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Transactions of the Highland and Agricultural Society of Scotland
Manual of Agriculture


MANUAL OF AGRICULTURE, INCLUDING THE APPLICATION THERETO OF CHEMISTRY, GEOLOGY, BOTANY, ANIMAL PHYSIOLOGY, AND METEOROLOGY.

By Richard Henderson, Coldstream, Berwickshire.
[Premium—Twenty-Five Sovereigns.]

Chapter I.—Introduction.

Agriculture, literally, tillage of the ground, is both a science and an art: a science, in so far as its principles are co-extensive with those of chemistry and the cognate physical sciences; an art, in the intelligent direction of these principles to the practical end of best developing the food-producing properties of the soil. The importance of founding the practice of this art in this country upon a more thorough and widely diffused knowledge of its scientific principles will be granted, when it is stated on the best authority, that by a generally thorough cultivation of the soil the annual agricultural products of Great Britain might be doubled in quantity. And it is a fact, that we annually import food from other countries to the value of L.80,000,000 sterling, which fact may, undoubtedly, increase commerce and beget the comity of nations; but at the same time it might leave us in a hazardous position in the event of a sudden political emergency. Agriculture is the oldest of the arts; for we may rest assured that Adam delved, however problematical may be the question whether "Eve span." Amongst the ancient Egyptians, and later, under the Roman Empire, its practice attained a high measure of success, but it rested on a merely empirical basis. Not before the present century has any general scientific knowledge of the laws of nature, which regulate the art, characterised its numerous professors.

Whatever may be the varieties of soil and climate—and these, together with the subsidiary circumstances of available human labour and of markets, may be said to determine the particular mode of agriculture suitable for any locality,—the great fundamental laws, in conformity with which alone is truly successful practice possible, are comprised in the physical sciences following:—viz., Chemistry, Botany, Geology, Animal Physiology, and Meteorology. The last, to reverse the order, under the simple name of "weather," is a subject of interest, scientific or otherwise, to every farmer. It teaches a system of forecast of weather changes. Forewarning is forearming; and by adjusting farm operations accordingly, great loss is avoided. Animal Physiology treats of the bodily structure and the functions of the bodily organs of our domesticated animals; and in that department of it we earn the general treatment best fitted to ensure their healthy procreation and profitable development. Geology has to do with the formation and nature of the Earth's crust, the forces which have been at work in preparing it for its present condition, and those at present affecting its modification. In its relation to agriculture, it reveals to the farmer the various compositions of soils, and their derivation, and it gives him practical hints upon drainage operations. Botany, in its bearing upon agriculture, teaches the systematic classification of the various plants scattered over the face of the globe, their native localities, the variety of soil and climate best suited to the cultivation and growth of individual plants, and their internal structure, and modes of reproduction and growth. Chemistry—the grammar, so to speak, of all the physical sciences—acquaints us with the primary original materials of earth, air, and water, and consequently of all animal and vegetable life. As being the most fundamental of all the physical sciences bearing upon agriculture, its consideration in that relation comes naturally first.

Chapter II.—Of Chemistry.

Our earth, with its sea and atmosphere, and all whatsover therein contained, is composed of about sixty-three original and simple elements, whose substance cannot be further reduced. Of these only four occur in the atmosphere; upwards of thirty have been found in sea water; whilst in the solid structure of the globe, the whole are to be found in varying proportions. They can exist in three states, viz., solid, liquid, or gaseous; [Liquids are technically known as incompressible fluids, and gasses as compressible fluids.] and that either alone or in combination. And such changes of state take place at fixed degrees of heat or temperature for each. The several elements consist of an aggregation of atoms, those of each particular elements being always alike in material weight and volume. In the gaseous state, and whilst free from combination, the atoms of all the elements are of equal volume; but they vary in weight, and also, of course, in point of material. Although not in an apparent manner, the elements can, under certain conditions, be artificially reduced to their atomic state—i.e., isolation of individual atoms—by the aid of heat or electricity. When thus reduced to the free, or as it is called, the nascent state, the atoms of any element have a tendency to unite with those of one or more different elements, when brought into contact with the latter. This is being continually effected through the agency of natural means; and, as will be seen, it is the cause of all physical change on our planet. The atoms of one element unite with those of another in certain fixed invariable proportions, and they have a greater tendency to unite with, or affinity for, those of some elements than of others. What is known as chemical combination is this union of the atoms of different elements, and the result is a compound body or substance. The least number of atoms in such an union, or rather, the least quantity of such a compound body, that can be formed, or exist in a free state, is called a molecule; wherefore, chemical compounds are composed of an aggregation of molecules. Still more complicated chemical compounds are formed by the union of the molecules of different compound bodies. The proportion of molecules requisite with a given quantity of different molecules, to form a new compound, is called the equivalent of the latter. In all chemical action, heat is given off or taken up; in the process of combination, it is evolved, in that of separation, its absorption is requisite thereto. A certain amount of heat is absorbed by all substances while they pass from the solid to the liquid, and from the liquid to the gaseous forms, which heat remains in abeyance — latent, until such substances are again transformed into their original forms, and then it is evolved. When the majority of chemical bodies assume the solid, instead of the liquid or gaseous form, they appear as small particles of a definite geometrical shape, called crystals, each compound invariably preserving its own peculiarly distinctive crystaline form. Moreover, whatever be the size of any united accumulation of specific crystals, the aggregate mass shapes itself into the geometrical type of its minutest constituent crystal. Chemical bodies not observing this law, in the process of their solidification, assume a structureless texture, and are called amorphous, literally, without form. Again, numerous compounds arising through the agency of animal and plant life, show neither a crystaline nor an amorphous, but a cellular or organised texture. A chemical combination of elements is something quite distinct from mixture pure and simple —that is to say, mere mechanical union. In the latter case, there is no interchange of the several atoms,—no chemical action takes place. There is merely mechanical juxtaposition of particles. By way of illustration, take the preparation of common mortar. There, before the addition of water to the lime shells, the latter are in the state called caustic lime, or oxide of calcium—a combination of the simple metallic element calcium, and the simple gaseous element oxygen—one atom of the one in chemical combination with one atom of the other; whence its technical symbol in chemistry Ca. O. Upon the addition of water, a violent disturbance in the mass occurs, together with the evolution of much heat. And this action continues until the certain amount of water requisite to enter into combination with all the caustic lime present has been added. Any amount of water superadded thereto, and the sand, are simply mixed with it mechanically. No further immediate chemical action ensues.

Another illustration of chemical combination is the common class-room experiment, showing the composition of water, wherein the two gases oxygen and hydrogen are mixed in the proper proportions in a vessel. Still there is but mechanical union till a flame is applied, when the two gases instantaneously explode with violence, and the chemical combination will be found to have produced an entirely new body, a liquid-water.

The elements are, according to their possession of certain physical properties, arbitrarily divided into two classes—the metals and the non-metals. And those, again, which are met with in the combination present in animal and vegetable life, are further classified into two groups, viz., organic and inorganic.

The organic, in all substances, are capable of being separated from the inorganic, and driven off in the shape of gases, by simple combustion. The inorganic always remain, as the ashes of the substance consumed. In the organic elements life, animal or vegetable, may be said to have had its seat.

The terms, however, have another application,—"organic" being used in the case of those complicated compounds whereof the element carbon is an invariable constituent; "inorganic," in that of the simpler compounds, with fewer atoms composing their molecules. Chemical compounds, according to their marked characteristics, are all classified under three divisions, viz., acids, bases, and salts. The first two exhibit quite different properties; but when, under certain conditions, they are brought into contact, they lose their distinguishing properties and unite to form the neutral compounds of the third division.

Particular acids are stronger than others, and can, so to speak, expel the weaker—those acids which have a less degree of affinity for the base—from the salts, and occupy the place in their stead. From a limited point of view, the most characteristic acids may be said to possess a sour taste, and the property of turning a solution of blue litmus to a red colour; whilst, on the other hand, the most marked bases, such as potash, soda, ammonia, and lime—alkalies so called—can restore the solution of blue litmus thus reddened to its original colour, and they have a peculiar soapy taste. To the chemist, however, the terms "acids" and "base" imply the possession of properties of a much wider and less limited description.

Out of all the chemical elements, about 18 only are discover- . able in the blood and tissues of man and the lower animals, and in the juices and fibres of plants. Hence, these should exist in greater or less quantity in our cultivated soils, seeing that animal life depends primarily upon vegetable life, and that the latter again derives its main sustenance directly from the soil.

Of these 18, none exist in the free state, but as various compounds, in bodies animal and vegetable. They are:—

1st. Organic, comprising Oxygen, Hydrogen, Nitrogen, and Carbon; and
2d. Inorganic, comprising Silicon, Aluminium, Potassium, Sodium, Calcium, Magnesium, Phosphorus, Sulphur, Iron, Manganese, Chlorine, Bromine, Iodine, and Fluorine.

Oxygen.—Of all the elements, oxygen occurs the most abundantly throughout nature. It exists free in the atmosphere, of its total bulk contributing 1-5th part. In combination with other elements, it constitutes one-half the weight of the solid globe, and 8-9ths of that of water. It is an invisible gas, tasteless, and without smell. Excepting fluorine, it enters into combination with all the elements. In this process, called oxidation, heat is always, light sometimes, evolved. Flame consists of gas in a high state of ignition, caused by the oxidation of the substance consumed. During combustion, new chemical compounds, chiefly gaseous, are being formed, but no element is annihilated.; Animals inhale oxygen into their lungs, where it oxidises certain elements in the blood and tissues, and thus keeps up the degree of warmth necessary for life. Oxidation is much more rapid in undiluted oxygen than in the atmosphere.

Hydrogen is another invisible gas, devoid of taste and smell. Its principal combination is with oxygen, in the form of water—two atoms of hydrogen to one of oxygen,—whence its chemical symbol H2O. Hydrogen is the lightest of all the elements, and it is taken as the unit with which to compare the others, The symbolical letters, it may be remarked, representing the different elements, represent also their combining weights, or the weight of their respective atoms compared with hydrogen's. An atom, or any volume of oxygen, is 16 times the weight of an atom or equal volume of hydrogen; and as water is composed of two parts of hydrogen to one of oxygen, the latter constitutes 8-9ths of the weight and a third part of the volume of water. Hydrogen has been found free in sundry volcanic gases, and it can be obtained from the decomposition of water, through the agency of certain metals. Water enters into combination with many substances, and in so doing, in almost every instance, one of the atoms of hydrogen, in the molecule of water, is replaced by some equivalent in the compound into which it enters, and free hydrogen is given off.

Nitrogen is also an invisible, inodorous, tasteless gas. It exists free in the atmosphere, mixed with oxygen, forming about 4-5ths of the bulk of atmospheric air. It is a most inert element, incapable of entering into direct combination with any other except oxygen, and even then with difficulty, and only by means of the electric spark. By very indirect processes, however, it enters into important combinations with hydrogen as well as with oxygen. It forms five several oxides, the principal one of which is a combination of 5 atoms of oxygen with 2 of nitrogen —N2O5, which, combined with a molecule of water, constitutes nitric acid, H2O + N2O5 = 2 (HNO3). With hydrogen, it forms ammonia—1 atom of nitrogen to 3 of hydrogen—NH3.

Carbon we meet with free and as a solid in three distinct forms, physically different, but possessing in common the same chemical properties. These are:—(a.) The precious diamond; (b.) graphite or plumbago, popularly known as black lead; and (c.) charcoal. It is found neither as a fluid nor a gas in the free state. It is present in all organised structures. It forms about 50 per cent. of the residue of plant life when the latter is charred, and access of atmospheric air or oxygen prevented, for oxidised carbon escapes as a gas. It enters into exceedingly complicated compounds, the consideration of which forms a special branch of chemical science, called organic chemistry. Combined with oxygen, it forms carbonic acid CO2—an invisible, ponderous gas.

Plant life is unable to assimilate these organic elements in their free state, but only when they exist in combination with certain other elements. Such compounds are water, nitric acid, ammonia, and carbonic acid. In the organised structures of plants these compounds are broken up or resolved, and their constituent parts economised in the building up of new organisations, which in their turn are metamorphosed for the structure of animal life. The atmosphere and soil, but chiefly the latter, are the media through which these elements are rendered available for the necessities of plant life.

Silicon.—Next directing the attention to the inorganic elements, it is to be remarked that silicon, next to oxygen, is the most abundant element in nature. It does not occur free, but as an oxide, SiO2, known as silicic or silica acid. In that state it is nearly pure, under the forms of quartz, flint, and sand. Silica, though in a variable quantity, is always present in the ashes of plants. Chiefly is it plentiful in cereals and grasses. It forms the hard glistening surface of straw and bamboo. In most plants, however, it rarely exceeds 5 or 6 per cent. of the residual ash.

Aluminium is a bright lustrous metal of excessive lightness. It does not occur free, but as an oxide—A12O3. There is but a slight trace of it in the ashes of plants, although in combination with silica, under the name of silicate of alumina, it forms the basis of the clay of our soil. From an agricultural point of view, it is therefore of importance.

Potassium, when with difficulty prepared free, is a light metal of silvery appearance, and so soft as easily to be cut with a knife. Thrown into water, it decomposes it. One atom of potassium replaces one atom of hydrogen, and heat is evolved in sufficient quantity to ignite the liberated hydrogen. It rapidly absorbs oxygen from the atmosphere, forming the oxide K2O—Kalium being the technical name given to potassium in chemistry. This oxide has a powerful affinity for water. The combination is potash KHO. The change can be represented by a chemical equation as follows:—K2O + H2O=2(KHO). One molecule of oxide of potassium and one of water form two molcules of potash. It is one of the most important compounds in the ash of plants, forming from 20 to 50 per cent. of its weight. It is mainly present in roots and tubers, seeds and grasses, and in the leaves and branches of trees.

Sodium.—Sodium is a metal closely resembling potassium in all its features. These two, together with four other less important elements, which do not enter into living structures, are called the metals of the alkalies. They decompose water at all temperatures, and combining violently with oxygen, they form powerful caustic and alkaline basic oxides, which possess a strong affinity for water, which last cannot be expelled from them by heat agency alone. The principal oxide of sodium is Na2O— Natrium = sodium. This combined with water is HNaO, or soda. The compounds of sodium are widely distributed, and along with those of potassium abound in the primary rocks, as well as in sea-water. Soda is a less important constituent, and forms a less proportion of the ash of plants than potash. It is more largely present in the ash of marine than of land plants.

