CHAPTER THIRD.

WEALTH AND NATURE.

inquiry into the nature and The word wealth is used in

§ 36. WE are engaged in "an causes of the wealth of nations." two senses; as meaning either the aggregate of possessions that minister to man's necessities and tastes, or the possession of an abundance of such objects. In the former or popular sense wealth is the measure of man's power over nature; in the latter or scientific sense it is the power itself developed to more than the average degree.

Closely connected with the term wealth is the term value. The one is the antithesis of the other. If wealth is the measure of man's power over nature, value is the measure of nature's power over man,―of the resistance that she offers to his efforts to master her. Some of the natural substances are to be had everywhere, always and in the form needed for man's consumption. These have no value, though the very highest utility. Others, such as the water for the supply of a great city, need to be changed in place, and have a value proportional to the cost of their transfer. Others need to be changed in form by manufacture as well as changed in place before their use, and have a still higher value. In other instances the resistance takes the form of scarcity, and is therefore in some degree insuperable, and the degree of the value is still higher.

§ 37. Man stands in close relation to nature, as the possessor of a body which forms part of the physical world. He therefore needs the services of nature continually. His body is undergoing incessant decays and renewals. Motion, respiration, sensation, digestion, circulation of the blood, even thought itself wear away its tissues, and unless this waste be replaced the man must die literally of exhaustion.

Furthermore, these vital processes can be carried on only in the presence of a certain amount of animal heat, which must be

supplied from within, and (in most climates) shielded from without to prevent its excessive radiation.

The chemical substances that form the bodily frame are chiefly Oxygen, Hydrogen, Carbon and Nitrogen. The two first in the form of water make 75 per cent. of the whole body, and 83 per cent. of the most ccmmon foods. Berzelius says that the living organism is to be regarded as a mass diffused in water, and another chemist has humorously defined man as fifty pounds of nitrogen and carbon suspended in six buckets-full of

water.

The starch which forms so large an element in the ordinary foods enters into the composition of none of the tissues. It is consumed in the lungs to furnish the vital heat, and breathed off as carbonic acid. § 38. Hence man's two great material necessities are food and clothing. The desires for these furnish the motive to the vastest activities of the race. As his brain expands, indeed, and as society develops, other desires grow into life and become motives to action; but these two are universal. Others are voluntary; these are enforced by the sensations of hunger and cold. Others are directed to comforts or luxuries; these to things necessary and indispensable.

The productions of the three kingdoms of nature do not equally satisfy these desires. Though there are apparent exceptions, it niay be laid down as a rule that he obtains food and clothing from the animal and vegetable kingdoms only. The animal kingdom as a whole is supported by the vegetable, which in its turn depends upon the abundance and fitness of the great mixtures of vegetable and mineral substances which we call soil. Only the lowest type of vegetation can support its life upon mineral food alone.

§ 39. We can trace the story of the earth's development back to a period when vegetation, and therefore soil, did not yet exist upon its surface. Some of the natural agents already at work were indeed preparing for the formation of soil. Glacial corrosion and other violent forms of action were grinding masses of rock into fine sand, and the frosts were chipping away the edges and faces of the rocks by sudden expansion of the water that they had absorbed.

Vegetation began with the lichens and the mosses, which

THE HISTORY OF THE SOIL.

43

secured a foothold on the surface of the rocks, and slowly crumbled down a few grains of sand from the hard mass (by the action of the oxalic acid which they secrete), and dying, mingled therewith the ashes of their own decay. This furnished the first soil for the next highest order of vegetable life, and thus through successive orders of vegetable life the soil was deepened and enriched.

As illustrating Goethe's law of progress by differentiation of the parts from the whole and from each other (see 230), it is worth while to notice the stages of this development as given in the great classification of Oken. First come the acotyledons (lichens, mosses, &c.), which have neither root nor stem, neither bark nor wood, neither leaves nor seeds. Then the monocotyledons (grasses, lilies and palms), which have no branches nor true leaves, but may have either woody stems, or venous liber, or bark-never the three united. The third are the dicotyledons (fruit and forest trees, &c.), which unite all these parts in one organism. This process of the formation of soil on a rocky surface by successive vegetable growths, still takes place with some modifications in the coral islands of the Pacific. When the coral polyp has raised its rocky fortress above the sea level, the surface is soon strewed with fragments that the waves break off and grind into sand, which is mixed with the remains of the coral polyp. A cocoanut carried safely in its rough husk on a long voyage is washed ashore and takes root. The decay of its leaves forms a new soil, and the birds that rest on its branches bring the seeds of other vegetation in their crops, so that a multifarious growth rapidly covers the barren rock.

