lets, as a branch has of forming new branchlets; and the ramifications of its fibrous portion, or skeleton, follow in their development the same general laws as the ramification of boughs. The leaf and the branch are, in fact, homotypal. 2. The simple leaf, consisting of a petiole and single blade, whose margin is entire, is alone to be regarded as the parent leaf, or unit; and it is through repetition of this, that the compound leaf is produced. 3. All leaves with lobes, teeth, crenatures, serratures, or other subdivisions of their margin, however slight, are transitional forms between simple and compound leaves; because such subdivisions of leaf-margin result from an effort at new leaflet-genesis, arrested in its first stages; and are incipient tendencies to self-multiplication on the part of the leaf or leaflet which has its margin so characterized. These facts are too interesting to be omitted. There is nothing random or confused in nature: all that deserves such an epithet is created by the ignorance of man. The leaves, although they may be countless in number, and diversified in appearance as the starry hosts of heaven, nevertheless develop according to laws which are as fixed and immutable as those which guide the planets in their orbits. The more you study them, the more profound will be your conviction of the beauty of their architecture. You will learn to love them, and to love Him more who made them. "Yes! He who guides the rolling orbs above, Spreads every leaf that flutters in the grove; Pours the clear streamlet gliding in the vale; Extends the vast Atlantic's rolling floods, And clothes the forest with its waving woods; The meanest insect on its bosom borne, Live by the fiat of that mighty Hand Who launch'd the spheres, and bade the skies expand.” * Now a few words about the physiology of the leaf. We have shown that the woody system of plants terminates in their leaves in a network of capillary vessels, by means of which the sap is conveyed to all parts of the leaf. The water, charged with nutritive substances from the soil, enters the spongioles of the roots, and, as soon as it enters, becomes subject to the vital action of the plant, undergoes a change of properties, and is called crude or ascending sap. The current ascends through that portion of the wood nearest the bark, enters the leaf by the petiole, passes along the midrib into the veins, veinlets, and capillary vessels of the upper surface of the leaf; its useless water is evaporated; carbonic acid is decomposed, the carbon being retained, and the oxygen evolved. Carbon, or charcoal, constitutes more than one-half of the bulk of plants. Having been rendered nutritious in the leaf, the sap collects again at the extremities of the capillaries, (which * Balfour. communicate with the veinlets, veins, and midrib of the under surface of the leaf,) and re-descends by the bark. The sap is, therefore, thoroughly aërated, and rendered nutritious in the leaf. It is for this reason that leaves have been called "the lungs of plants." The non-nutritious sap entering the leaf corresponds to the venous blood, and the nutritious sap coming out of the leaf to the arterial blood, in animals. Hence the ascending and the descending sap are different. The ascending sap is nearly the same in all plants, containing no noxious qualities, even in the most poisonous. As soon, therefore, as the trees have put on their new leaf-dress, from the moment of its full expansion every leaf is actively engaged in taking in nutritious gases from the atmosphere. The morning and evening dews with which the leaves are covered, the rains which fall upon them from the clouds, are absorbed by them and decomposed as in a laboratory; and it is the same with the sap which they receive from the branches through the leaf-stalk, and which is conveyed to all parts of the leaf by means of the veins, veinlets, and capillaries. Just as the human body, when growing, is formed out of the blood, or nutritious fluid, which circulates through it, so the sap is the formative material out of which plants are constructed. But, in order to be available, it must first circulate through their foliage. The annual additions, in the shape of new shoots, to the extremities and sides of the branches, all proceed from sap which was first rendered nutritious in leaves. It is true, that the roots, by the food which they absorb from the soil, contribute their part to the general structure; but, after all, leaves are the principal architects by which trees are constructed. There is something to one's mind inexpressibly tender and pleasing in the fresh green of the young leaves put forth in spring. How brief, but useful, their lives! The poor dead leaf which we tread upon has expended all its vigour in our service. Where would be our shipping, houses, furniture, if it were not for these timber-architects? But the leaves have other work to do, besides the task of constructing trees. They purify the atmosphere. Every time the sun's bright rays strike their surface, they pour forth streams of oxygen into