Calcium.—-Calcium, when free, is a light yellow metal. Readily combining with the oxygen of the atmosphere, it becomes the oxide CaO,—lime. Lime has a strong affinity for water, and decomposes it at any temperature. It forms with water CaOH2O, or slaked lime. Calcium compounds largely from the rock-forming materials of the globe, in such varieties as, e.g., chalk and limestone. From the last, lime for ordinary use is prepared, by driving off, by means of heat, the carbonic acid,— limestone being a salt called carbonate of lime, composed of carbonic acid and lime as a base. Lime discharges most important functions in the soil, in the way of breaking up compounds, liberating their constituents in such a manner, as to render them readily available for the purposes of plant life. Its percentage in plant ash, varies as much as from 1 to 40.

Magnesium is a silvery white metal. If strongly heated, it takes fire in- the air, burning with a dazzling white light, and forming the oxide MgO, known as magnesia. In dry air it does not oxidise. It is slowly acted upon by cold water, more rapidly by hot. As the carbonate of magnesia, it occurs, together with carbonate of lime, in enormous quantity in the species of limestone called dolomite. It most abounds in the ash of grains, contributing 12 or 13 per cent. of the same. In the ash of the remaining parts of cereals and of other plants, it varies from 2 to 4 per cent.

Phosphorus does not occur free in nature, but is generally to be found combined with oxygen and calcium. When prepared free, it is a yellowish semi-transparent, and waxy solid. It is exceedingly inflammable and oxidizable. It ignites on the slightest friction, whence chemists only keep it with safety under water. In the air it readily oxidizes, giving off white fumes, and in the dark emitting a pale lambent light. If slowly oxidized, its white fumes are the oxide P203. Upon its ignition the resulting oxide is P205,—phosphoric acid. Phosphoric acid may be considered as the most important inorganic constituent of plant life. Seeds have it in larger quantity, as it constitutes about 30 per cent. of the residual ash of grains. It is equally important in animal life, being a most essential constituent of the brain, nerves, blood, and bones.

Sulphur is found free in nature as yellow crystals. It is found combined too, with many metals, forming sulphides, —which are the ores from which the several metals are usually obtained. Again, combined with oxygen in addition to the metals, it forms the salts called sulphates. Sulphur, during the process of ignition, produces the oxide SO2, a colourless gas, soon intimating its presence, however, by inducing the sense of suffocation. SO3 is its principal oxide; which, combined with a molecule of water, is H2SO4, the important sulphuric acid. The amount of sulphur found in the ash of plants is inconsiderable, —over 1 or 2 per cent.

Iron.—Of the invaluable element iron, the appearance and main properties are presumably known to all. It is rarely met with naturally pure, save in the form of meteoric stones; but in the well-known form of wrought iron it is nearly quite pure. Although for minga very small percentage of plant ash, it is still most essential, and to animal life, as well as plant, several parts of animal bodies demanding it in abundance for their constitution. It forms three classes of oxides, the presence of two of which in the soil is of moment. These are (a) the ferrous, or proto-oxide, Fe2O2, and (6) the ferric, or per-oxide Fe2O3. As the symbol shows, the ferrous has less oxygen in combination; but when exposed to the atmosphere, it greedily. absorbs the additional amount of oxygen, which will constitute it the ferric oxide. Inasmuch as the latter, again, is easily divorced from the oxygen, in contact with other combinations in the soil, iron, it will be seen, discharges valuable functions there, as an oxygen contributor. It is iron also which imparts the variety of colour to the different classes of soil.

Manganese, prepared free, is a reddish-white, brittle, excessively hard metal, which the slightest exposure to the air oxidises. The oxide produced is MnO. MnO2, another of its oxides, is much used in the labortory for producing oxygen. The quantity of this element in plant life is very minute.

Chlorine is not found naturally free; but when produced free, it is a greenish yellow gas, pungently odorous, and most irritably injurious to the mucuous membrane. For hydrogen it has a strong affinity, the combination forming hydrochloric acid. Combining with the metals, salts are produced by it, called chlorides, of which the principal is chloride of sodium, or common table salt.

Bromine, Iodine, and Fluorine all resemble chlorine in their respective qualities, the four forming a detached group in chemical science. Bromine and iodine are almost entirely confined to sea-water and marine plants. Traces of fluorine are found in the blood, teeth, and bones.

Copper.—Minute traces of copper have been found in the ashes of animal and vegetable organisations, but it is not considered a necessary element in the economy of animal and plant life.

The absorption, accordingly, of these inorganic or "mineral " constituents by plants, is entirely effected from the soil, by means of their roots. Such constituents are present in the soil in many various combinations, some of them being almost insoluble in water. Rain-water, however, dissolves carbonic acid from the atmospheric air, and water containing it in solution, can dissolve compounds insoluble in it whilst pure and simple. Carbonate and phosphate of lime are thus rendered available for plant nutrition. It is believed that some indirect power is exercised by plant roots themselves, in breaking up the insoluble compounds in the soil.

The different combinations in the soil affording the necessary inorganic elements to plant life, and the various functions of the latter to whose operation such combinations are subjected, fall to be discussed in a subsequent chapter.

Chapter III.—Of Geology.

The student, in having his attention turned to the science of geology, cannot fail to be struck with the vastness of the field which is there opened out to research; and when he encounters undeniable proofs of our globe having endured through countless ages ere it became fitted to receive its present species of inhabitants, he more distinctly can realise the hopeless incomprehensibility of the word eternity.

Whatever the source of the sixty-three original elements, the greatest physicists are of opinion that when these became united in the mass, resulting in an independent planet, ruled by the sun's attraction, such a degree of heat must have prevailed therein, as to cause such elements to exist in the gaseous state. As the heat would depart by radiation into proximate space, the denser compounds would tend to unite as a congeries, so that when the earth had commenced its career of revolution around the sun, its consistence would be that of a pasty mass, enveloped with dense vapours and gases. Its present spheroidal shape would ensue upon its rapid revolution upon its own axis. With the process of cooling down would keep pace that of the condensation of its surrounding fogs and gases into air and water, whilst its more solid mass would concentrate in bulk, pressing inwards towards the centre of gravity with the attendant effect of irregularity of surface, caused by the absence of a uniform degree of internal resistance to such external pressure. With the increased intensity of this pressure, more marked would become mountain and valley. Moreover, the resisting force of the internally confined fluid substance would gradually prevail over the weaker portions of the crust, and its upheaval, with all the violence of earthquake and volcanic convulsion, would vastly exaggerate the superficial irregularity of Moses' " dry land." Thus did it appear above the face of the waters, but naked as yet,—sterile, without soil, entirely devoid of living organisation. Then gradually atmospheric action would crumble down those bare rocks exposed to its action. The detritus washed into the surrounding depth of waters, there subjected to the superincumbent pressure for epochs of time, became solid strata or layers, thence to be upheaved and exposed to the atmospheric process, as a rock-forming material different in nature and texture from its originators. And so on, the alternate depression and upheaval continues even to the present time, but in an infinitesimally less degree, for the cover of vegetation over the larger portion of the earth's surface protects from the erosive action of the atmosphere, and earthquakes are less frequent, and the more considerable volcanoes for the most part inert. By the earth's crust is meant the thickness of it which has come under the cognisance of geologists, and it bears an inappreciable proportion, of course, to the earth's diameter. Heat increases in the ratio of our depth of penetration through the crust, proving the immensity of heat still present within our globe, which is conjectured internally to be in a molten state, or at least in a honey-combed condition, with molten matter filling the cells. This is evidenced by the phenomena of lava and hot springs, even more strikingly than by the large increase of temperature in deep artificial mines. The rocks, —and this term includes clay, gravel, and sand deposits,—which compose this crust, are divided into—1st, The igneous, being those formed by the agency of fire, or from fused melted matter, and preserving their original condition; 2d, The aqueous or sedimentary, comprising such as have been formed by the deposit of detritus of rocks exposed to the air, and laid down under the water in regular strata; 3d, The aerial, or such deposits as have been accumulated by atmospheric agencies. Sand dunes, calcareous sands compacted by rain, the debris at the bottom of cliffs, and soil are examples; 4th, The metamorphic, those which have undergone change of texture since the eruption or deposit of their constituents. Traces of organised remains begin to be met with in the earliest aqueous rocks, and thus attain a higher development in proportion to our ascent to the latest aqueous deposits,— stratifications,—till it becomes perfect as that of the living forms, both animal and vegetable, now existing. The branch of geology dealing with such traces, or fossils, as they are called, testifying to the forms of life co-existent with the deposition of the specific materials of the strata where they are found, is named Palaeontology—an abstruse study, its prosecution demanding the preliminary of a highly scientific training.

The igneous rocks principally exist as granite and trap. They are chemical productions, i.e., have been consolidated from fusion by chemical means. Besides forming the solid framework of the earth, and the foundation of the other rocks, they are upheaved, and constitute the principal mountain chains, and they are exposed in masses of enormous area. They are also poured out in profusion as lava and scoriae during volcanic action, and they permeate the rents and crevices of the sedimentary rocks. All igneous rocks are composed of minerals, silicates, to wit, i.e., salts formed by the union of silicic acid with a base. These silicates are divided into two classes—silicates of magnesia and silicates of alumina ; and the various subdivisions in each are constituted by so many mixtures with silicates of potash, soda, lime, iron, manganese, &c. The uncovered masses of igneous rock generally being situated at high altitudes, the soils they form are at such an elevation as to be incapable of cultivation, and they are accordingly left in the natural condition. But when such soils exist in practicable situations for the agriculturist, or the detritus of them is conveyed thither, great fertility obtains, and the soil is easily worked. This is specially predicable of soils derived from trap rocks.

Metamorphic rocks are produced by the alterations effected by heat in the texture and structure, and by its rearrangement of the atoms of the constituents of their originators. Although resulting from the changes in strata of all epochs, still they, for the most part, lie over or against the huge igneous masses, being comprehended in the so-called Laurentian, Cambrian, and Silurian eras of formation. Together with the igneous, they constitute the principal part of wilder Wales and the Scotch Highlands; and whilst such tracts admit of little cultivation, they are admirably suited for sheep runs.

The stratified rocks have been produced mechanically, as we have seen, by the agency of the atmosphere and water; chemically by the precipitation of their constituents from solution in water, e.g., rock salt; and organically by the agency of organised living structures, e.g., coal and peat, both of which are the remains of plant life, and limestone, the remains of minute animalculae. Stratified rocks have a threefold classification, denoting the epochs of their respective formations, viz, the Primary or Palaeozoic—ancient; Secondary or Mesozoic—middle; and Tertiary or Cainozoic—modern. The expression primary; signifies no fixed era or standpoint of time,—merely that indefinite portion of the past when the first sedimentary rocks began to be deposited beneath the water. By " era," too, the geologist understands any period comprehending groups of living organisms bearing points of close resemblance to each other. The names given to the different formations have generally been taken from that of the most characteristic or useful rock in the group, which may sometimes include a stratum of quite an opposite texture and composition. Thus the old red sandstone formation includes some of the densest clay rocks, and it may appear contradictory to apply the term sandstone, clearly suitable in one district to the clay slate of another. But as these two contain the identical class of fossils, their similarity of age is demonstrated, and hence the justice of their sharing the same family appellation.

The stratified rocks are arranged in the following leading groups, in order of time:—

I. Those of the Primary or Palaeozoic period, including

(a.) The Laurentian or Pre-Cambrian era rocks, which are principally composed of gneiss, a metamorphosed granite, whose original granite particles have been disintegrated and redeposited, and compacted with a different structure and texture.
(b.) Cambrian era rocks, composed of grits, slates, and conglomerates.
(c.) Silurian era, divided into (1) lower, comprising the Lin-gula Llandeilo, and Caradoc beds, and (2) the upper division, comprising the Llandovery, Wenlock, and Ludlow beds.
(d.) Devonian and Old Bed Sandstone era, comprising the lower, middle, and upper Devonian beds of England, and the like three Old Bed Sandstone beds of Scotland.
(e.) Carboniferous.—Carboniferous or mountain limestone, millstone grit, and the coal measures.
(f.) Permian—the lower, containing red marl, sandstone, and conglomerate, and upper containing lower and upper mag-nesian limestone.

II. Secondary or Mesozoic period, containing

(a.) Triassic, or New Bed Sandstone, of lower, middle, and upper formations.
(b.) Jurassic era, embracing Lias (lower, middle, and upper); Oolite, lower—inferior oolite, fullers' earth, great or Bath oolite, forest marble; middle—Oxford clay, coralline oolite; and the upper—Kimmeridge clay, Portland and Purbeck beds.
(c.) Cretaceous era—Hastings sand, Weald clay, lower green-sand, gault, upper greensand, chalk marls, and chalk.

III. Tertiary or Cainozoic period, including

(a.) Eocene era—lower, middle, and upper,—the lower including plastic and London clays, and the middle and upper the deposits formed in estuaries.
(b.) Miocene era—Lignites and leaf-beds.
(c.) Pliocene era—Crag formations.
(d) Pleistocene or post-tertiary era, comprising boulder clay or glacial drift, raised sea beaches, fens, peat bogs, river deltas, alluvium, sand dunes, and so on.

These main groups, and, with a few exceptions, the various strata they respectively comprise are all represented in the British Islands,—an evidence of the extensive convulsions they have undergone.

Although in few countries do they observe such an unbroken series, still they invariably observe the cardinal order of deposition, whatever hiatus may occur in it. Periodic convulsion throughout immense areas is evidenced by the existence of fossils of land plants, which flourished on the soil of certain strata, being discovered beneath immense stratification of a different class. To the variety of the British rock formations are due the multiplicity of its types of natural scenery, its many different modes of agricultural practice—all included, too, within so small a superficies. This variation in practice is a consequence of the variety of soil, which, as a rule, has a direct relation to its underlying rock formation. By the term "soil" is understood so much of the surface as in cultivated ground comes under the operation of the plough, and which in land still in a state of nature would come under such influence were it to be cultivated: "subsoil" is what comes immediately under it. Where identity of chemical constituents does not exist between the soil and its subjacent rock formation, the constituents of the former have been imported from another source. But in all cases, rock and subsoil alike have an important bearing upon the questions of facility of drainage, the physical features of exposure, flatness, or declivity of the soil.