§ 40. The sustenance which the growing plant derives from the mineral kingdom is not taken solely nor even mainly from the soil through its roots, but from the air through its leaves. Were it otherwise, the growth of the soil must stop as soon as its depth became as great as that to which the plants thrust down their roots. But six feet of soil is not uncommonly found on the prairies of the West, and even that depth still increasing. The chief food of plants is carbonic acid, one of the elements of the air, which in the early geological ages was so abundant that only vegetable life could have existed on the earth's surface. The

first luxuriant vegetable growths, the mosses and the ferns absorbed it in vast quantities, growing with marvellous rapidity, and forming the deposits of decayed vegetation, now known to us as coal, after having been subjected to vast pressure for unnumbered ages. By burning this as fuel we give back to the atmosphere a small part of the carbonic acid that once saturated it, and thus furnish food for new vegetation from the substance of those which flourished ages ago. Nothing that is consumed or that decays upon the earth's surface is wasted;—nothing is wasted but what goes into the sea. 'Atmospheric air is the grand receptacle from which all things spring and to which they will return. It is the cradle of vegetable and the coffin of animal life" (Dr. Jno. W. Draper).

Carbonic acid forms but a thousandth part of the chemical mixture that we call air.

.

§ 41. The foliage of the plant is a vegetable substitute for mouth and lungs. It presents a vast absorptive surface to the air through which it drinks in carbonic acid and transmutes it into woody fibre. To pluck all the leaves of a tree in the early summer would be to kill it by suffocation and starvation. From the vast storehouse of the air the plant draws its food, and the atmospheric supply is kept up by the decay of other plants, by the respiration of animals, and by the consumption of wood and coal as fuel. When the plant dies, a small percentage escapes back to the air again, but the great mass is added to the wealth of the soil, from which so little was taken.

The proportion of sustenance that a plant takes from the air has been ascertained by experiment to be about nine parts in ten. In one case a willow tree weighing five pounds was planted in a box, in two hundred pounds of soil that had been carefully dried and weighed. To prevent the settlement of dust in any appreciable quantity, the soil was covered with a metal plate. pierced with very fine holes to allow the free passage of the air; and it was moistened with rain-water only. After a few years the tree was removed, and the soil was carefully collected and

FERTILITY A PROCESS. THE SOIL A MIXTURE. 45

ried. On weighing them it was found that the tree had gained sixty-seven pounds and the soil had lost eight ounces.

The late Prof. J. F. Frazer told me that while engaged in the geological survey of Pennsylvania he found a willow tree growing in the cleft of a rock where there was absolutely no soil whatever, but a continual ooze of water was keeping the cleft moist.

§ 42. The fertility of the earth is therefore not an accomplished fact, but a vast process that is still going on. Nature is preparing for the time when man will make still larger demands upon her resources than at present. Even when the fertility of a piece of ground has been exhausted by continual abuse, she brings her restorative energies into play. Thus the abandoned tobacco plantations of Eastern Virginia have been covered by a growth of pines, whose long taproots reach down below the exhausted surface, and bring up mineral substances, which after the fall of the leaves and the decay of the stems enrich the soil. A similar instrument of recuperation nature furnishes to the farmer in the clover plant, whose peculiarity it is to thrust down its roots to the mineral subsoil and feed only upon that.

§ 43. The soil, it has been already said, is a mixture of mineral and vegetable matter. The former, even when less in amount, is by no means inferior in importance. It predominates in the subsoil, and in the best soils appears mainly as silicious sand and clay. The first use of the former is to keep the soil porous and make it ready to receive, of the latter to keep it compact and able to retain. An excess of either substance imparts to the soil a corresponding defect.

In the plant the silex or flint of the sand reappears as the skeleton. The slight and fragile stalks of our grains and grasses are kept upright under their load of seed by a thin coating or varnish of silica. Every acre of wheat requires from 93 to 150 pounds. This mineral element is but slightly present in the fruits and seeds which man carries from the soil; somewhat more largely in the stems and trunks of trees, but most of all in the leaves which return to the soil at once, or after having served as food for cattle. The leaves of trees contain fifteen times as much as the trunks.