Dr. Priestley.

Dr. Ingenhousz improved upon this discovery, by observing light to be necessary to these functions; remarking that in the dark, leaves give out a bad, or carbonic air, and that fruits and flowers almost invariably give out the last mentioned kind of air, at all times, but especially in the dark.

Virgil aludes to this noxious quality, in his tenth eclogue.

'But haste-unwholesome to the loitering swain "The shades are found

Ev'n Juniper's sweet shade, whom leaves around Fragrance diffuse, at eve are noxious found, Homeward, ye well fed Goats, now sinks the day, Lo, glittering Hesper comes! my Goats away!"

It has long been known that light acts beneficially upon the upper surface of leaves, and hurtfully upon their under side; and, if the latter be repeatedly turned to the light, or forcibly kept in such an unnatural position, the leaves grow sickly, black, or discoloured; as may be seen in plants trained against a wall.

Some leaves, if separated from their parent branch, and suspended by a slender thread, will turn their upper surface to the light, and vary their position, as the sun pursues his course. Sword-shaped leaves are an exception; they have no upper or under surface, but are vertical, and do not alter their position.

Light is considered as a stimulus or agent which decomposes the various nutritive principles, to be found in the air and water. It seems, in many instances, to be the sole cause of the expansion of flowers and leaves; for when it is withdrawn, they fold together and droop, as if dying; this has been elegantly termed by Linæus, 'the sleep of the plants;' and the Mimosa pudica, or sensitive plant, is a beautiful example of it. This plant, if kept in a dark room, for a considerable time, will require several minutes' exposure to the solar light before the stimulus of the light will dispose it to unfold, or expand its leaves.

Leaves always turn towards the light; this is necessary to the formation of their colour, as may be seen by the common practice of blanching celery, endive, &c. by covering them from the light; and by plants raised in darkness, which are of a sickly white.

Vegetables become destitute of smell as well as of colour, and lose much of their combustibility by growing in the dark. The celebrated Dr. Robertson, of Edinburgh, gives an account of a plant found in the drain of a coal-work under ground, which was very luxuriant, with large indented foliage, and perfectly white. He had not seen any thing like it, nor could any one inform him what it was. He had the plant with a sod brought into the open air in the light, when in a little time the leaves withered, and soon after new leaves began to spring up, of a green colour, and of a very different shape from that of the old ones. On rolling one of the leaves between his fingers, he found that it had the smell of common Tansy, and ultimately proved to be that plant, which had been so changed by growing in the dark. Indeed it was recollected,

that some soil had been taken into the drain from a neighbouring garden, some time before it was found so altered.

It has been ascertained, by experiment, that the green colour of vegetables may be produced by the light of a lamp, in the absence of the more perfect light of the sun; as discovered by the Abbe Tessier.

Leaves give out moisture by their under surface, in proportion to the intensity of light, and not of heat; so that there is scarcely any evaporation during the night. The water which exhales from vegetables is not pure, but serves as the vehicle of the aroma; it is equal to the third part of their weight every twenty-four hours, in healthy plants.

Leaves also expose the sap which they receive from the wood, to the action of the air, and return it again to the bark by its fibres or vessels. They also serve to nourish and prepare the buds of the future shoots, which are always formed at the base of the leaf stalk, and to shade them, as well as the fruit, from the too powerful heat of the sun. Hence it is, that in tropical countries the tree is never divested of the leaf.

Water is the only aliment which the root draws from the earth; and a plant can live and propagate itself, without any other assistance than the contact of water and air; as may be seen every day, in the Hyacinth, and other bulbous plants, which adorn our mantlepieces, as well as gramineous, or grassy plants, such as wheat, &c. raised in saucers or bottles, containing mere water.

In vegetables, hydrogen is the principle which fixes itself, while oxygen gas (the other constituent part of water) makes it escape.

But although pure water is more proper for vegetation, than water charged with salts, yet water may be disposed in a more favourable manner to the development of vegetables, by charging it with the remains of vegetable and animal decomposition: the plant then receives juices already assimilated to its nature. Independent of those juices already formed, the nitrogen gas (which has already been mentioned, as constituting one of the nutritive principles of plants) is abundantly afforded by the alteration of vegetables and animals, and must facilitate their development.

Although it has been proved, by various experiments, that pure water is sufficient to the support of plants, we must not, therefore consider the earth as of no use; it imbibes and retains water; it is the reservoir destined by nature to preserve the elementary juice which the plant continually requires; and to furnish that fluid in proportion to its wants, without exposing it to

the equally fatal alternatives of being either inundated, or dried up.

The nature of the soil must be varied accordingly as the plant requires a more or less considerable quantity of water, in a given time; and accordingly as its roots extend to a greater or less distance. Every kind of earth is not suitable for every plant; and, consequently a slip cannot be grafted, indifferently upon every species.