As already mentioned, the soils of the Laurentian, Cambrian, and Silurian eras are mostly found at a high elevation; and, in addition, being for most part of a poor description, are seldom cultivated with any degree of success. On the other hand, those of the Devonian and its companion series possess all degrees of value.

In the Carboniferous era, the soils of the coal measures groups are inferior, and generally much neglected; those of the millstone grit are also poor and thin. In the mountain limestone group, they are classed as of medium quality; and, as in Derbyshire", they afford good pasture ground. In the Permian, the soils are of a light, dry description, and easily cultivable. As the name implies, most of its limestone holds too much magnesia for agricultural purposes. Of the Triassic era, the soils are variable. They are kept under pasturage, over the marls, and are then good for dairy purposes. Above the sandstones they are deep and dry, although not of high quality. In the Jurassic, they range from the densest quality, such as, e.g., Lias, Oxford, and Bradford stiff clays, to that of a thin light sandy type. Excepting those above the chalk marls, the gaults and wealden clays, the Cretaceous affords soils of a light dry nature, which produce, under pasturage, an excellent herbage, sweet and nutritious, and well adapted for sheep stock. Coming to the Eocene era, we find such dense soils as the London clay, with others of a lighter description in immediate contact with them. In the Pliocene, we encounter the soils typified by the rich alluvium of river-side deposits—the "carse", lands of Scotland, deltas; and also meet fens, peat-mosses, and land reclaimed Dutch-wise, from the sea.

In districts where the subsoil is deep, and a considerable space intervenes between the upper soil and its underlying rocks, there is generally a scarcity of stones for building or road-making purposes; and this is especially the case in clayey formations, and those of the Pleistocene era. The clay, however, can be burnt into bricks, and material in substitution of road "metal"—which latter, however, is a poor make-shift for stone. The nature of the subjacent rocky formations too has considerable influence upon the question of water supply. Thus the numerous fissures in the chalk and oolite formations act as natural main drains throughout large areas, intensifying the droughts of hot summers. The opposite extreme is reached when rocks or subsoils are of a close or retentive description, unfavourable to the percolation of water. Hence it is that a knowledge of the position and nature of the subsoil and underlying rocks is essential in the conduct of extensive drainage works. The term "dip" means the inclination of strata to the earth's centre, and is measured by the angle formed by the intersection of the plane of the horizon with the plane of the beds themselves. "Strike" means a line at right angles to the dip. "Outcrop " is where the beds appear at the surface. By rock "structure" is meant the peculiar arrangement of its component parts in the mass, e.g., stratified or columnar structure (like that of the igneous rocks of Staffa and the Giant's Causeway.) "Texture" implies the minute arrangement of the composing particles; and "compositions" applies to their chemical features. "Joints" are the lines of fracture seen dividing rock masses into separate lumps or blocks, and which facilitate the quarrying of them. "Faults" are such fractures of the strata series as raise or depress the level of the strata on one side of such faults above or below that of the strata on their other side, and thus break the continuity of stratification.

Chapter IV.—Of Botany.

Of the science of Botany, physiological botany is that one of its departments which most concerns the practical agriculturist, treating, as it does, of the different organs of plants, and their respective functions. The classification of plant life is a field of study too extensive for his time and opportunities. But as all the British cultivated plants are included in a very few "orders," the comparative slightness of their physiological variations renders his acquisition of this branch so much the easier by its approximation to a uniform applicability.

A normally developed plant consists of four different organs, viz., root, stem, leaves, and flowers,—the first three being nutritive organs, and the fourth that of reproduction. They are alike modifications of one structure, for the fundamental structure of all plant forms is the simple cell. Cells are minute, round, bladder-like vessels, which cohere and form cellular tissue, named parenchyma. They have their origin in a thin mucilaginous compound called protoplasm, which is considered the seat of life. A small germ, termed a nucleus, appears in the protoplasm, which presently, with some of the protoplasm, gets enclosed by a species of sac or covering, and this constitutes a cell. Increasing, the nucleus seems to be divided, and the cell-wall closing round either portion, forms two distinct cells. And so on indefinitely. This cell-wall or envelope is formed of a substance termed cellulose, the composition of which will be subsequently given. Active cells, besides containing protoplasm and nuclei, for the purposes of increase, and also their several characteristic contents, have, when situated at the exterior portions of plants, chlorophyll as well, which is their green colouring matter, and has the property, when it is acted upon by sunlight, of assimilating certain elements from the atmosphere. The shells of nuts and other seeds are composed of hard solidified cells; the roots of turnips, potatoes, &c, almost entirely of juicy cells. The cell-walls or coverings of different plant groups have characteristic marks, whether dotted, barred, reticulated, or with spirals or other quaint devices. Cells cohere by means of connective tissue, supposed to be secreted from their walls. " Intercellular" canals are the spaces formed where cells do not adhere on all sides ; and they serve for circulating air through the plant structure. Fibres and vessels are formed by the modification of simple cells. The former appear to be formed of elongated cells, which have been filled up with woody substances. These firmly cohering, form woody fibre. The cells of vessels are not thickened or filled up. They are formed by strings of cells, so to speak, having their contiguous partitions destroyed, so as to form a continuous tube or channel. They possess the distinctive markings of the cells, whence they are derivative. Their office would appear to be that of promoting not sap but air circulation in plants. Cells constitute the entire formation of some plants, such as fungi, mosses, and sea plants; and these are termed cellular. They have no flowers, and propagate by means of cellular germs. The remaining plants are called vascular, as they contain vessels, fibres, and cells. Excepting the fern tribes, they have flowers more or less conspicuous, and they are reproduced by the instrumentality of true seeds.

A cellular skin or covering, called the epidermis, extends over every part of the plant. It is divided into the cuticle or outer portion, and the derma or inner portion. The cells composing it are colourless, but through them shines the chlorophyll contained in the cells underneath. When examined by aid of the microscope, on its surface are seen oval-shaped organs with small openings in their centres leading through the epidermis into air chambers. These openings are called stomata, and serve for the purposes of perspiration and exhalation of liquids and gases. They are found on all parts of the plant above ground, excepting the petals or coloured portions of the flower, and they seem to possess the power of opening and closing according to the moist or dry condition of the atmosphere. The epidermal cells get modified to assume the form of hairs and scales, as seen on leaves and other parts of certain plants.

Selecting the root as the first organ for consideration, the student must make its acquaintance as the "descending axis" of botanists. It is the seed's primary development, and always has a downward direction. This delicate process branches into numerous fibrils, whose number and dimensions rapidly increase. "Radicle hairs" are scattered over them, and through these and the cells of the more delicate parts of the fibrils' epidermis is absorbed the plant's nourishment from the soil. The elongation of roots proceeding from their extremities, they are fitted to penetrate in every direction in quest of suitable food. This organ's development assumes a great diversity of form. Of species, we have terrestrial roots, such as have been already described,—though it may be remarked that the roots of fungi, as in the case of sea-weeds, merely serve for anchors, the fungus obtaining its food from the atmosphere; aquatic roots, belonging to floating plants, which are unattached, floating freely in the water, and absorbing nutrition from that medium, e.g., duck weed; aerial, as in the family of orchids, which in the tropics are attached to foliage, and their roots hang in the air, whose moisture they absorb, and against the branches, whence they derive food from the tree's decay; and parasitic, those fastened to the substance of other plants whose sap they absorb, and they have no direct connection with the soil. Such are moulds, the dodder, injurious to clover, and the festive mistletoe.

The root functions accordingly are, with exceptions to fix the plant, to absorb nourishment from the soil, and occasionally, as in the turnip, to serve as a magazine of nourishment for the plant's use in promoting its growth at a future season. The absorbent cells of roots would appear to possess a power of selection and rejection over suitable and injurious food constituents. The absorbtive process is considered to be that of endomosis, which signifies the property of gases and fluids, enabling them to pass through certain membranes in order to mingle with other fluids and gases possessing different densities and compositions. "Exosmosis" expresses the converse process.

The stem is the organ which bears the leaves and flowers; and, like the root, it assumes all possible phases of modification. Some stems are long, others short, so as to be scarcely seen above ground; some burrow to a varied extent under ground; whilst others again, for support, have to cling to stronger neighbours; familiar specimens, whereof respectively are ordinary trees and grain plants, the turnip, the quicken grass and potato, and ivy. The tuber of the potato is in fact a stem, its eyes the buds, producing branches and leaves. Stems are divided into three great classes, viz., exogenous, endogenous, and acrogenous. A stem of the first of these divisions increases in diameter by the addition of matter to its outer circumference. A cross section shows in its centre the pith, with lines radiating from it to the circumference or bark, which are called medullary rays, and concentric rings round the pith, each marking a year's growth. Outermost is the bark, easily separable from the wood proper. The annual increase to wood and bark takes place immediately under the latter in a layer of slimy substance termed the cambium. The outer and newer wood is called the laburnum, the inner or heart-wood, which is denser, generally of a darker colour, and through which there is less sap circulation, is named the duramen. The bark has three layers,—the innermost tough and fibrous, forming in some plants, e.g., flax, "the bast."

An endogenous stem increases in diameter by the collection in its cellular centre of bundles of fibres and vessels, which swell out and extend the outer circumference. In a cross section we see no pith, no concentric rings, no true separable bark, but on the contrary, a hardened cellular mass of bundles of vessels and an internally hard inseparable bark. These fascicles of fibres run from the bark inwards and downwards towards the stem's centre, effecting a firmly interlaced structure.

The increase of an acrogenous stem takes place at its summit, as exemplified in the case of ferns and tree-ferns. The whole length is of nearly the same diameter, it is marked on the outside by the scars of leaves, whose bases, indeed, compose it. In cross section there appears a cellular mass, often hollow in the centre, with bundles of vessels interspersed throughout. Stems produce buds, or branches bearing them ; in some cases only at their extremities, "terminal" buds, in whose destruction is involved the death of the plant; in other cases, both terminal and lateral. Some buds, instead of developing into branches, become modified into thorns. Both branches and thorns have a continuity of the central stem-substance, and are thus distinguished from such prickles as, e.g., the briars, which are merely developments of the epidermis, having no direct connection with the stem. The functions of the stem are chiefly to support the leaves and flowers, and to afford them a due exposure to the influence of sun and air. The modifications of leaf form are endless. Microscopically examined, the leaf epidermis shows numerous hairs and stomata. Immediately beneath it are discovered elongated or "palisaded" cells, having a close vertical arrangement; and spaces are numerously interspersed, corresponding with the stomata above. Inferiorly occur other cells more freely and openly arranged, with the fibres and vessels constituting the veins of the leaf running through them. The arrangement of leaf-veins— the venation of leaves—affords another means of plant classification. Along with exogenous stems, plants have a reticulated venation:—with endogenous, a herring-bone, venation, or the veins running parallel from the central vein to the leaf's margin. The petiole or leaf-stalk attaches it to the stem. On any ordinary tree it is more or less round and fibrous; in the rhubarb plant again, it is thick and juicy, and constitutes the edible part. Sometimes it has almost the identical functions of the leaf itself; in sundry pines there is no distinction. The functions of the leaf are occasionally assumed by the stipules—small leaflet-like bodies at the base of the petiole, and very apparent in rose, pansy, and clover plants. Frequently they form tendrils and sheaths of the petiole. The midrib or central main vein of the leaf is a continuation of the petiole.

Leaves are either simple or compound,—the former when the petiole carries but one blade, and has no joint above the point of union with the stem. Such are the leaves of the oak or beech trees. Compound leaves' have their blades subdivided into separate distinct lengths, each of them being articulated to the petiole, as in the case of the horse-chestnut. Leaf margins may be entire, serrated, crenate, and so on; the blades, according to the apex, acute, obtuse, &c. When divided laterally from margin to midrib they cleft pinnately; longitudinally, they are pal-mately cleft, and so forth.

Vernation is the varied mode of the folding up of young leaves in the bud. The attachment of leaves to stem is spirally arranged in a strict mathematical order. There is the like analogy between branches and stems, rootlets and root. Certain plants lose their leaves annually, others retain them permanently. Of the first division, the leaves of some wither and fall away on the completion of bud formation. Such plants are called deciduous, as oak and ash trees. Of others, the leaves wither and decay, but still adhere, as do those of lilies. Plants of the second division retain their leaves of one season's growth till the full development of their successors in the next; the majority of our evergreens for example. When their functions have been nearly discharged, leaves change their colour, and from the secretion of inorganic matter in their cells, they shrivel up. Simultaneously, a constriction of the base of the petiole becomes gradually complete, whereupon all the cells of stalk and leaf die, and the latter falls to the ground.

Leaf functions are analogous to those of the lungs. Leaves seem to expose plant sap to the action of air and light, which frees their juices from excessive moisture, and. induces such chemical changes of their substance as elaborate them into suitable compounds for assimilation by the plant, to the end that in all its parts cell-building may multiply.

In certain plants the leaves are possessed of strange supplementary powers. For instance, the leaf of Venus's fly-trap has the property of curling inwards and enfolding the luckless insect which may have alighted thereon. And stranger still, this duress is effected from a carnivorous propensity; for physiologists declare that the plant thereupon absorbs the juices of the insect for its own nourishment. In the pitcher plant some of the leaves act as watertight reservoirs, by assuming the form and direction best suited for receiving the supply of moisture; and frequently they contain a considerable supply of water. The large quantity of fluid containing solid and gaseous bodies in solution, and absorbed by the delicate cells of roots, has an upward current through the central portion of the stem, and reaching the leaves, where it undergoes the changes adverted to, it next takes a downward current through the interior parts of the stem, delivering growth materials through its course.

The belief at one time was general of the excretory power of roots over plant waste and matter injurious to its health; but it has been surrendered by contemporary physiologists. The absorbent and exhalent power of plants over moisture has, it will be seen, an important influence upon the passage of water from soil to atmosphere, when the immense extent of forest area throughout the world is considered. Much of it, however, is retransferred to the ground, having been condensed on the colder leaf surface by warmer air currents. The wholesale hewing down of forests has been observed to produce a scarcity of rain in regions where no such privation existed while the forests flourished. Plants by their green colouring matter act as purifiers of the air by absorbing carbonic acid, so hurtful in excess to animal life. This process is accomplished by such colouring matter when subjected to solar action, decomposing the acid, and whilst freeing the oxygen, assimilating the carbon.

