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decomposition are presented to the plant, these are, But haste—unwho.esome to the loitering swain
Ev’n Juniper's sweet shade, whom leaves around
It has long been known that light acts beneficially of it by respiration and combustion.
upon the upper surface of leaves, and hurtfully upon their Hence arises a mutual and essential dependence of
under side; and, if the latter be repeatedly turned to the the animal and vegetable kingdoms upon each other.
light, or forcibly kept in such an unnatural position, the Animals, in breathing, consume the oxygen air, but
leaves grow sickly, black, or discoloured; as may be
seen in plants trained against a wall. return the nitrogen for the use of the vegetable; while the vegetable retains the nitrogen of the air, and the
Some leaves, if separated from their parent branch, hydrogen of the water, for its own use, and returns
and suspended by a slender thread, will turn their upper the oxygen for ours. How admirable the designs of
surface to the light, and vary their position, as the sun Providence, which make every different part of the
pursues his course. Sword-shaped leaves are an excepcreation thus contribute to the support and renovation
tion; they have no upper or under surface, but are vertof each other.
ical, and do not alter their position. The carbonic air dispersed in the atmosphere, or in Light is considered as a stimulus or agent which dewater, is also necessary to the vegetation of plants, in composes the various nutritive principles, to be found order to provide their carbonic principle, which is a in the air and water. It seems, in many instances, to constituent part of the fibres, oils, mucilage, and other be the sole cause of the expansion of flowers and leaves ;
vegetable principles. It is the basis of all vegetable for when it is withdrawn, they fold together and droop, matter.—[ See Note 2d, on Carbon-post.]
as if dying ; this has been elegantly termed by Linæus, Buds of trees may be truly esteemed individual “the sleep of the plants ;' and the Mimosa pudica, or plants; and, if one of them be planted in the earth, sensitive plant, is a beautiful example of it. This plant, with a cup inverted over it, to prevent its exhalation if kept in a dark room, for a considerable time, will refrom being at first greater than its power of absorption, quire several minutes' exposure to the solar light before it will produce a tree similar to its parent.
the stimulus of the light will dispose it to unfold, or exLinnæus observes, that trees and shrubs are roots pand its leaves. above ground; for, if tree be inverted, leaves will Leaves always turn towards the light; this is necesgrow from the root part, and roots from the trunk sary to the formation of their colour, as may be seen part.
by the common practice of blanching celery, endive, Buds and bulbs are all annual productions, termed, &c. by covering them from the light; and by, plants by Linnæus, the hybernacula, or winter cradles of the raised in darkness, which are of a sickly white. plant. And Darwin observes, that the same term might
Vegetables become destitute of smell as well as of properly be applied to seeds also.
colour, and lose much of their combustibility by growEach bud has a leaf, which is its lungs, appropriated ing in the dark. The celebrated Dr. Robertson, of to it.
Edinburgh, gives an account of a plant found in the Leaves absorb carbonic acid gas, or fixed air, by their drain of a coal-work under ground, which was very upper surface, and give out oxygen gas, or pure respi. luxuriant, with large indented foliage, and perfectly rable air, by their under surface; as first discovered by white. He had not seen any thing like it, nor could Dr. Priestley.
any one inform him what it was. He had the plant Dr. Ingenhousz improved upon this discovery, by with a sod brought into the open air in the light, when observing light to be necessary to these functions; re- in a little time the leaves withered, and soon after new marking that in the dark, leaves give out a bad, or car. leaves began to spring up, of a green colour, and of a bonic air, and that fruits and flowers almost invariably very different shape from that of the old ones. On give out the last mentioned kind of air, at all times, but rolling one of the leaves between his fingers, he found especially in the dark.
that it had the smell of common Tansy, and ultimately Virgil a!'ides to this noxious quality, in his tenth proved to be that plant, which had been so changed eclogue.
