QUANTITY, DISTRIBUTION, AND OFFICES OF THE VEGETABLE.
In contemplating nature there are few things which give more delight than the beauty and variety of the vegetation which clothes the surface of the earth, whether it be that we contemplate the grassy covering of the plains of the Old World, or the immense "prairies" of the New, spreading out as it were into seas of grass, and giving food and shelter to thousands of wild animals; or gaze upon the rocky height of some vast mountain range, and see the gigantic oak or pine, forming by their wide-spread shades the solemn forest which extends for miles beneath us, and which forms a shelter for the various tribes of birds, monkeys, and other animals, to whom it is a home of happiness and plenty—under every aspect the contemplation of nature's clothing fills the mind with awe and admiration.
There is hardly anything more refreshing to the mind than the contemplation of trees and shrubs congregated into a wood, the floor of which is carpeted with mosses and flowers, where the gigantic and gnarled trunks of the forest trees covered with many-coloured lichens starting up all round, circumscribe the view, while the wide-spreading boughs and the leafy canopy overhead exclude the sun's rays. It is here that one views nature in her purest forms and colours, untouched by the destroying hand of artificial arrangement.
The immense preponderance of the vegetable over the animal world in quantity compensates somewhat for the superior organisation and the intelligence of the latter, which must be studied in the individual, while the vegetable world, which can be contemplated in the mass, almost overwhelms the imagination with its vastness. It is indeed impossible to compute the amount of vegetation in the great forests of America and Russia (in which latter country are the largest in the world), covering hundreds, nay thousands, of square miles with one continuous growth of timber. That forest in Russia through which the river Pechora flows, extends over a space of 150,000 square miles! The whole mass of animated existence sinks into insignificance when compared in quantity with this; and when to these forest-tracts are added the thousands of square miles of grass and heaths which grow in some climates with wonderful luxuriance, the amount of the vegetable kingdom is at once placed beyond all comparison with the animal kingdom in point of quantity. Cooper, in his American novels, describes the prairies as great seas of grass extending as far as the eye can reach, and rising to a height of 8 or 10 feet; and Humboldt describes some of the grasses on the plains of the Oronoco, as being so gigantic that they measure 18 feet from knot to knot, and says the Indians use them for blow-pipes to shoot their poisoned arrows from. And—as though it were not sufficient that the earth should bring forth everywhere all kinds of trees, shrubs, and grasses—the waters of the ocean itself are often filled with vegetable life; in some tracks the tangled sea-weed (Fucus Natans) is so dense as to impede the onward progress of ships for hundreds of miles together.
Humboldt, in his "Views of Nature," describing the two great banks of sea-weed, says: "The two banks of sea-weed, together with the transverse band uniting them, constitute the Sargasso Sea of the older writers, and collectively occupy an area equal to six or seven times that of Germany."
FIG. 1.—DIATOMA VULGARIS.
FIG. 2.—VARIOUS DIATOMACEÆ.
Nor is this the only vegetation which the great world of waters contains, for if we descend from the contemplation of its larger members we find them even surpassed in quantity by others of such extreme smallness, that they can only be seen individually by means of the microscope, but which exist in such prodigious quantities that the mind can hardly realise the fact. These vegetable atoms have been so increasing and depositing their minute coverings at the bottom of most parts of the ocean, that for hundreds of miles their beds are composed of nothing else, and it has been found that most of the great changes on the surface of the earth have been effected by these minute creatures and their companions of the animal world; for as we find chalk-downs and coral-reefs formed by the remains of microscopic animals, so productions of equal extent have been formed by the smallest members of the vegetable kingdom, chiefly the "Diatomaceæ," a race of minute vegetable productions which propagate by sub-division and have the power of withdrawing earthy matters from the waters in which they live, which forms a sort of shell or covering; this shell at their death remains indestructible and gradually accumulates in the bed of the sea (fig. 1). Examination of the various strata of the earth shows that chains of hills, beds of marl, and almost every kind of soil, whether superficial or raised from a depth, consist in a great proportion of the earthy remains of these minute plants. These tracts of land were once the beds of oceans which were thus gradually filled up. The waters of the Antarctic Ocean are often opaque and quite brown from the multiplicity of these creatures, the lead used on shipboard for sounding coming up from the bottom covered with what appears to be mud, but which on a microscopic examination proves to be nothing else than the shells of these and allied species (fig. 2). Thus we find the land and the waters are everywhere full of vegetable life; the air itself moreover is so filled with the germs of vegetable and animal creations, that it is quite impossible to exclude a portion so small that it shall not contain any; in proof of which, any organic substance set by for a few days in a vessel ever so carefully closed, is shortly covered with a growth of mould consisting of fungi, which under the microscope present most beautiful forms and colours (fig. 3). The cause of this is a deposit from the air of the spores or germs of these creatures, and the nature of the decomposing substance into which they fall often determines the race or tribe which shall come to life and inhabit it, showing plainly that but a few of these only among many come to maturity, just as when a variety of seeds are thrown on any particular kind of soil, only those to which the soil may be suitable come to perfection.
FIG. 3.—a a, MOULD FROM AN OLD BONE—b, MOULD FROM JAM.
Dr. Carpenter in his work on the microscope says:—"There are scarcely any microscopic objects more beautiful than some of those forms of mould or mildew which are so commonly found growing upon the surface of jams and preserves, especially when they are viewed with a low magnifying power and by reflected light; for they present themselves as a forest of stems and branches of extremely varied and elegant forms, loaded with fruit of singular delicacy of conformation, all glistening brightly on a dark ground.