A flower when normally developed consists of four parts—two called the enveloping organs, viz., the calyx or outer circle, and the corolla or coloured portion, and the remaining two called the essential organs, as being necessary for the production of seed, and named respectively the stamens, and in the centre the pistil. All parts alike are modifications of the leaf. The leaves forming the calyx are named sepals; those of the corolla, petals ; and in each they occur, either united or separate, and assume infinity of shape. The stamen consists of a stalk or filament, frequently so short as to make it appear absent, which supports two bags called anther lobes, these containing a dust powder—the pollen of the flower, necessary for the fertilising of the ovules or germs of the embryo, and these are held by the pistil or ovary. Above this last is the style or stalk, having at its extremity the stigma, upon which the pollen must be deposited ere it can come into contact with the ovules. The changes in the bean flower may be taken to illustrate the stages of the reproductive process. The grains of pollen on the stigma extend minute processes down the style into the ovary, where, coming into contact with the ovules, fertilisation ensues. Next the calyx, corolla, and stamens, having performed their functions, wither and die. The pistil or ovary is now disclosed, as having assumed the shape of a pod, and within it the fertilised ovules have developed into a row of beans or seeds. The plants of some varieties have staminate or male flowers on some of them; pistillate or feminine flowers on others Others bear both sexes on one and the same plant; whilst the generality bear flowers containing both stamen and pistil together, and these are called perfect flowers. The various modes of fertilisation in plants is an interesting study; and the unlikely agencies through which the access of pollen to the ovules is effected bear evidence of the highest design. Insects have a great share in this office, through the adherent pollen on their legs and bodies getting deposited on the stigmata of the successive flowers upon which they alight. Indeed, it is maintained by the most eminent savants that the primary office of the many bright hues, varied scents, and tasted secretions of flowers, is to allure the visitation of the insect tribe for the purpose of pollen transportation. The wind also carries many kinds of pollen dust to its due destination.

To enter upon the consideration of the countless different conformation of parts, relation as to numbers and modes of arrangement of the flower, would be to transgress the limits of this manual.

The seed, then, is the fertilised matured ovule. It contains, along with a new plant in embryo, a supply of nutriment for its sustenance when it begins to germinate, and before it can derive that from the soil direct. The embryo consists of the radicle, or root rudiment, the seed leaves or lobes called cotyledons, and the plumule or young stem. The number of cotyledons affords yet another standard of plant classification. Exogenous stemmed plants have two cotyledons in their seeds, and hence are called dicotyledonous; endogenous, only one, and are therefore styled mono-cotyledonous; whilst flowerless plants which have no true seeds, and consequently no cotyledons, are named acotyledons. In the pea and bean the supply of nutrition is incorporated with the cotyledons; in grains it is quite distinct and separate from them. In the former the cotyledons remain beneath the surface, and are absorbed by the radicle and plumule. From the turnip seed the two cotyledons spring above ground, appearing as two smooth leaves, and only decaying when the rough leaves proper sprout and develop. It is with these tender cotyledons that the turnip beetle or "fly" works such havoc, consuming them and thereby arresting the seed functions. All grasses and grains are monocoty-ledonous. The principal food ingredients stored up with the embryo in the seeds are starch and nitrogenous and phosphatic compounds. The absence of direct light and the presence of air and moisture are necessary for the germination of the seed. The air and moisture are requisite for effecting chemical changes essential to germination; the latter softens the seed constituents, and with the oxygen in contact the atoms change places, and soluble compounds are formed. Those are absorbed by the cells of the embryo, its several processes are developed, and the rudiments of root and stem produced.

The complicated bodies,—called the proximate constituents,— elaborated and organised by plant life from the simple inorganic compounds derived from soil and atmosphere, are classified into three divisions, according to the different kinds of nutrition these subserve in the animal body. The three divisions are as follows: the Amylaceous or Saccharine, Oleaginous, and the Albuminous. The first group is entirely composed of carbon, hydrogen, and oxygen, the two last entering in the exact proportions requisite to form water, whence they are often termed carbo-hydrates. In Roscoe's Chemistry they are arranged under the heads of Sucroses, C12H22O11, represented by sucrose or cane sugar; Glucoses, C6H12O6, represented by dextrose or grape sugar; and Amyloses, C6H10O5, represented by dextrin, starch, cellulose, and gum. The amyloses are insoluble in water, but the action of certain acids converts them into dextrose, which is soluble in water; although not to the same extent as is sucrose. Gum and cellulose are with difficulty converted into dextrose; starch, less so. Starch, however, soon assumes a soluble form under the action of the saliva and other juices of the body. The action of the organic compound diastase, which is always found present in seeds beginning to germinate, renders starch stored up in the seed soluble for the use of the embryo at that stage. The starch first assumes the properties of dextrin, and then it is readily changed to dextrose. It will be noticed that the addition of one molecule of water to those of the third division will make them assume the same formula as those of the second.

The composition of the oleaginous compounds is the same, but with the amount of hydrogen much in excess of the proportion necessary, with the contained oxygen to form water. Consequently, they are styled hydro-carbons. Glycerin, C3H8O3, is the base of all fatty compounds, which vary with the different proportions of acids in combination with it. Most fats and oils contain a mixture of all these. The three principal acids are— palmitic, C16H32O2; oleic, C18H34O2; and stearic, C18H36O2.

The albuminous compounds contain nitrogen, carbon, hydrogen, oxygen, phosphorus, and sulphur; they are also called the nitrogenous compounds. The composition of them all varies but little; and they are convertible by a slight rearrangement of atoms. These compounds are derivable by animals only from vegetable sources. They are assimilated without undergoing much alteration; and in the animal constitution have almost the identical composition as the relative compounds in plant life. The following table shows the composition of the principal members of this group which are met with in the animal body:—

Albumin and fibrin abound in blood and muscle. The glutin of wheat corresponds to fibrin; and albumin is found in the juices and seeds of plants. Casein is the albuminous compound altered the functional action of these plants that in their first season's growth they do not develop flowers and seed, but store up a sufficient supply of nourishment in the hypertrophied parts for the basis of flower and seed growth during the following season. The rape and cauliflower plants are likewise descendants of nearly related stock: the abnormal development being seated in the leaf-stalks and leaves of the former, and in the flower-stalks of the latter. Varieties are producible by means of the artificial fertilisation of the seed of one plant through the application of pollen taken from the flower of some other particularly developed plant of the same species. In this way has been produced the countless varieties of wheat, barley, oats, and other cultivated plants. Hybrids can also be produced by fertilising the ovules of one species with pollen from the flower of another species. But, in common with the hybrids of the animal kingdom, these are incapable of reproduction.

All the grains and grasses of our annual crops belong to the order Gramineae, which is one of the class Endogenae; wherefore they are all endogenous stemmed, and their seed embryo is mono-cotyledonous. Wheat forms the genus Triticum; barley, Hordeum; oats, Avena; rye-grass, Lolium; and so on.

These genera are respectively subdivided into several species ; these again into innumerable varieties. The bean, pea, and clover plants belong to the order Leguminosae, of the class Exogense; and have therefore exogenous stems, and are dicotyledonous. The bean plant constitutes the genus Faba; the pea, Pisum; and the clover, Trifolium. To the class Exogenae also belong the turnip, rape, cabbage, kohl-rabi, and wild mustard plants, which with others constitute the order Cruciferae, with its genera, species, and varieties respectively.

Chapter V.—Of Animal Physiology.

There are many striking points of analogy between animal and vegetable physiology. In point of fact, when we look at the elementary organisations in each great natural division, the boundary line between them is difficult to be drawn; and the forms are numerous, regarding which it is matter of debate as to which great division they properly belong. As we ascend to more highly-developed forms in either, the line of demarcation becomes more readily definable. The highest forms of plant life possess no nervous system, no cavity for the reception and digestion of solid food, in other words, no stomach ; and they have no independent power of locomotion ; all of which qualities, on the other hadd, belong to the higher forms of animal life. Another cardinal distinction is that whilst plants can assimilate the elements necessary for building up and maintaining their structrue from such simple or inorganic compounds as carbonic acid, ammonia, and nitric acid, animal bodies, on the other hand can derive them from such complex organised compounds only as are formed by plants out of the simpler elements. This prepares us for the important fact, that all the actions of animal life consist in the liberation of heat or force attendant upon the disorganisation of the organic compounds forming the tissues. Consequently, every movement of the animal implies a consumption or using up of materials in its frame. Muscular action is the contraction and expansion of the delicate fibres composing muscle structure in obedience to nervous stimulus; and such contraction is caused by a liberation of atoms or molecules, and the resulting disorganisation or breaking up into simple compounds of the proximate substances composing the muscle fibres. Plants prepare their proximate constituents from the simple inorganic compounds by sun heat and light agency; whilst animals derive their possible existence from the liberation of latent force when these organised compounds are broken up. Plants also absorb carbonic acid and give off oxygen; animals inhale oxygen and exhale carbonic acid.

Nevertheless there are to be met with in the lowest scale of development forms of animal life devoid of stomach, nervous system, and independent locomotion; and also vegetable forms endowed with some degree of locomotion, and organs functionally resembling the stomach, and which do not obey the plant laws of exhaling pure oxygen and subsistence upon inorganic compounds.

As in the vegetable, so in the animal kingdom is it with regard to the fundamentally structural nature of the simple cell, created from a nucleus and the organic compound protoplasm by that mysterious agency hitherto only known and defined as "vital force."

The functions treated of in animal physiology come under the three heads of Nutrition, Reproduction, and Correlation, which last includes the consideration of the functions of sense and motion, or those by which the total organism is brought into relation with external nature.

Beginning in order, we find in all the more highly-developed classes an alimentary canal, into which is received food material, undergoing those processes which render it fit for assimilation. Then it is passed along the tortuous channel, where its nutritive elements are absorbed and thence conveyed to the blood, and at whose extremity the residuum of indigestible matter is excreted. The solid food when received into the mouth is broken up by the teeth, and mingled with saliva during mastication; and thus rendered into a pulpy mass easy to be swallowed, and prepared for stomachic action. Besides softening the food the saliva exerts certain chemical influences upon it; notably converting insoluble amylaceous bodies into soluble saccharine bodies. The mass passes through the gullet, entering the stomach at the cardiac orifice. There it is acted upon by several secretions, the principal of these being the gastric juice, whose properties closely resemble those of hydrochloric acid. When the various compounds are nearly dissolved, they are passed on through the pyloric orifice of the stomach to the intestines in the condition called chyme. Chyme is a pasty substance, containing dissolved saccharine matter and undissolved starch, albuminous bodies broken up and wholly or partially dissolved, oleaginous bodies broken up but undissolved, such solid indigestible portions as have been enacted upon by the gastric fluids, and some of the liquids swallowed along with the solid food. The intestines, according to their diameter, are divided into the large and small. Continuing from the stomach, the small intestine is nominally distinguished as the duodenum, jejunum and ileum; and the large intestine as the caecum, colon, and rectum. The latter distinction is less merely nominal, the rectum being less puckered or convoluted than the other two. At the union of large and small intestines occurs the ileo-caecal valve, allowing a passage but one way from the small to the large.

Ere the chyme has entered far into the duodenum it is subjected to the action of the intestinal juices organised in various glands. Chief are the bile and pancreatic juices, secreted by the liver and pancreas respectively. These serve further to dissolve the albuminous compounds, of emulsifying or saponifying the oily constituents of the chyme, and of recommencing the conversion process of starch into sugar, which had been arrested by the gastric fluids. And thereby all are alike rendered capable of direct absorption. The chyme continuing its course through the intestines, has its available compounds absorbed and carried to the blood, and the insoluble, indigestible residue voided from the rectum.

At this stage it may be as well, before adverting to the processes of absorption and nutrition, to consider the constitution and circulation of the blood.

Like the sap of plants in its grand work of supplying all the animal tissues with the necessary food for health and maintenance, it has to discharge the additional functions of keeping up the animal temperature in every part, and of removing waste tissue substance and matter deleterious to life. Actually it consists of a colourless fluid containing innumerable minute globules,—"corpuscles,"—the greater part of which are red in colour, and give the blood its characteristic hue. Its fluid portion, the liquor sanguinis, is composed of the "serum," holding fibrin and other compounds in solution. The fibrin exposed to the atmosphere has a tendency to coagulate, whence blood clot. In the first stage of coagulation its total constituents appear as one jelly-looking mass, but in a little the serum oozes thence as a yellowish slimy fluid. The corpuscles, however, remain contained in the fibrin. The serum contains about 8 per cent. of albumen, and with the exception of the fibrin and the corpuscles, the whole constituents of the blood. Roscoe gives the following graphic formula as the average composition of the blood:—

The heart, by its continual alternate muscular contraction and expansion, keeps up an uninterrupted circulation of the blood through the whole animal frame. There are four cavities in the heart, two auricles and two ventricles. At either side of the heart respectively are an auricle and a ventricle. The auricle of the left side opens directly into the ventricle of the same side. And so is it at the heart's right side. But the whole course of the circulation intervenes between right and left auricles and ventricles respectively. The contraction then of the left auricle filled with blood forces it into the corresponding ventricle, which, at the same time, expands in order to receive it. Next, the contraction of the left ventricle throws its contents into the main arteries, forcing it along them into all their branches throughout the body, and into their capillaries as well—the minute vessels closely interlaced, which permeate all the corporeal tissues. From these delicate tubes the blood enters the veins, and through them is forced back to enter the heart's right auricle; whereupon is completed the systemic circulation, or that whereby every part of the body receives an unfailing constant supply of nutritive blood.