A proper soil is one which affords a sufficiently firm support to prevent the plant from being shaken; which permits the roots to extend themselves to a distance with ease; which becomes impregnated with humidity, and retains the water sufficiently, that the plant may not be without it when wanted.

To answer these several conditions, it is necessary to make a proper mixture of the primitive earths, for none of them in particular possesses them.

Silicious (white sand) and Calcareous (limy) may be considered as hot and drying; the Argillaceous (clayey) moist and cold; and the Magnesian (a primitive earth, having for its base a metallic substance, called Magnesium generally found in combination with other substances,) as possessing intermediate properties. Each, in particular, has its fault, which renders it unfit for culture; clay absorbs water, but does not communicate it; calcareous earth receives and gives it out quickly; but the properties of these earths are so happily opposed, that they correct each other by intermixture. Accordingly we find, that, by adding lime to an argillaceous earth, this last is divided; and the drying property of the lime is mitigated, at the same time that the stiffness of the clay is diminished.

Saline substances have been supposed of importance in vegetation by some, but they do not appear essential to the growth of any sort of plant except the Marine; such matters may, however, be of use to vegetation, though not essential to it. That of common salt may operate upon plants as it does upon the human body, by assisting to digest the food, without furnishing nutriment itself.

It is upon this principle, I presume, that common table salt mixed with water in a flower vase, will expedite the opening of a rose-bud, or other flower, when plucked from the parent branch.

Here I will observe, that if a small bit of nitre be added to the pure water, in a vase containing flowers; the water changed every day, and a small piece of the flower-stalk cut off each time of the change of water, the freshness of the flowers may be preserved for a considerable length of time.

Secretions. The sap, when exposed to the action of the air, light, and heat, by the leaves, becomes a new fluid, which assumes the peculiar flavour and qualities of the plant. Gum is one secretion, which oozes from the cherry, and other trees, resin and turpentine, are of the same nature; as is, also, the milky juice of the fig, poppy, &c. Almost all the fruit trees yield some sort of gum. And a species of the Acacia tree, in Arabia, yields the Gum Arabic, which is the chief nourishment of the nations of those parts, who obtain it in great quantities from incisions which they make in the trees. This Gum Arabic is now in frequent use in our own country; and forms a good aliment for young children; particularly when on a sea voyage, where milk cannot be commanded.

Another secretion is Caoutchouc, or Indian rubber, which is obtained from several species of trees in South America and the East Indies. The botanic names of the two species found in Cayenne, S. A. are Hævea caoutchouc and Jatropha elastica. The Ficus Elastica, of South America, is one of the principal trees from which the Caoutchouc is now procured. The fluid is collected from the tree by incision; the colour is, at first, a yellowish white, but, by exposure to the air, it becomes dark. Moulds made of clay, in the form of bottles, shoes, &c. are dipped into it repeatedly, and afterwards dried, and, when of a sufficient thickness, the clay moulds are easily crushed, and the pieces emptied

out.

The natives make vessels of it for containing water and other liquids; and, while soft, all sorts of designs are traced upon it. On account of its inflammability, it is used, at Cayenne, for torches. When warmed, it gives out a peculiar odour, but not an unpleasant one; from its smoke, a considerable quantity of very fine lamp black may be collected.

Rectified oil of turpentine, at common temperature, will afford a complete solution of it; and, when mixed with a solution of wax, in boiled linseed oil, it composes an elastic varnish, with which. they cover balloons; and which might be applied to a variety of useful purposes.

The fresh cut surface of the Caoutchouc will unite together by simple contact, and, by a proper pressure, may be brought so completely in union, as to be no more liable to separate in that part than any other.

The Caoutchouc, when cut in slips, and softened by immersion in boiling water, may be drawn out to seven or eight times its original length, and will afterwards, by its elasticity, resume very nearly its former dimensions. During its extension, a very sensible warmth is pro

duced, as may be discovered by applying it between the lips.

Another secretion to be found in every vegetable, in a greater or less degree, is sugar: but generally mixed with gum, sap, or other ingredients. It abounds most in fruits, and roots-as the beet, carrot, &c. but, more particularly in the Saccharum, or sugar cane.

The odour of plants, is a volatile oil of a resinous nature communicated to the surrounding atmosphere. This volatile oil is sometimes distributed through the whole plant, as in the Bohemia Angelica; sometimes it exists in the bark, as in Cinnamon. Balm and Mint contain their oils in the stem and leaves; Elicampane, and the Iris of Florence, in the root; Rosemary and Thyme in their leaves, and buds; Lavender, and the Rose, in the calyx of their flowers; Chamomile, Lemon and Orange Trees, in the petals. Many fruits contain it through their whole substance, such as Peppers, Juniper, &c. Oranges and Lemons, in the zest or peeling which encloses them, &c.