the atmosphere. All plants do this, from the oak in the woods to the grass in the fields. The poisonous species, as well as the most wholesome, are in this respect public benefactors. Without the purifying influence exercised by the leaves, we could not live. The plant world is the source by which the supply of oxygen is kept up. The prevailing chemical tendencies are to take oxygen from the air. The oxygen of the atmosphere is consumed by burning and decaying bodies, and by the breathing of animals. Immense quantities of carbonic acid are poured into the atmosphere from all these sources, which are as constantly removed by the leaves of plants. The leaves take in the carbonic acid, assimilate the carbon, and give out the oxygen, thus supplying food for the animal creation. The leaves thus keep the air pure. We cannot see the pure oxygen thus given off by the foliage of plants because the air which surrounds them is invisible. Hence for ages it has been poured into the atmosphere unknown to man. But when the same process is carried on in a visible medium such as water, (as in an aquarium,) the escape of the gas from the submerged leaves of the plants is plainly to be seen. It collects on the leaves in the form of air-bells, which rise to the surface. The plants feed upon the carbonic acid which the fish breathe through their gills. Their leaves absorb and decompose it. The carbon is retained, and the oxygen is set at liberty. The water of the aquarium is thus kept pure by the leaves. Thus the same law obtains in the water as in the air; the plants in both instances acting as purifiers. Even in winter, when our woods are without leaves, there is no scarcity of oxygen: for the winds carry off the poisonous carbonic acid, and bring the pure oxygen from the plants of warmer climates, where vegetation is ever active. When I think of the millions of leaves now spread abroad in the atmosphere, all now at work, usefully employed, in purifying the air, in building up trees, in forming edible fruits, or flowers, to cheer us by their beauty and fragrance as we travel along our appointed pathway in life, it seems to me as if I were looking on a world of industry and well-directed energy. I see that instruments apparently insignificant are employed, in the hands of Providence, to bring about the greatest and most important results. I see new beauty in leaves, and can learn a useful moral from their lifehistory. We come now to the last appearance in the natural history of the leaf; namely, the autumn leaf-fall, which marks the close of its allotted period of life, and is generally preceded, at least in most of our trees and shrubs, by a change of colour. Who has not been struck with the beauty of the woods in autumn, when, from one uniform green, the leaves become tinted with every variety of hue, as if nature would rival in autumn, at the close of the year, that beauty and rich variety of colours which she spreads over the landscape in spring, at its commencement? A single night's frost will sometimes completely change the foliage of the forest, and render it a scene worthy of the poet's muse or the painter's pencil. Now, what is the cause of these inimitable and endlessly diversified hues of the leaves at the close of their brief but useful career? The immediate cause lies in the lessened activity of the breathing organs, or pores, of the leaf; resulting from a loss of the illuminating and heating power of the solar rays. The days are shorter, and the nights are longer; the sun is nearer the horizon at mid-day, and his rays strike the earth more obliquely. The natural stimulants to vegetation are thus withdrawn. Oxygen is no more given off by the leaf's pores, and the circulation of sap through its blade ceases. The great natural process of de-oxidation, or the separation of oxygen, not only stops, but is finally reversed. Oxygen is absorbed, and the chlorophyl, or leaf-green, slowly oxidizes itself, and becomes leaf-yellow and leaf-red. The colouring of leaves and fruits undoubtedly arises from the same cause. It is produced by a cessation of the de-oxidating process. It is indicative of a chemical change in the chlorophyl, or contents of the superficial cells,-that substance which gives a green colour to the fruits and leaves. It shows maturity in both, and indicates that nutrition has ceased, that growth has culminated. The leafyellow and leaf-red contribute nothing to the nourishment of the leaf; and, as no more carbonic acid is taken up from the atmosphere, the leaf soon dies, and at last falls from the stem. It is worthy of note, however, that the leaf has fulfilled all its functions in the household of nature up to this point of time, and before it enters upon this last appearance. The leaves fall from the trees when their labours are finished, in forming the wood and bark of the season, in ripening the fruits and seeds; and when they have matured the buds in their axillæ, so that the embryo leaves of the next year are securely sheltered from the storms of winter. No leaf or flower fades or falls before it