As in the former instance, the right auricle pumps the blood into the right ventricle, whence it enters the pulmonary artery, and through it the lungs. In the lungs it is exposed to the action of the atmospheric air which they inhale, and having undergone the consequent important change of constitution it passes next into veins communicating directly with the left auricle, having thus completed the pulmonary circulation. The vessels leading from the ventricles are arteries; into the auricles, veins. Both orders of vessels are connected by means of the delicate capillaries so as to form a continuous channel. The blood is kept circulating in one direction by means of the valvular arrangement, which prevents the backward impulse when the auricles and ventricles contract. Blood suitable for the demands of tissue supply is the arterial blood only; when that function has been discharged it becomes venous blood. Thus the blood in the veins leading from the pulmonary circulation to the heart, and thence to the systemic capillaries, is arterial; the blood flowing into the right auricle, and thence through the right ventricle to the lungs, is venous. Arterial blood is of a bright scarlet hue; venous, dark purple. For which difference the reason would appear to be that, whereas the colouring matter, which contains a large proportion of iron, is fully oxidised in the case of arterial blood, in venous blood, on the other hand, it has parted with much of its oxygen during its passage through the capillaries into the veins.

Blood absorption consists in the taking up and conveyance of new material to supply the continual wants of tissue waste, and, in addition, the removal of this waste, which otherwise would effect the destruction of the parts throwing it off. The other absorbents besides the blood-vessels are the lacteals and lymphatics. The lacteals are confined to the intestinal canal; the lymphatics are distributed through all parts of the body where the presence of blood-vessels occurs. Both alike are connected with and pass through the lymphatic glands, which are supposed to have the power of further organising the compounds absorbed by the vessels. The absorption of substances received into the alimentary canal is effected by the blood-vessels and lacteals. Blood-vessels absorb all soluble matter, whether albuminous or saccharine, &c, directly through the enclosing membranes of the vessels. Hence, fluids and matter in solution can be absorbed by the blood-vessels before the passage of food from the stomach. The other two sets appear to have an affinity for particular substances. The lacteals chiefly absorb oleaginous substances, and their contents are then called chyle. In the intestines are numerous processes called villi, consisting of a network of minute blood vessels surrounding one or more lacteals, and all covered with mucous membrane like the other portions of the intestinal canal; and here it is that absorption principally takes place, although it does so more or less at all parts, even to the canal's extremity. It is still matter of doubt and conjecture as to the exact source whence the lymphatics directly absorb their contents. They are supposed to absorb the excess of liquor sanguinis effused for nutritive purposes by the delicate capillaries into the tissues, and also such compounds resulting from tissue changes as are not totally excrementitious, but capable of further utilisation and absorption, after they may have been more highly organised and again carried into nutritive circulation, The nutritive substances being almost entirely absorbed by vessels leading into the veins, they are conveyed through several organs, which elaborate them into various compounds capable of being assimilated by the tissues before reaching the systemic circulation. The excrementitious compounds formed by tissue waste are absorbed by the blood-vessels, and these vessels leading into other organs capable of extracting all deleterious matter from the blood, the circulating fluid leaves them freed from waste and noxious compounds before it again permeates the different parts of the system. In further organising the absorbed nutritious compounds, the liver takes an important part, as also do the glands of the lacteals and lymphatics and the lungs as well. The principal agents in removing superfluous matter from the blood are the kidneys, lungs, liver, and skin. The kidneys secrete from the blood the excess of moisture, the waste albuminous substances, and nearly all the mineral salts in solution, all of which are conveyed from them to the bladder, and thence voided as urine. In the lungs the venous blood gets exposed to the oxygen there inhaled in the common air, and such blood greedily absorbs the oxygen. Carbon and hydrogen combine with it, and are exhaled with the expired breath as carbonic acid and watery vapour. The oxygen combines with the blood's colouring matter as well, and is readily yielded up by the latter to the tissues, in order that there may be effected the oxidisation and chemical change of their component substances. Besides its functions in the process of digestion and of organising compounds absorbed by the blood, the liver has to discharge the supplementary one as well of purifying the blood from the presence of certain bodies, which are for the most part compounds of carbon and hydrogen. The skin excretes gases and moisture—carbonic acid and watery vapour for the most part; but also minute quantities of compounds similar to those in urine, and this in the acts of sensible and insensible perspiration alike. Such compounds as those last mentioned are also to some extent exhaled from the lungs.

The principal bodily excretions are urine and the faeces, which, committed to the soil, are still of value for the purposes of plant life. Urine, as we have seen, chiefly contains disorganised albuminous compounds and inorganic salts. Summarily, the different compounds of faeces may be stated to be those which have been taken into the body with the food and carried through it, without having been assimilated. Unless there is consumption of food rich in albuminous matter, or the latter is present in the former in an indigestible state, the faeces contain but a small proportion of nitrogen. The principal constituents are unassimilated inorganic salts.

To epitomise, alimentary substances are introduced into the stomach, there to be broken up and dissolved, and passed thence into the intestines, where they are still more completely fitted for assimilation by the action of the absorbents. The saliva changes insoluble starchy matters into soluble saccharine compounds, until this process is arrested by the gastric fluid ; but the fluids from the liver and pancreas renew the arrested operation when such matters have been passed into the intestines. The albuminous compounds are in considerable part dissolved by the gastric fluids; those passing from the stomach undissolved are further acted upon by the intestinal fluids. The oleaginous compounds are broken up, but are otherwise unacted upon by the gastric fluids. When subjected to the action of the bile and pancreatic fluid, they are broken up into minute globules covered by albuminous matter. The more solid and fibrous parts of the food but little altered by these agencies are passed on to the rectum, and thence defecated together with the remaining unab-sorbed materials. The blood-vessels ramifying through the inner coats of the stomach at once begin to absorb all soluble compounds—saccharine, albuminous, and inorganic—which can penetrate the enclosing membranes of the vessels. These absorbed compounds are passed together with the venous blood through the several elaborating and secreting organs, there to be prepared for assimilation in the tissues. The compounds resulting from muscular action and the breaking up of tissue substance are in part absorbed by the lymphatics, but principally by the blood-vessels. The compounds absorbed by the lymphatics are supposed to be such as are not entirely excrementitious, but still further capable of organisation and assimilation. The blood is purified from all used up or unnecessary compounds during their passage through the various excretory organs.

Albuminous compounds pass by the several names of flesh formers, or of proteine, plastic, and azotised, i.e., compounds containing nitro gen. Before absorption they are converted into a compound named albuminose, which in the blood soon assumes the forms of albumen and fibrin; the blood then circulating in the capillaries effuses through their enclosing cellular membranes into the tissues its fluid and gaseous contents; whereupon the albuminous compounds go to build up and replace such bodies as the fibrin and albumen contained in the muscular fibre of flesh, the casein in milk, the gelatin in the bones, ligaments, horns, hoofs, hair, wool, &c, and chondrin in cartilage or gristle. The oleaginous compounds, or fat formers, supply material for storing up fat in the system. The adipose or fat cells are congregated in nearly every part of the system. In the case of animals fattened beyond natural requirements these cells are deposited in increased quantity in all the soft tissues, thus increasing the size and plumpness of the different parts of the frame; but at the same time their presence greatly interferes with the continuance of muscular vigour. They are also termed heat producers, as by the oxidation of their carbon and hydrogen in the lungs and tissues they serve to maintain the requisite temperature of the blood. The amylaceous and saccharine bodies are termed the respiratory or heat-producing compounds. Their carbon and hydrogen are oxidised in the lungs and other parts, and carbonic acid and water produced thereby, as in the case of the last-mentioned compounds. It is supposed that their excess in the blood is capable of conversion through exchange of atoms into fatty material. As before mentioned, the production of heat ensues upon all movements whatever of animal bodies. The oleaginous and amylaceous compounds alike are incapable of supplying flesh-forming materials, the reason being that they do not contain nitrogen.

There is a peculiar modification of stomach represented amongst the ruminant animals of the farm, those, namely, which are commonly said to "chew the cud." The stomach in their case is divided into four different compartments, viz., 1st (in order form the gullet), the rumen, or "paunch;" 2d, the reticulum, or honeycombed bag; 3d the omasum, or "manyplies;" and 4th, the abomasum, or stomach proper. The gullet or oesophagus is continued to the third stomach; but in passing over the openings into the rumen and reticulum, it is slit in such a manner that a small amount of pressure opens its folds, and affords a passage into those two divisions. In the act of feeding, ruminant animals, it will be seen, swallow their natural food before it is thoroughly masticated. This, in being swallowed, deposits its bulkier and more imperfectly chewed portions into the rumen and reticulum, through the pressure of such portions upon the two folded openings into the same respectively, the larger pieces naturally entering the rumen. And there it remains, and is acted upon by the saliva swallowed along with it, until the animal ceases browsing. Meanwhile the reticulum has been receiving the supply of the rumen. When the animal, in the next place, commences to ruminate, the contents of the reticulum are ejected through the folds of its communicating aperture into the gullet in the form of small pellets, and by an inverted muscular action of the gullet these are conveyed to the mouth, where they undergo a thorough leisurely mastication. Reduced by this process to a soft pulpy mass, its second passage down the gullet-is unaccompanied with the requisite amount of pressure to open the passage into its former receptacles, and it passes easily and smoothly to the omasum. In like manner almost all fluid, softish or gruelly food, passes directly to it in the first instance. It may almost be said that the gullet is continued through the omasum into the fourth stomach. The inner coats of the omasum are arranged as a great number of closely-placed folds, and any substance imperfectly reduced, or triturated, so to speak, passing along the continuation of the gullet, becomes perfectly reduced, having to pass between these folds or "manyplies" before entering the abomasum. Here finally, where is secreted the gastric juice, does digestion proper commence. The abomasum leads directly into the duodenum.

Here, inasmuch as poultry form in many instances an important branch of the live-stock of the farm, it may be as well briefly to advert to the characteristic modification of the digestive portion of their alimentary canal. Midway between mouth and stomach is situated the ingluvies or crop, a pouch formed by folds or a species of dilatation of the gullet; and here the grains and similar hard food swallowed entire are stored up in the first instance. The food is gradually passed to the gizzard, where it is crushed and ground up between the muscular sides of this organ, which are lined with horny membrane. Its peculiar action is greatly aided by the presence of the sand and minute stones which the fowl instinctively swallows. The "proventriculis," or stomach proper, has to be passed through, however, before the food enters the gizzard. In the former is secreted the gastric juice, whence it is that the food is subjected to its influence before being triturated by the gizzard's action. The gizzard opens into the duodenum.

With regard to the reproductive process in animals, the principal organs for producing and developing the embryo in the female are the ovaries, in which are developed germ cells or ova, and the uterus or womb, where the ova are impregnated by the male animal, and where the ova are afterwards developed and sustained by the blood of the mother until they are ripe for parturition. There are two ovaries, one on either side, and they are situated in the region of the loins. They communicate with the uterus by the Fallopian tubes, which are certain very narrow channels. The ova, produced at periodical intervals, pass through these tubes to the uterus, and their presence in that organ is made evident by the phenomenon of "heat" or "rut" in the female. If sexual intercourse, and the impregnation of one or more ova, do not supervene, the ova are soon discharged from the body. In the opposite event the ovum is retained in the womb, and there sustained by union with the maternal blood circulation through the successive stages of embryonic growth, up to the stage when it can maintain its separate existence as a fully developed animal of the species ; whereupon the union is broken and the young animal expelled from the mother's body by a wonderful muscular action of the uterus. Until able to provide for itself, the young animal is fed with the mother's milk, elaborated from the blood by her mammary glands. The testes in the male animal are the corresponding organs to the ovaries; they secrete the seminal fluid, containing sperm cells,—spermatozoids,—which being discharged during the sexual act, and coming into contact with the ova, serves to fertilise the latter. By castration, or the removal of the testes, the male animal is rendered incapable of performing his share of the reproductive process, but at the same time he becomes more docile in disposition, and he is more easily and economically fattened than he could have been before the deprivation. The female when deprived of the ovaries assumes the like characteristics. In the case of fowls the ova, whether fertilised or not, are expelled from the body in a complete state in the form of eggs. They contain within the shell a thick layer of nutritious albuminous matter,—the "white," —which affords nourishment, when impregnation has been effected, to the growing embryo during the period of incubation. The physiological functions of correlation hardly fall within the scope of such a work as the present.

Chapter VI.—Of Meteorology.

The atmosphere, or aerial rind enclosing our globe, is composed of a mixture of oxygen and nitrogen, and a small proportion therein of one or two other gases. Purified air consists of 4 volumes or 77 parts by weight of nitrogen, and 1 volume or 23 parts by weight of oxygen. But common air also contains a considerable quantity of watery vapour, and carbonic acid as well, the latter in the proportion of about 4 volumes to 10,000 volumes of air; and 1 part of ammonia to 1 million parts of air. Nitric acid is also present, but in minuter quantity than ammonia. The height to which it continues above sea-level is uncertain, and variously estimated at from 45 miles upwards. At the sea-level its average pressure upon all objects is at the rate of 15 lbs. on every square inch, and it can support a column of mercury 30 inches high in a tube in vacuo, whose only open end enters the mercury contained in an open vessel. Such an arrangement constitutes the invaluable instrument, the barometer, the measurer of atmospheric pressure, and as such, an indefinite multiplier of science. Aerial density gradually diminishes as we ascend above the sea-level, and with it aerial pressure as well. Heat expands air, which decreasing in density, ascends; its vacant place being occupied by a fresh supply possessed of the normal coldness and density. Hence the origin of the winds and the constant atmospheric movements round the earth. The constant ascent in this manner of the body of air superincumbent upon the tracts of ocean, having a breadth of belt extending to one or two degrees on either side the equator, and the supply of colder air to fill up the vacuum, combine to effect the beneficial phenomenon of the steady trade winds. And their prevailing direction is consequent upon a supplementary fact, viz the greater speed of terrestrial revolution at the equator, arising from the earth's increased diameter at that part; for this swifter easterly motion than at other parts of the earth's surface makes the trade winds fall behind, so to speak, and to seem blowing from the north-east and south-east. To the irregular occurrence of partial aerial rarefaction is due the phenomena of monsoons and all winds great and small. From water, moisture evaporates at all temperatures, even when it is in the form of ice or snow and the air has the property of being able to hold a large quantity of such aqueous vapour in suspension. The higher the temperature of the atmosphere, the larger the proportion of aqueous vapour it can absorb; therefore it possesses various degrees of saturation, i.e., points beyond which it can hold no more in suspense. As air becomes cooler, so does its power of saturation also become lowered; whereupon all the watery vapour in excess is condensed, and falls as rain, or is deposited as dew. Dew is produced by the rapid radiation of heat from the warm surface-ground and herbage after sunset These becoming cooler than the immediately surrounding air, the latter in turn parts with its heat to them by radiation, whereby it has its saturation point lowered, and the excess of vapour becomes deposited as dew. And so with fogs and mists; they result from the radiation of heat from land and water, taking with it aqueous vapour, which becomes visible upon encountering cooler air. Similarly rain is produced when heated volumes of air are deprived of their heat, through the fall of condensed vapour, which assumes, according to the temperature it encounters, the form of ram, hail, or snow. The following table gives the weight in grains of a cubic foot of vapour at successive ascents of 10° from 0° to 90° Fahrenheit, clearly demonstrating the increase of the saturation point with the rise of temperature:-

"When by any cause the temperature of the air is reduced, its particles (molecules), approach nearer each other, and so do those of the vapours held suspended in the air; and as steam becomes visible when mixed with atmospheric air, so vapour becomes visible when it suffers condensation by a reduction of temperature, and then becomes clouds. These differ much in altitude and size." In this way we can visibly perceive the contained watery vapour in our lung exhalations during frosty weather, as also at such times as the atmosphere is already saturated with moisture.