Fecula is the general name given to the farinaceous substance contained in all seeds, and in some roots-as Wheat, Indian corn, the Potato, Parsnip, &c. it is intended by Nature for the first aliment of the young plant.

Colour. The fixed colours of opaque bodies are, in all probability, owing to their absorbing some of the coloured parts of white light, or rays of the sun, and reflecting others; their immense variety arising from a mixture of the reflected primitive colours, in various number and proportion. It is impossible to say upon what cause the disposition of reflecting certain colours, in preference to others, may depend. The probability is, that it arises from the different textures of the surfaces.

There are some flowers, the petals of which are in different parts of the same leaf, of different colours; as of the Heart's Ease, for instance, which, if examined with a good microscope, will be found to have a different texture of the blue and yellow parts. The texture, also of the white and red Rose is very different.

It is from reflected rays that we judge of the colour of objects. The whiteness of paper, &c. is occasioned by its reflecting the greatest part of all the rays of light that fall upon it: the blackness of bodies, from their absorbing all the seven coloured rays.

The whiteness of the sun's light arises from the union of all the primitive colours. These primitive colours are, red, orange, yellow, green, blue, indigo, and violet; according to Sir Isaac Newton. Dr. Wollaston, who has performed many experiments on the refraction of light, in a more accurate manner than had been previously done, confines them to four colours only-red, green, blue and violet.

THERE are seven parts to a flower-the Calyx, Corolla, Stamens, Pistils, Pericarpium, Seed, and Receptacle.

The Calyx, sometimes called the flower cup, is formed of one or more green or yellow leaves, situated at a small distance from, or close to the blossom; its chief use is to support and protect the other parts of the flower; it is the envelope in which, in most cases, the tender flower lies, for a time, concealed, as the green leaves of a rosebud, which cover the blossom, and burst as the flower opens. In the rose, it is situated above the germen, or seed vessel; but, in the pea, it will be found beneath the seed vessel.

When remote from the flower, as in the Carrot and other umbelliferous plants, [See Note 3d-post] it is called an Involucre. When contiguous to the flower, or other parts of the fructification, as in the Primrose, &c. it is called a Perianth.

Some flowers have no Calyx, as the Tulip-others have them double, as in the Mallow; but most flowers have them single, as in the Primrose.

Linnæus considered the Calyx as a prolongation of the cortex, or outer bark of the plant.

Calyx.-The Perianth is not changed in double flowers; hence the genus, or family may be often discovered by the calyx.

The Corolla is formed by the delicate leaves called the blossom; as the red leaves of a rose, each one of which is called a Petal. It is distinguished from the Perianth by the fineness of its texture, and, generally, by the gayness of its colours. The corolla is considered the termination of the inner bark, or Liber.

The Stamens are threads within a flower, which have two parts: the filament, or slender part by which they are fastened to the flower; and the anther (which holds the pollen, or fine powder) situated on the top of the filament. They are seated externally with respect to the pistils, internally with respect to the calyx and corolla. They are inserted either into the calyx, the corolla, or the receptacle, rarely either upon the germen, or the style, Their number differs in different genera and species of flowers, from one to a hundred or more.

The Stamens, according to their number, situation, and proportion, furnish the leading principles of distinction in the artificial, or sexual, system of Linnæus. These organs are liable to be changed into petals, in what are termed double flowers; and, if the change be complete the flower will no longer bear a perfect seed.

Double flowers become what is botanically termed vegetable monsters, by the multiplication of their petals or nectaries.

In those flowers which have many petals, the lowest series of the petals remain unchanged in respect to number: hence, the natural number of the petals is easily discovered, as in poppies, roses, nigella, &c.

The Pistils are the threads situated in the centre of the flower; adhering to the fruit, for the reception of the pollen. A perfect pistil consists of three parts, the germen, style and stigma. The thickest part, at the bottom of the pistil, is called the germen, or seed-bud, and contains the rudiments of the young fruit, or seed; the style stands upon the germen, and serves to elevate the stigma or highest part of the pistil. The style is various in length and thickness, but not always present. The stigma, which is indispensably necessary, is, in some cases, seated immediately upon the germen. The shape of the stigma is either simple, being little more than a point; or it is capitate, like a pin's head, as in the Primrose. In most Grasses, the stigmas are amply branched or feathery, to detain the pollen. In the Mallow tribe, there is an abundance of viscid moisture evident in the stigand their rich purple or scarlet colour contrasts beautifully with the large yellow pollen, whose bursting, or explosion, may almost be seen with the naked eye.

ina,

The Pericarpium, or seed vessel is the germen grown to maturity. It varies extremely, being pulpy in apples, fleshy in cherries, juicy in gooseberries, and hard in nuts. In other words, the fruit which we eat, is nothing more than the pericarps, serving to protect the seeds till ripe.

The Seed is that part of every plant by which it is propagated. The part of the seed which contains the future plant is the germen vulgarly called the eye, no