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 experi, ments, 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 rende:s 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 duced, as may be discovered by applying it between the the air, light, and heat, by the leaves, becomes a new lips. fuid, which assumes the peculiar flavour and qualities Another secretion to be found in every vegetable, in a of the plant. Gum is one secretion, which oozes from
greater or less degree, is sugar : but generally mixed the cherry, and other trees, resin and turpentine, are of
with gum, sap, or other ingredients. It abounds most in the same nature; as is, also, the milky juice of the fig, fruits, and roots—as the beet, carrot, Sc. but, more parpoppy, &c. Almost all the fruit trees yield some sort ticularly in the Saccharum, or sugar cane. of gum. And a species of the Acacia tree, in Arabia,
The odour of plants, is a volatile oil of a resinous nayields the Gum Arabic, which is the chief nourishment ture communicated to the surrounding atmosphere. This of the nations of those parts, who obtain it in great volatile oil is sometimes distributed through the whole quantities from incisions which they make in the trees. plant, as in the Bohemia Angelica ; sometimes it exists This Gum Arabic is now in frequent use in our own in the bark, as in Cinnamon. Balm and Mint contain country; and forms a good aliment for young children; their oils in the stem and leaves ; Elicampane, and the particularly when on a sea voyage, where milk cannot
Iris of Florence, in the root; Rosemary and Thyme in be commanded.
their leaves, and buds; Lavender, and the Rose, in the Another secretion is Caoutchouc, or Indian rubber,
calyx of their flowers ; Chamomile, Lemon and Orange which is obtained from several species of trees in South Trees, in the petals. Many fruits contain it through America and the East Indies. The botanic names of
their whole substance, such as Peppers, Juniper, &c. the two species found in Cayenne, S. A. are Hævea Oranges and Lemons, in the zest or peeling which encaoutchouc and Jatropha elastica. The Ficus Elastica,
closes them, &c. of South America, is one of the principal trees from Fecula is the general name given to the farinaceous which the Caoutchouc is now procured. The fluid substance contained in all seeds, and in some roots-as collected from the tree by incision; the colour is, at Wheat, Indian corn, the Potato, Parsnip, &c. it is intended first, a yellowish white, but, by exposure to the air, it by Nature for the first aliment of the young plant. becomes dark. Moulds made of clay, in the form of Colour.-The fixed colours of opaque bodies are, in bottles, shoes, &c. are dipped into it repeatedly, and all probability, owing to their absorbing some of the afterwards dried, and, when of a sufficient thickness, the coloured parts of white light, or rays of the sun, and reclay moulds are easily crushed, and the pieces emptied flecting others; their immense variety arising from a mixout.
ture of the reflected primitive colours, in various number The natives make vessels of it for containing water
and proportion. It is impossible to say upon what cause and other liquids; and, while soft, all sorts of designs
the disposition of reflecting certain colours, in preference are traced upon it. On account of its inflammability, it
to others, may depend. The probability is, that it arises is used, at Cayenne, for torches. When warmed, it gives
from the different textures of the surfaces. out a peculiar odour, but not an unpleasant one; from
There are some flowers, the petals of which are in its smoke, a considerable quantity of very fine lamp black
different parts of the same leaf, of different colours ; as may be collected.
of the Heart's Ease, for instance, which, if examined Rectified oil of turpentine, at common temperature,
with a good microscope, will be found to have a different
texture of the blue and yellow parts. The texture, also will afford a complete solution of it; and, when mixed
of the white and red Rose is
different. with a solution of wax, in boiled linseed oil, it composes
It is from reflected rays that we judge of the colour of an elastic varnish, with which they cover balloons ;
objects. The whiteness of paper, &c. is occasioned by and which might be applied to a variety of useful pur
its reflecting the greatest part of all the rays of light that poses.
fall upon it: the blackness of bodies, from their absorbing The fresh cut surface of the Caoutchouc will unite all the seven coloured rays. together by simple contact, and, by a proper pressure, The whiteness of the sun's light arises from the union may be brought so completely in union, as to be no more
of all the primitive colours. These primitive colours are, liable to separate in that part than any other.
red, orange, yellow, green, blue, indigo, and violet ; acThe Caoutchouc, when cut in slips, and softened by cording to Sir Isaac Newton. Dr. Wollaston, who has immersion in boiling water, may be drawn out to seven performed many experiments on the refraction of light, or eight times its original length, and will afterwards, by in a more accurate manner than had been previously its elasticity, resume very nearly its former dimensions. done, confines them to four colours only-red, green, During its extension, a very sensible warmth is pro- blue and violet.