On this natural provision of the aerial absorption of moisture depends the entire system of circulation of water from earth to sea, and vice versa. From the immense tracts of the tropical seas, and those of less heated zones, enormous volumes of water are being continually uplifted into the thirsty air. And this saturated air, becoming impelled in every direction by all the winds that blow, meets with cold elevations and land surfaces, or colder currents; whereby, losing its excess of temperature by means of radiation, its corresponding excess of moisture is condensed, and descends as rain to promote vegetable life, to fill our springs, rivers, and lakes, and take a leading part in effecting the physical and chemical changes which are constantly occurring, and altering the general contour of the world.

The frequency rather than the amount of rainfall, indicates the atmospheric humidity of any district. Generally speaking, the number of days in a year on which there falls rain, increases as we recede from the equator to the temperate zones ; and the amount of rainfall decreases with distance from the equator with increased elevation above sea-level, and with distance from the sea:—

The rainfall of the tropics is estimated at 95, and of the temperate zones at 34 inches annually. In some parts of the West Indies, as much as 600 inches have fallen in one year.

In the comparatively small area of Great Britain there is yet large diversity of the amount of rainfall, humidity, and temperature of the atmosphere. This, besides being due to local physical causes, arises from others prevailing over a large portion of the earth.

In some districts sheltered by higher ground from unfavourable winds, the temperature is much higher than it is in less favoured districts, and from the condensing action of the hills the humidity is also greater. The prevailing westerly winds come moisture-laden from the Atlantic into contact with the colder surface of the western parts of our islands; they become lowered in temperature, and consequently part with much of their moisture at the place of contact, in the form of mists and rain; and thus they keep these parts at once warmer and more humid than the eastern districts of the kingdom. Such influences have, by necessity, a considerable bearing upon the question as to the preferable system of agriculture for adoption in these districts respectively. For whilst the possession of an atmosphere humid to excess, with its attendant want of frequent sunshine, renders certain districts incapable of properly maturing our more valuable cereal crops, they are at the same time better fitted for the cultivation of the important green crops, and thereby better calculated for the successful practice of the several systems of stock-farming than other, in some respects, more highly favoured counties.

The following remarks of the English Registrar-General are of interest in this connection. He says:—"Rain fell in London to the amount of 43 inches, which is equivalent to 4300 tons of rain per acre. The rainfall during last week" (February 1865) "varied from 30 tons per acre in Edinburgh, to 215 tons per acre in Glasgow. An English acre consists of 6,272,640 square inches, and an inch deep of rain on an acre yields 6,272,640 cubic inches of water, which at 277,274 cubic inches to the gallon makes 22,622.5 gallons; and as a gallon of distilled water weighs 10 lbs., the rainfall on an acre is 226,225 lbs. avoirdupois; but 2240 lbs. are a ton, and consequently an inch deep of rain weighs 100.993 tons, or nearly 101 tons per acre. For every 100th of an inch, a ton of water falls per acre. If any agriculturist were to try the experiment of distributing artificially that which nature so bountifully supplies, he would soon feel inclined to rest and be thankful."

Numerous experiments have satisfactorily demonstrated that the amount of water exhaled by the plants on an acre of ground is in excess of its amount of rainfall. As therefore nearly 2-5ths of the total rainfall are carried away by the drainage, it will be better judged to what an extent takes place an almost insensible circulation of water from earth to atmosphere and reversely.

The atmospheric temperature decreases as we approach the higher latitudes from the equator, and also with increased elevation above the sea-level. For every 300 feet of ascent above the sea-level the mean or average temperature decreases 1°. But with increasing distance from the equator there is no uniform gradient of decrease, owing to the unequal distribution of sea and land and other causes producing a variation of temperature in parts of the world included in the same degrees of latitude. The lines which cover tracks of the world having the same mean temperature are called "isothermal lines." The atmospheric temperature is measured and indicated by the thermometer, which contains mercury or fluid in a closed glass tube, from which the atmospheric air has been extracted. Its contents expand and contract under the influence of heat and cold; and the amount of these respectively is indicated by the standard scale of degrees according to which the instrument is graduated. They are also constructed with an arrangement for registering the maximum amount of cold which has been reached during any fixed period. The hygrometer indicates the amount of moisture contained in the atmosphere immediately surrounding it; whilst the hygro-scope again merely indicates its presence. Anemometers are instruments used for measuring the amount of the wind's force and velocity. As exhibiting the influence of temperature upon the distribution of plant life in the earth, we find the face of the globe in physical atlases, from the equator to the pole, roughly divided into eight isothermal zones, with characteristic plants, as follows:—

The same applies to the vertical isothermal lines, i.e., those indicative of similarity of temperature in distance above sea-level. We can see the effects of temperature on the choice of cultivated plants exemplified within the limited area of our own country, in the presence and absence of certain field crops, as we travel from the southern to the northern extremity of our island. The important bearing which the science of meteorology brings more immediately upon agricultural practice has until recently been almost entirely overlooked; but now its principles, and their connection with the flourishing of farm crops and the welfare of live-stock, are more entirely appreciated. And there is all the more reason for this, from the peculiar situation of our kingdom subjecting it to numerous, extreme, and sudden changes of weather. The farmer can now, at the same time, more successfully combat with these, through the agency of the widely-disseminated weather-charts and forecasts, the fruits of the system so admirably organised by the Government department of the Board of Trade.

Chapter VII.

Of the Leading Scientific Principles of the Art of Agriculture.

The perusal of the foregoing chapters will have prepared the student for tracing the relation of the various physical sciences therein successively treated of, to the leading principles of agriculture, as they will next be practically adverted to in the remaining portion of this manual.

The classification and the chemical and physical characteristics of soils will fall to be considered by way of preliminary matter, seeing that the soil is the primary essential requisite for affording the plant a foundation on which to begin the formation of its structure, and, at the same time, in connection with the atmosphere, supplies all the elements necessary for the plant's growth. And before doing so a brief recapitulation is expedient of the plant's mode of absorbing its organic and inorganic constituents. The plant is but little dependent on the soil as a source of carbonic acid supply, as it is the carbon of the atmosphere which it is constantly absorbing and assimilating. Still, a considerable quantity of the atmospheric carbon is being carried into the soil when the former is dissolved by rain water. And when it is there freed by chemical action a proportion of it is directly absorbed by roots. Water necessary to the plant, yielding oxygen and hydrogen, the roots can absorb; and likewise, in some measure, the leaves, when the air is damp. Nitrogen, although existing free to so large an extent in the atmosphere, is not available for plant life in equal measure with these other three inorganic elements. It is only to a limited extent that plants can absorb the nitrogen of the atmosphere; and then it is the -ammonia and nitric acid it contains and only from the ground as a source, into which, both being soluble in water, they are carried by the rain. On this point Liebig says:—"As regards the quantity of ammonia thus brought down by the rain, ... as 1132 cubic feet of air, saturated with aqueous vapour, at 59° Fahrenheit, should yield 1 lb. of rain water, if the pound contain only l-4th of a grain of ammonia, a piece of ground of 26,910 square feet—43,560 square feet being an acre—must receive annually upwards of 80 lbs. of ammonia, or 65 lbs. of nitrogen; which is much more nitrogen than is contained in the form of vegetable albumen and gluten in 2650 lbs. of wood, 2500 lbs. of hay, or 200 cwt. of beetroot, which are the yearly produce of such a piece of ground ; but it is less than the straw, roots, and grain of corn which might grow on the same surface would contain." Other chemists, however, calculate the amount of nitrogen carried by rain to the soil at a much lower figure than the Baron does. Humus, or the organic matter of soils, absorbs ammonia from the atmosphere, and when existing free in the soil; in like manner does clay. Nitric acid and ammonia are also produced in the soil by the decay of animal and vegetable substances containing nitrogen. The former combines with bases, such as potash, soda, or lime, to form nitrates; and these and the ammonia become absorbed by the clay or humus. It is understood that plants absorb the liberated ammonia in a direct manner, and nitric acid in the same way; although in regard to the latter the question is more undecided. These, accordingly, are the natural sources whence plant life obtains the necessary organic elements of carbon, hydrogen, oxygen, and nitrogen. The inorganic compounds, whence are derived the inorganic elements necessary for the upbuilding of plant structure, exist in the soil in, as we have seen, an almost insoluble condition. But rain water holding carbonic acid in solution has, we know, its soluble power over such compounds in the soil vastly increased. But even with this, and the additional fact of so large a quantity of it permeating the soil and plant structure (experiment has shown that for every grain of inorganic matter assimilated by a plant, 2000 grains of water have passed through the latter), still plant life could not derive inorganic substance in sufficient quantity, without the additional agency of the power stated to be inherent in roots, of contributing by chemical or other means to the solubility of the compounds of this class with which they come into contact in the soil. By heat and light these several absorbed compounds, when exposed in the leaf or elsewhere, are broken up, and their atoms and molecules rearranged, to form the proximate and other compounds found in plants.
The several constituents of plant life "all form," says Johnston, "more or less constantly and abundantly a portion of the fixed and solid matter of the plant taken as a whole. They may not be found in any one part of the plant when separated carefully from the rest; but in the solid parts of the plant, taken as a whole, they are all and always to be met with. When thus deposited they become, for the most part, dormant, as it were; and for the time cease to perform an active chemical function in the general growth; though, as vessels or cells, they may still perform a mechanical function. They undergo various chemical changes in the interior, chiefly while circulating or contained in the sap, by which changes they are prepared and fitted for entering, when and where it is necessary, into the composition of the solid or fixed parts of the plants. Thus the starch of the seed is changed into the soluble dextrin and sugar of the young plant, and then again into the insoluble cellular fibre of the stem or wood as the plant grows ; and finally, into the insoluble starch of the grain as its seed fills and ripens. They each exercise a chemical action more or less distinct, decided, and intelligible upon the other elementary bodies, and the compounds of them, which they meet with in the sap of the plant. In regard to some substances, such as potash and soda, the sulphuric and phosphoric acids, this last function appears to be especially important.; These substances influence all the chemical changes which go on in the interior of the plant, and which modify or cause its growth.

The same is true of the nitrogen which the plant contains. This elementary body, in the form of albumen, or some other of the numerous protein compounds which occur in the sap, presides over, or takes part in, almost every important transformation which the organic matter of the living vegetable undergoes. Thus it is always abundantly present when the starch of the seed or of the tuber is dissolved and sent up to feed the young shoot; and again, when the soluble substances of the sap are converted into the starch of the grain of the tuber, or of the body or pith of the tree, one or other of the protein combinations is always found to be present on the spot where the chemical change or transformation is going on. Besides these general functions, the several substances found in plants exercise also special functions in reference to vegetable life and growth. Thus, nitrogen is most abundant in the sap of young plants, takes part in most of the changes of organic compounds which go on in the sap, and fixes itself, as the plant approaches maturity, in greatest abundance in the seeds and in the green leaves. Nitrogenous manure alone produces negative results. Potash and soda circulate in the sap, influence chemical changes very much, and reside or fix themselves most abundantly in green and fleshy leaves, and in bulbous roots. Sulphuric acid is very influential in all chemical changes, is found in most cases in those parts of the plant in which soda and potash abound, and deposits a portion of its sulphur wherever the compounds of nitrogen form a notable part of the substance of the plant. Phosphoric acid exercises also much influence over the chemical changes of the sap, and finally fixes itself in greatest abundance in the seeds and other reproductive parts of the plant. Soluble phosphates, from whatever source derived, produce no difference, whether as dissolved guano, coprolites, or bone ash. Lime is very important to healthy vegetable growth, as practical experience has long testified. Among other duties, it appears to accompany the phosphoric acid in the sap of plants, and to deposit itself in combination with organic acids in the leaves and bark, and with phosphoric acid in some seeds and roots. Magnesia appears also to attach itself very much to phosphoric acid in the sap, and fixes itself in combination with the acid principally in the seed. Chlorine—the chemical function of this substance in the sap is less understood even than that of the other substances above-mentioned. It exists chiefly in combination with soda, and is much more abundantly present in some plants, and in some parts of plants, than in others. Though, as I have said, its immediate chemical function in the plant is not understood, it forms a most important constituent of the plant, in so far as the after uses of vegetables in the feeding of animals are concerned. Silica exists in the sap in a soluble form, and deposits itself chiefly in the exterior portions of the stems and leaves of plants. It is supposed there to serve as a defence to the plant against external injury, and to give strength to the stem in the case of the grasses and corn-yielding plants; but what chemical functions it performs, if any, in directly promoting vegetable growth, we can scarcely as yet even venture to guess."

The following analysis of a good arable light sandy loam by Anderson will give an idea of the manner in which the several elements are combined in the soil, although the several salts are broken up into their component acids and bases:—

Soils.

From the difficulties which attend the obtaining of complete analyses of soils, no large amount of attention has hitherto been devoted to this branch of agricultural chemistry, except in instances where the object has been to determine the quality of some of the more important and indispensable constituents, such as lime. It will easily be granted, what a variety the analyses of different soils must present. The width of variation must he obvious, which exists between the composition of the soil of a chalky district and of soil taken from a reclaimed peatmoss. And again, whilst the analyses of two soils may show an almost identical composition, their measure of fertility may still be very unequal, owing probably to the soluble nature of the components of the one, and the different conditions of combination, and lessened degree of solubility prevailing with the constituents of the other.