"The universality of the appearance of these simple forms of fungi upon all spots favourable to their development, has given rise to the belief that they are spontaneously produced by decaying substances, but there is no occasion for this mode of accounting for it, since the extraordinary means adopted by nature for the production and diffusion of the germs of these plants adequately suffices to explain the facts of the case.
"The number of sporules which any one fungus may develope is almost incalculable; a single individual of the "puff-ball" tribe, has been computed to send forth no fewer than ten millions. And their minuteness is such that they are scattered through the air in the finest possible dust, so that it is difficult to conceive of a place from which they should be excluded."
Pure water exposed to the air does not afford nourishment to the germs which fall into it till a sufficient number of them shall have been deposited to form a food for those which come after them; but if we mix with the water any soluble vegetable or animal matter, in a short time the microscope will detect the growth of the germs that are being deposited, for where nourishment is, there only can they be developed. These germs are capable of existing for an indefinite period, either floating in the water, or blown about by the air, and have been detected hundreds of miles from land, the rigging and sails of ships far away from shore are often covered with what sailors suppose to be sand blown from the land, but which are organic substances, either vegetable or animal. According to Humboldt, the Red Sea has derived its name from the fact that at certain seasons the surface of the water has a reddish appearance, and this (as he says) he was fortunate enough to observe, which colour he found to be due to myriads of red fungi which had formed on the surface. The seeds of some plants are furnished with minute wings or plumes which cause them to be borne on the air or floated on the water (fig. 4), to fertilise some barren spot, perhaps a coral reef which has at length reached the surface of the water and which ascends no higher, for the little creatures which built it are aquatic and cannot live exposed to the air; this coral reef now becomes a receptacle for sea-weed and fungi, which float on the surface of the ocean, are washed on to the reef, die, decay, and leave behind a thin layer of mould, which process being repeated again and again, forms an elevated edge to the reef, enclosing a lake or "lagoon" as it is called, the waters of which evaporate and the space is filled up in the same way as the edge was formed, together with the excrements of birds, &c., forming layer after layer of mould, and the surface becomes fit for the growth of larger seeds, as the cocoa-nut, banana, &c., which are drifted on to it by the waves; in this way a coral reef becomes an island fit to be inhabited by man and other animals.
FIG. 4.—SEEDS WITH PAPPI.
The vegetable kingdom forms a mysterious link between the mineral and animal kingdoms, and binds all creation into one grand and unspeakably beautiful whole. There are certain substances from which the vegetable derives its nourishment, namely water, carbonic acid, and ammonia, which, though strictly inorganic, are yet not simple or elementary substances, but consist of pairs of elements combined. Thus water consists of oxygen and hydrogen, carbonic acid of oxygen and carbon, and ammonia of hydrogen and nitrogen. All these aliments of the vegetable kingdom exist in the air, and in sufficient quantities to supply all the requirements of vegetation; so that the air, together with a few metallic oxides (salts) derived from the earth, furnishes food for the whole vegetable tribe, from the highest to the lowest, and these vegetables in their turn supply all the food which the animal tribes consume, for although one animal feeds upon others, yet these must previously have derived their nourishment from vegetable matter. Vegetables not only supply food properly so called, but likewise that which is essential to respiration, for besides separating all noxious excess of carbonic acid from the air, they are an inexhaustible source of oxygen, the element essential to respiration, and consequently animal life. This supply of oxygen by vegetables compensates for that which is consumed in respiration by animals, and thereby maintains the atmosphere in a state proper to be breathed. That plants do thus absorb carbonic acid and give out oxygen, can be proved in the most certain manner, if the green parts of a plant be placed in water holding carbonic acid in solution, and exposed to sunshine; the carbonic acid will shortly be found to have disappeared from the water, while oxygen gas is evolved and can be collected, its quantity being exactly equal to the carbonic acid which the water contained.
Besides furnishing food and oxygen for the nourishment of animals, vegetables afford a shelter from the burning rays of the sun in hot climates, not only to man, but to those hundreds of wild animals whose proper home is in the forest. Humboldt says he found in South America forests composed of such close growth, that it was quite impossible even for the wild animals to penetrate into them, except at a few places, and that the jaguar often lives for weeks in the trees without descending to the ground, preying upon the monkey tribes and other animals, which are found in almost incredible numbers there; and Dr. Livingstone thus describes the forests of Africa:—"The forests became more dense as we went north. We travelled much more in the deep gloom of the forest than in open sunlight. No passage existed on either side of the narrow path made by the axe. Large climbing plants entwined themselves round the trunks and branches of gigantic trees, like boa-constrictors, and they often do constrict the trees by which they rise, and, killing them, stand erect themselves."
These woods, as well as the grass and herbage of the plains, afford an enormously extended evaporating surface, and act, in the heart of hot countries, as inland seas, giving out clouds of vapour, which ascend and are condensed in the form of rain; in this way the surface of the earth is cooled, the fluid (far away from its proper source, the ocean) is economised and fertilises a greater space of surface. Vegetation also acts in preserving the surface of the earth from those ravages which both wind and rain would otherwise effect; the great deserts have been levelled by these causes, the earth not being of a quality to support vegetation. Cattlin says, that in North America he frequently met with great conical-shaped mounds of earth devoid of vegetation, and which were fast being levelled by the rains, at every fall of which gullies were formed on their sides, down which the mud poured in streams; now, had these been of a quality to support a covering of grass, their size and form would have remained unchanged for centuries. Railway embankments are often sown with grass seeds, to prevent injury to them, especially where this covering is not likely to come soon, as in the vicinity of large towns.
Thus it is seen that the vegetable kingdom far exceeds the animal in quantity, that it is everywhere distributed, that it affords nourishment and shelter to animals, preserves the air fit for respiration, keeps down the excess of heat, and preserves the form of the surface of the earth.