There are seven parts to a flower—the Calyx, Co- The Stamens, according to their number, situation, and rolla, Stamens, Pistils, Pericarpium, Seed, and Recep- proportion, furnish the leading principles of distinction tacle.
in the artificial, or sexual, system of Linnæus. These The Calyx, sometimes called the flower cup, is formed organs are liable to be changed into petals, in what are of one or more green or yellow leaves, situated at a small termed double flowers; and, if the change be complete distance from, or close to the blossom ; its chief use is to the flower will no longer bear a perfect seed. support and protect the other parts of the flower; it is Double flowers become what is botanically termed the envelope in which, in most cases, the tender flower vegetable monsters, by the multiplication of their petals lies, for a time, concealed, as the green leaves of a rose- or nectaries. bud, which cover the blossom, and burst as the flower In those flowers which have many petals, the lowest opens. In the rose, it is situated above the germen, or series of the petals remain unchanged in respect to numseed vessel; but, in the pea, it will be found beneath the ber: hence, the natural number of the petals is easily disseed vessel.
covered, as in poppies, roses, nigella, &c. When remote from the flower, as in the Carrot and The Pistils are the threads situated in the centre of the other umbelliferous plants, [ See Note 3d_post] it is called flower; adhering to the fruit, for the reception of the an Involucre. When contiguous to the flower, or other pollen. A perfect pistil consists of three parts, the gerparts of the fructification, as in the Primrose, &c. it is men, style and stigma. The thickest part, at the bottom called a Perianth.
of the pistil, is called the germen, or seed-bud, and conSome flowers have no Calyx, as the Tulip-others tains the rudiments of the young fruit, or seed; the style have them double, as in the Mallow; but most flowers stands upon the germen, and serves to elevate the stigma have them single, as in the Primrose.
or highest part of the pistil. The style is various in Linnæus considered the Calyx as a prolongation of the length and thickness, but not always present. The stigcortez, or outer bark of the plant.
ma, which is indispensably necessary, is, in some cases, Calyx.—The Perianth is not changed in double flow. seated immediately upon the germen. The shape of the ers; hence the genus, or family may be often discovered stigma is either simple, being little more than a point; or by the calyx.
it is capitate, like a pin's head, as in the Primrose. In The Corolla is formed by the delicate leaves called the most Grasses, the stigmas are amply branched or feathblossom; as the red leaves of a rose, each one of which ery, to detain the pollen. In the Mallow tribe, there is is called a Petal. It is distinguished from the Perianth an abundance of viscid moisture evident in the stigby the fineness of its texture, and, generally, by the gay- ina, and their rich purple or scarlet colour contrasts beauness of its colours. The corolla is considered the termi- tifully with the large yellow pollen, whose bursting, nation of the inner bark, or Liber.
or explosion, may almost be seen with the naked The Stamens are threads within a flower, which have
eye. two parts: the filament, or slender part by which they The Pericarpium, or seed vessel is the germen grown are fastened to the flower; and the anther (which holds to maturity. It varies extremely, being pulpy in apples, the pollen, or fine powder) situated on the top of the fila- fleshy in cherries, juicy in gooseberries, and hard in nuts. ment. They are seated externally with respect to the In other words, the fruit which we eat, is nothing more pistils, internally with respect to the calyx and corolla.
than the pericarps, serving to protect the seeds till They are inserted either into the calyx, the corolla, or
ripe. the receptacle, rarely either upon the germen, or the style, The Seed is that part of every plant by which it is Their number differs in different genera and species of propagated. The part of the seed which contains the flowers, from one to a hundred or more.
the germen vulgarly called the eye, no