In connection with the analysis last above given, the following table, extracted from Stephens's "Book of the Farm," give the amount of ash or inorganic material taken from the soil by some of our cultivated plants—the quantity being for every 100 lbs. of each plant:—

From these tables we perceive what a small percentage of the weight of plants is contributed by the inorganic materials of the soil.

Clay and sand are the two substances which determine the texture of the soil; and to the variety of their admixture, in regard to their respective proportions, are due the different classes of soils. The following classification of soils, as proposed by Johnston, may be selected as being the simplest, and that one, at the same time, by whose standard the classification of any particular soil may most easily be determined.

The purest clay, such as pipe-clay, found naturally, consists of silica, alumina, and a small quantity of oxide of iron, in chemical combination. No sand can be extracted from it. Tile clay, the strongest of soils, consists of pure clay, mixed with from 5 to 15 per cent. of siliceous sand; this can be separated from the clay by boiling, or otherwise thoroughly incorporating the clay with water, and then allowing the mixture to settle. The sand settles first, and the liquid can be poured off just as the finely divided clay begins to be precipitated at the bottom of the vessel.

A clay loam permits of from 15 to 30 per cent. of fine sand to be separated from it in this manner.
A loam, from 30 to 60 per cent.
A sandy loam, from 60 to 90 per cent.
A sandy soil contains no more than 10 per cent. of clay.
A marly soil is one on which the proportion of lime contained ranges from 5 to 20 per cent.
A calcareous soil is one where the lime exceeds 20 per cent.
Vegetable moulds have their range from the garden mould, containing from 5 to 10 to the peaty soil in which the organic matter may amount to 60 or 70 per cent.

The last three classes of soils are also clayey, loamy, or sandy, according to the description of the predominant element of the admixture. This organic matter or humus springs, as we have seen, from vegetable decay, When abundant, as in the case of peaty soils, it is inactive, and inorganic matter is deficient in quantity. But after drainage, and in regular cultivation, humus rapidly decays, and gets used up till the subsoil is reached and incorporated with the remaining humus, when there is found a more normal soil.

The amount of humus persistent in our cultivated soils is rarely less than 5 per cent. Chemically, it is a mixture of several acids, varied according to its stages of decay, all composed of carbon, hydrogen, and oxygen. It is not considered to be a direct source of food to the plant, but it is of great importance as a chemical agent for effecting changes in the soil. As previously mentioned, it absorbs ammonia from the atmosphere, and when free in the soil, and also soluble alkaline compounds, thereby preventing their being washed out of the soil; and at the same time so retaining them, that they can easily be liberated and absorbed by the plant roots. It likewise absorbs oxygen from the atmosphere, and freeing it in the soil, maintains a constant chemical action amongst the several constituents. Clay possesses similar absorbent properties, and its presence is therefore of considerable value, when not so intrusive as to impede the exercise of proper cultivation.

With regard to the matters carried away in solution by that portion of the rainfall which is drained out of the soil, Prof. Anderson, in commenting on the analyses of different drainage water from various soils—the rainfall estimated at 25 inches—by Way and Krocker, says:—"It appears that about 2/5 of all the rain which falls escapes through the drains, and the rest is got rid of by evaporation. An inch of rain falling on an imperial acre, weighs rather more than a hundred tons; hence, in the course of a year, there must pass off by the drains about 1000 tons of drainage water, carrying with it, out of the reach of the plants, such substances as it has dissolved, and 1500 tons must remain to give to the plant all that it holds in solution." (It has been already stated, however, that the amount of moisture inhaled by the plants covering an acre of ground alone exceeds the rainfall on such an area.) These 1500 tons of water must, if they have the same composition as that which escapes, contain only 2½ lbs. of potash and less than 1 lb, of ammonia. It may be alleged that the water which remains, lying longer in contact with the soil, may contain a large quantity of matter in solution, but even admitting this to be the case, it cannot for a moment be supposed that they can ever amount to more than a very small fraction of what is required for a single crop. It may, therefore, be stated with certainty that solubility in water is not essential to the absorption of substances by the plant, which must possess the power of itself directly attacking, acting chemically on, and dissolving them. The mode in which it does this is entirely unknown, but it, in all probability, depends upon very feeble chemical action, and hence the importance of having the soil constituents, not in solution, but in such a state that they may be readily made soluble by the plants," viz., with the particles in a finely divided state. The nitrates being the most soluble salts are washed out most abundantly.

We speak of soils as being stiff, tenacious and heavy, when they are difficult to cultivate by means of the ordinary farm power; sharp and free when they are of a gritty texture, and easily pulverised; deaf, when of a spongy, inactive texture, as when the soil adheres to the iron of the plough and other implements; deep, when they can be deeply furrowed and stirred without the subsoil being reached; thin, in the opposite case; retentive, when they retain the surface water, and admit only of its slow percolation downwards; and porous when the reverse takes place. Such other terms are applied, as rich, poor, hungry, grateful, kindly, and so on, according to the degree of natural fertility in soils, the readiness with which they absorb and retain manurial matter added to them; or, on the other hand, with which they part with it unused, or their possession, or want of other such like obvious properties.

Black soils are to be seen in peaty, white soils in chalky districts. Red soils are frequent, and for the most part they are very fertile. But the prevalent tint is a brownish one. Black, dark-coloured soils reflect the solar rays less, and consequently absorb more of their heat than do the whitish, light-coloured sorts ; but from their property of radiation, they part with heat more quickly than do the latter. Soils, exposed to the sun's hottest rays at right angles, absorb more heat than if otherwise situated. Clay soils, and such as have an excess of humus, absorb more moisture and keep it longer than do sandy soils, and such as contain a less proportion of organic matter.

Drainage.—To the end that cultivated plants may flourish, it is absolutely necessary that the soil be relieved from the presence of stagnant water; for the presence of such water, besides continually lowering the temperature of the soil, by the constant demands it makes upon the soil's heat in the act of evaporation, also precludes the possibility of air circulation through the soil's component particles: The first step, accordingly, in good husbandry, when the soil is not naturally dryish, is its artificial drainage ; which process having been effected, and the rain water now percolating through the soil into the drains, and only so much of it as is retained in the soil by capillary attraction becoming evaporable, the soil being thereby deprived of less heat, has its temperature raised considerably, promotes the earlier germination of seeds, and brings all the crops grown upon it to a speedier maturity. Land is also thus rendered capable of being worked at times and seasons in which it was formerly unworkable, and always with a less expenditure of labour. The common ways of constructing the underground ducts of drainage works in agriculture are sufficiently familiar. Clay pipes of varying shape and bore, and laid continuously in parallel rows, are usually employed, though in certain districts recourse is had to flat stones, so arranged as to form a channel with triangular-shaped bore. The surplus water then percolates the soil, and meeting the drains, leaks or soaks through the joints imperfectly fitting of the clay or stone conduits, and by gravitation it is carried through these to some clear outlet.

The Rotation of Crops.

In like manner, as the strength of any mechanical chain is regulated by its weakest link, so may the fertility of any given soil be said to depend (other conditions being favourable) on that one essential element or compound which is present in it in the least quantity of all. To the recognition of this, and the additional ascertained fact, that some plants require a greater amount of particular elements or compounds than others do, is due the custom, in agricultural practice, of observing a "rotation" or varied succession of crops, whereby it is possible to obtain permanently a maintenance of the proper balance of the soil's constituents. The annexed table, composed by Baron Liebig, in which the whole inorganic materials assimilated by plants are included under the three heads of salts of potash and soda, of lime and magnesia, and of silica, bears out the fact:—

Until quite recently, the general opinion was entertained that by the continuous growing of one particular species of crop on the same piece of ground, and that even when the appropriate manures were supplied to it, both quantity and quality of the returns gradually diminished and deteriorated, until at length its cultivation proved fruitless. As accounting for this, the theory was advanced of plants excreting matter from their roots, and that any accumulation of this was hurtful to plants of the same species as the excreting one. But this opinion must now be surrendered; and where failures occurred in cultivation after such a sort, they were due, doubtless, to mistaken ideas as to the requisite manures, and the neglect of adopting means for the check of fungoid and insect ravages. Ample proof is now afforded by results in the case of grain crops, that the same species of crop may be continuously raised on the same plot of ground with profit, provided suitable manures are applied, freedom from weeds secured, and the ravages of insects and fungi averted. But hitherto this admission has had but little effect in altering the customary and fixed rotations of cropping peculiar to different districts and estates. No doubt, so long as the great majority of soils are subjected to the present mixed method of husbandry, which must of necessity accompany the rearing and feeding of live-stock, rotation of cropping must continue as an institution, providing as it does for the requisite proportions of litter and dry and green food for the various species of animals. Its different systems are determined by the nature of climate and soil, the situation and demand of the more convenient markets, and the like considerations. But previously to observing in detail some of the ordinary rotations, it will here be expedient to notice succinctly the leading characteristics of our principal cultivated plants, the soils to which they are naturally best adapted, and the elements which they demand in greatest quantity from the soil. Wheat is the most important of our cereal crops, as it possesses the proximate constituents in the proportion best suited for man's nutrition in temperate climates ; it is therefore the staple bread-corn of the northern temperate zone. Its range of cultivation is wide, extending between the tropics and the isothermal line denoting the descent of the mean annual temperature to 56°. Also, it is cultivated in a great variety of soils ; clayey loams suit it best; and its returns are more profitable from the stronger than a light class of soils. The average composition of the grain is indicated by the figures following:—

And the average of several analyses of the ash or mineral matter gives the following results:—

Barley has even a wider range of cultivation than wheat, maturing in almost every climate in the world. Unlike the wheat plant, whose roots penetrate deeply in the soil and subsoil, those of barley ramify in the looser material nearer the surface, sending few down into the subsoil, but developing increased numbers of fibrils and hairs, so that its absorbent powers are very great.

It matures much quicker than the other grain plants; a period of from seven to eight weeks between seed time and harvest often suffices. It is best suited with light free soils. The analysis of the grain is as follows:—

Oats are also cultivated throughout a wide range, but they are better suited for countries possessing a lower annual temperature, less sunshine, and a moister climate than those in which the cultivation of wheat and barley is extensively followed. In Scotland, the breadth under oats considerably exceeds that under wheat or barley. Like wheat, the oat sends its root deep into the soil and subsoil. It is cultivated in all, but more successfully on the stronger class of soils. The analysis of this grain gives:—

The Bean plant is grown with most profit on strong soils; but it is not cultivated to anything approaching the same extent as the cereals last mentioned, as it enters but little into the composition of our bread stuffs. It is chiefly used for stock-feeding purposes, and from the large proportion of albuminous compounds which it contains, it is especially valuable in the maintenance of muscle in hard working animals. This also applies to the other cultivated leguminous plants—peas, tares, and clover. The following is the analysis of beans:—


The Turnip is a plant essentially suited to deep, loamy, light, and free soils, for these easily admit of thorough pulverisation, a condition of soil necessary for the development of the bulb, and the descent of its tap root, with its numerous diverging fibrils. As can easily be understood, from the numerous cultivated varieties, and the variety of soils in which turnips are sown, great diversity appears on analysis, but the following may be taken as averages:—

* Formed by the oxidation of the carbon.

The Mangold-wurzel, unlike the turnip, succeeds well in the strongest clay soils, though it is best suited for the medium class of these. On the European continent it is extensively cultivated for the manufacture from its saccharine compounds of the common sugar of commerce. It is largely substituted for turnips in the English midlands and eastern and southern counties, and in Ireland also. The organic analysis of the mangold is very similar to that of the turnip, but showing a larger percentage of non-nitrogenous bodies; its inorganic analysis is similar as well, excepting that it shows nearly double the amount of chloride of sodium.

Potatoes are cultivated on almost every kind of soil, though they thrive best on soils of the lighter class. They form a most important item of human dietary, and are also much used in the feeding of farm stock. The figures following represent their average analysis:—

Clovers and artificial or cultivated grasses, as distinguished from those growing naturally in pastures, are grown on all soils subject to rotation, excepting, perhaps, the strongest clays. The organic analysis of some of them is—


By conversion into hay, grasses and clovers lose about three-fourths of their weight of water.

Whatever may be considered the necessity of rotations as a preserver of the due balance of the soil's constituents, they at all events afford facilities for the periodical cleansing of the ground from the weeds, which at a subsequent period of any rotation might flourish in a particular crop, the nature of which might preclude any such purification ; as in the case of grain crops, for instance, sown broadcast or too closely drilled to admit of the intervening soil being hoed. The crops in a rotation which allow of a thorough cleansing from weeds being effected are turnips and the like, mangolds, potatoes, and so on. As these several crops are drilled at a sufficient distance apart to permit the passage of horse hoes between the rows, the soil can be thoroughly kept free from weeds till the possibility of their flourishing is taken away by the growth of the crops to such a point as to effectually protect and shade the intermediate spaces from free air and light. The crops last-mentioned, together with grasses and other forage plants cultivated for the sake of their roots or leaves, pass by the name of green crops. The grain crops, on the other hand, or those cultivated for their seeds, are called white crops, com crops, or cereals.

Formerly it was a prevalent custom at stated intervals to leave portions of ground uncropped for a whole season, repeated ploughing and other workings being granted to it during the summer, in order to destroy the weeds as far as possible. This was called giving the land a bare or naked fallow. This practice is still had on strong soils, but it is gradually yielding to that of taking out of the soil some green fallowing crops, e.g., cabbage, which is well suited to strong soils. Wheat and beans in succession, with an occasional bare fallow is an example of a two shift rotation on the strong clay soils. Wheat, beans, and fallow (either a bare fallow or a green crop) is an example of a three-shift rotation. A four-shift rotation practised in Norfolk is wheat, roots, barley, and clover. Of a five-shift, we have as an example, wheat, roots, barley or oats, and grass ("seeds") for two years. The Lothians' six-course is roots, wheat or barley, seeds one year, oats, beans or potatoes, and wheat; when the land is stiff, the wheat succeeds the roots, and beans the oats; barley and potatoes respectively being substituted where the ground is of a lighter nature. The following six-course shift is observed on some of the heavy alluvial soils of Scotland—fallow, wheat, barley, seeds, oats, and wheat. Of course there are numerous different courses of rotation, in addition to the above, according to the difference of peculiarity and requirement, in the various localities adopting them.