has fulfilled the purposes of Providence in its creation. PERU THREE CENTURIES AGO. PERU under the Incas was vastly greater, in extent of territory, than the present republic of that name. While this comprises in length less than nineteen degrees of latitude, that stretched over nearly forty degrees, extending from two or three degrees north of the equator to thirty-seven south. In breadth, the limit cannot now be accurately traced. It is only known that it spread from the shores of the Pacific quite beyond the Andes. When invaded by Pizarro, 1524, the Peruvians were found possessed of a degree of comfort, culture, and orderly government, which we at this day contemplate with amazement, and can with difficulty even credit. Indeed, we should look upon the accounts of the earlier historians as largely fanciful, were they not corroborated by remains of their civilization which still exist, and by similar facts among the pagans of China and Japan of the present day. AGRICULTURE. Their coast-border was a rainless, sandy tract, with an average breadth of thirty miles. From this the country rose rapidly into the steep rocky Cordilleras. But, notwithstanding all these disadvantages, this people had invented and carried into practical operation such a system of artificial agriculture as furnished an abundant supply for a large population. Irrigation was secured by canals and subterraneous aqueducts, distributing the mountain streams in all directions. With immense labour earth was transported, and terraces built on the steep mountain-sides, where flourished the fruits of both temperate and tropical climes. The remains of these artificial water-courses still exist in all parts of Peru-palpable records of what would otherwise seem to us incredible progress. These conduits were formed of large slabs of freestone, exactly fitted together, and sometimes extending hundreds of miles, carried through rivers and marshes, and even by tunnel through the solid rock. The sand of the plains was frequently removed, to reach a better soil below. Various manures were employed, and their properties well understood, especially the guano, so much prized and sought by agriculturists of this day. ROADS. The remains of their public roads, intersecting the country in various directions, are still more remarkable testimonials to their superior skill. Two of these extended from Quito to the capital, Cuzco, and thence, southward, in divergent lines, toward Chili. Of these Prescott says: "One of these roads passed over the grand plateau, and the other along the low lands on the borders of the ocean. The former was much the more difficult achievement, from the character of the country. It was conducted over pathless sierras, covered with snow; galleries were cut for leagues through the living rock; rivers were crossed by means of bridges that swung suspended in the air; precipices were scaled by stairways hewn out of the native bed; ravines of hideous depth were filled up with solid masonry; in short, all the difficulties that beset a wild and mountainous region, and which might appal the most courageous engineer of modern times, were encountered and successfully overcome. The length of the road, of which scattered fragments only remain, is variously estimated at from fifteen hundred to two thousand miles; and stone pillars, in the manner of European milestones, were erected at stated intervals of somewhat more than a league all along the route. Its breadth scarcely exceeded twenty feet. It was built of heavy flags of freestone, and, in some parts, at least, covered with a bituminous cement, which time has made harder than the stone itself. In some places, where the ravines have been filled up with masonry, the mountain torrents, wearing on it for ages, have gradually eaten a way through the base, and left the superincumbent mass-such is the cohesion of materials-still spanning the valley like an arch." Humboldt says: "The great road of the Incas was one of the greatest and most useful works ever executed by man." The fibres of the maguey, the tough osier of the country, twisted into cables as thick as a man's body, furnish the material of their bridges. Several of these great cables, bound together and strongly fastened at the ends, formed the bridge, which was covered with wood, and guarded on each edge by a railing. Some of these bridges spanned chasms. two hundred feet broad, covering a frightful abyss, where dark waters foamed and tumbled many fathoms below. The streams on the coast-road, being broad and tranquil, were crossed on rafts, using sails, the only instance of their use known among the American Indians. All along these highways, at distances of ten or twelve miles, were erected caravansaries, to accommodate travellers, especially the Inca and his suite. Some were supplied with barracks and fortifications, evidently intended to accommodate the royal armies in passing across the country. Posts for runners, to carry dispatches, were also built all along these roads; and messages were thus transmitted at the rate of one hundred |