Manures.

Calculating upon the basis of the figures of the analyses, quoted in the preceding chapter, an average crop of wheat extracts, per acre, from the soil, inorganic compounds to the following amount:—

carried away from the soil in quantity proportionate to the analysis of the plant. Cows remove more inorganic matter from the soil than fattening animals, from the fact of their milk containing a considerable amount of such materials, not again to be delivered to the soil. In like manner, young cattle, from their requiring frame-building constituents, remove more than does fattening stock.

Phosphoric acid, then, and potash, especially the former, are the most valuable of the soil's inorganic compounds, by reason of their being the scarcest among them, but at the same time requisite in considerable quantity for the health of cultivated plants. The quantity of the remaining constituents is sufficiently contained by most soils for ordinary requirements. Potash is scarcest in light soils; in the strong clay soils and sundry closely related to several of the igneous rocks, it is constantly present in the form of one of the silicates; phosphoric acid is also more abundant in the same class of soils. We saw, that of the organic elements, that one least available to plant life was nitrogen; for all which reasons it is, that ammonia or nitric acid, and phosphoric acid form the bases of all manufactured manures ; which are called nitrogenous or phosphatic, according to the nature of the basis prevailing. Before it was commenced to manufacture mixtures of the necessary constituents, they were principally derived for return to the soil from the natural sources of farm-yard manure and town sweepings and refuse. The farm-yard manure was applied to so much of the ground as it could be spread over, the remaining arable or cultivated land was bare fallowed for a season; and, indeed, a bare fallow, in certain respects, resembles a manuring, for besides affording the opportunity of thoroughly cleansing the land from weeds, the frequent ploughings and dressings it undergoes expose its whole substance to the atmospheric action, which renders such important chemical changes, and breaks up insoluble compounds, fitting them for plant consumption in the next season.

When the situation afforded facilities for the purpose, town manure and other waste were turned to account. But a demand for other manures than these sprang up with the introduction of turnip cultivation and generally improved farming. Guano was imported, recourse was had to the use of bones; and at length the way was opened up to the production of artificial manures suitable for all kinds of crops. And now the market is full of manures compounded for the specific requirements of all our cultivated varieties, and all manner of waste and all refuse, in any respects qualified to return plant-food to the soil, are well economised, with the exception of town sewage, perhaps; for the many difficulties preventing its profitable application to the soil yet remain to be overcome. When we consider the fact of our country not producing of itself sufficient food for the population, the importation of the extra quantity needed from abroad, and the immense amount of manure stuffs now applied, and when, in addition we bring to mind the truths of all chemical elements being indestructible, and all such as compose the food of man and the lower animals being voided, some as gases, indeed, but the vast proportion in the form of fluids and solids, it must be allowed, that if its soil were the recipient of all these which are now lost, the fertility of Great Britain would naturally increase at an indefinite ratio. But, on the contrary, we see a gigantic illustration of wastefulness—the excreta of the inhabitants, and the other valuable manurial substances of our great cities and towns, poured into rivers, which are converted by the process into gigantic open sewers fatal to life, rolling everything to the sea. Where a regular course of rotation is observed, the general rule is, to apply to the green crops all the farm-yard, manure with others, in quantity sufficient for all the requirements of every subsequent crop of the rotation. But the practice of supplementing this application by another of specific manures for the successive crops, is now rapidly extending, under the influence of scientific farming.

Farm-yard manure, consisting as it does of the excreta of the various animals of the farm, and the straw of the cereals and other waste matter, contains all the elements requisite for plant life. The litter of fully grown animals, fed upon rich food, with a large proportion of nitrogenous and phosphatic substances, evidently affords a more valuable manure than does that of stock fed upon a poorer dietary, or that of young growing animals. Such manure, too, made under cover, or sheltered from exposure to rainfall, must also of necessity present a better quality than when it has been exposed to the open atmosphere and the washing action of rain. The following table from Stephens shows the proportions of the ingredients of one ton of farm-yard manure:—


Guano is composed of the excreta of marine fowls and the remains of their bodies, and it is chiefly found accumulated in thick deposits on several islands off the Peruvian coast, which are never visited by rain. Their situation in a rainless zone has prevented the washing away of the valuable constituents of these strata, which are found consolidated into a dry unfermented mass. The following is the analysis of a first-class Peruvian guano:

Ammonia contained equal to 18.95.

This shows a most valuable manure, especially rich both in nitrogenous and phosphatic compounds. Phosphatic bodies predominate in many guanos, which are thence called phosphatic guanos. From the excessive demand, the supply of Peruvian guano is rapidly becoming exhausted. New sources have been made available, but their geographical position being less favourable, the sample of guano yielded is much inferior to the Peruvian.

Of the artificial manures, various are manufactured with a fixed percentage of nitrogenous and phosphatic compounds. These compounds, however, are for the most part respectively applied in separate compositions. As nitrogen food, the principal compounds bestowed upon the soil are the two salts, nitrate of soda and sulphate of ammonia. Besides these there are many available sources of nitrogen supply, including all waste organic substances. The phosphoric acid entering into the composition of artificial manures is entirely combined with lime, in the form of a salt called phosphate of lime, and its chief sources are animals' bones, coprolites, and apatite. Of these, coprolites are found as concretions in certain rock strata, and are supposed to be the fossilised faeces of gigantic animals, reptiles for the most part existing at the time of the formation of the strata in question. Apatite is a mineral phosphate of lime, and is found in large quantity in various parts of the world. The phosphate of lime as combined in these quarters consists of two molecules of phosphoric acid in chemical union with three atoms of calcium, Ca32P04—an almost insoluble salt. To overcome the insolubility sulphuric acid is added, and it alters the nature of the phosphate, rendering it soluble, by taking from it two atoms of calcium—forming with them sulphate of lime or gypsum, and replacing the calcium atoms by their equivalent of hydrogen. Thus, Ca32PO4 + 2H2SO4 = 2CaSO4+CaH42P04. This soluble salt is termed superphoshate of lime. When bones are treated in this way with sulphuric acid they are known as "dissolved bones;" and in addition to the phosphate and sulphate of lime, they also possess a considerable quantity of ammonia, resulting from the organic matter of the bone. When the gradual absorption of phosphoric acid is desired in the soil, crushed bones and bone "meal" are applied, without their having received any such dressing. The minute mechanical division of their particles permits of a prolonged action upon them by the chemical changes occurring in the soil, and an equally delayed complete yielding up of their organic matter and phosphates; the length of such delay being proportioned to the size of the triturated particles. Bone ashes, i.e., bones deprived of their organic substance, contain fewer impurities than the natural phosphates of lime, and yield the most valuable superphosphates. "A variety of substances," says Anderson, "are sold under the name of nitrophosphate, potato manure, cereal manure, &c, which are all superphosphates, differing only in the proportion of their ingredients, and in the addition of small quantities of alkaline salts, sulphate of magnesia, and other substances, but they present little difference from ordinary superphosphates in their effects." The following, according to the same authority, are analyses of various superphosphates :—

The cheapest source of potash is the mineral called kainit, containing sulphate of potash, which has now begun to be extensively supplied to turnips, potatoes, mangolds, &c. Gypsum, or sulphate of lime, is also applied occasionally to leguminous crops.

Another method for increasing the soil's fertility employed by advanced farmers, is the feeding of sheep upon rich artificial substances, whereby, whilst the primary object of fattening the animals is speedily attained, the soil is benefited by receiving their valuable excreta, becoming enriched with manurial bodies.

Other bodies, besides, are supplied to the soil, in order to promote certain physical as well as chemical results. Thus, clay is added to light sandy and peaty soils, that thereby they may receive body or staple; and, reversely, sand and peat are added to clay soils, the former—in order to render them more friable, the latter to increase their stock of organic matter. In some districts the clay of strong soils is burnt, for the consequent effect of its friableness being increased, and many of its insoluble compounds being broken up. Lime, however, is the principal of all the substances which are added for combined physical and chemical effects. Besides disintegrating the strong clay, it also breaks up the insoluble silicates and liberates the combined alkalies. Moreover, it promotes changes amongst the organic compounds, in peaty soils especially. Nor has it less importance as being a direct source of food to plants, for all of them contain more or less lime. By its application, the quality of grain is improved, and its maturity hastened; whilst again, in pasture ground, it serves to extirpate moss and plants of low organisation. All those effects of lime are more marked and more efficacious if it has been applied in the caustic state. Frequently, however, it is applied as the carbonate, in the form of chalk, marl, and shell sand; for these are often to be had cheaply and conveniently, where lime " shells " are difficult to obtain.
In connection with the above general laws, there are numerous considerations to be attended to, in regard to the application of manures, which are too complicated, and too closely associated with actual practice, to be touched upon here. They bear principally upon the proper times, quantities, and mutual proportions which are essential to their profitable use.

Hearing and Management of Stock.—Although, in our home market, the foreign agriculturists can favourably compete with us in grain production, it is otherwise with regard to the production of beef and mutton. It is true, indeed, that, in spite of the obstacles ensured to them in a ruder system of agricultural practice, and a greater dependence of necessity on mere natural agencies for the maturing of their stock, they still can rear cheaper meat. But before our markets are reached, there are the risks, difficulties, and expenses of transit to be encountered. Doubtless, the appliances of science will tend to the gradual diminution of these difficulties, as witness the importation of cooked beef and mutton of fair quality from Australia, and the sale in some of our markets at paying figures of fresh beef from America. But before the American and European countries exporting to us can produce live stock so speedily attaining a high quality as ours do, and affording such a high-class description of meat as our markets demand, there must prevail amongs them a higher practice of agriculture, involving the introduction of improved breeds of animals. And there is no reason why British farmers should not maintain their precedence in this respect. Almost the entire number they export reach us in a lean condition, and require to be fattened here, under our more advanced system. For since, within recent times, beef and mutton have become a more important branch of our agricultural produce than grain, scientific attention has been turned to the investigation of animal dietary, with the result of many natural bodies formerly overlooked, together with new artificially prepared compounds, having come into general use in the feeding of the live stock of the farm. Physiology has taught us which of the proximate feeding compounds should be the principal ingredient in the food of each class of animals. Substances, accordingly, rich in albuminous matter, should constitute the food of hard-working animals, that fibrin and albumin may be applied to their muscular wants. To such as it is desired that they should be quickly fattened, and which undergo only sufficient exercise to maintain good health, are freely given compounds known to contain much fat-forming material. To young growing animals a fair proportion of both kinds of food is offered, and such substances in addition as hold saline bodies, like phosphate of lime, which avail for the building up of the bones. Milk affords a safe criterion of the food constituents appropriate to young animals. It is the food nature provides for them, and none other can be so perfect. According to Way, the average composition of cow's milk is—

The oleaginous bodies contained in the fluid are broken up into minute globules or cells; and when new milk is allowed to settle in any suitable vessel, these rise to the surface, and form the cream. When the cream is removed, it leaves the skimmed milk almost entirely devoid of oily matter. The albuminous matter, or casein, is held in solution by the fluid, by means of some one of the alkaline bodies ; the latter becomes neutralised by the addition of certain acids, whereupon the casein coagulates, and this curd, by pressure and suitable treatment, becomes converted into cheese. The remaining fluid, or whey, contains the sugar and the inorganic salts. The natural curdling of milk takes place when lactic acid, C3H6O3, its peculiar acid, is formed; and its presence is evidenced by the fluid becoming sour in taste. Johnson says:—"The change which takes place when milk becomes sour is easily understood. Under the influence of the casein, the elements of a portion of the milk-sugar are made to assume a new arrangement, and the sour lactic acid is the results. There is no loss of matter; no new elements are called into play; nothing is absorbed from the air, or given off into it; but a simple transposition of the elements of the sugar takes place, and the new acid compound is produced. These changes appear very simple, and yet, how difficult is it to conceive by what mysterious influence the mere contact of this decaying membrane, or of the casein of the milk, can cause the elements of the sugar to break up their old connection, and to arrange themselves anew in another prescribed order, so as to form a compound endowed with properties so very different as those of lactic acid."

Lactic acid is also produced during the churning of cream, and is supposed to aid the violent mechanical agitation, in breaking the walls of the oily cells or globules, after which the butter separates in mass from the sour butter milk. In the ordinary domestic manufacture of cheese, " rennet," an acid decoction prepared from the dried stomach of a calf, is what is ordinarily added to the milk, for the purpose of coagulating or curdling the casein.

As cow milk is such an invaluable article of the human dietary, calves are often early deprived of this, their natural food, or, at all events, only partake of it after its cream has been abstracted. But suitable artificial food is substituted, rich in the various proximate constituents. But even in those cases where a fair amount of milk is afforded to them, it is sometimes usual to mix with it linseed, or some similar meal, whenever the calf can eat artificial stuffs, and nutritious green food is provided as well. Lambs and young pigs are not prematurely deprived of mother's milk; but she is fed with food calculated to enrich the qualities of her milk.

Before the introduction of turnips, owing to the want of green or juicy food for the live stock during winter, the animals had attained, as a rule, their full growth and maturity, ere they were fattened enough for slaughtering. Throughout summer and the milder months they had the range of the pasturage; and in winter they were turned into the fold-yards, more indeed for the purpose of trampling down and converting the litter into manure, than of being carefully tended, and provided with nourishing food, their dietary being almost entirely composed of hay and straw. Sheep also had to subsist entirely upon the natural pasturage; few, if any, were kept on the arable farms. The state of matters is now entirely different. A variety of green crops is cultivated; there is the choice of an immense assortment of artificial feeding stuffs, and every breed of stock has been improved to the development of the most extraordinary qualities of speedy and economical fattening. Consequently, stock is kept in every district in amazingly increased numbers, and sent to the meat market in prime condition, at a comparatively early age. Even in such counties, where, from physical and climatic obstacles, a large proportion of the land necessarily remains in its natural condition, the cultivation of the residue is wholly directed towards stock-breeding and rearing, the produce of the large number of breeding animals kept being sold off as "store" cattle and sheep for fattening in more favoured districts. In point of fact, since the increased demand for prime " butcher meat," down through all ranks of the community, has so particularly raised the price of the article, the great end of all British agriculture is becoming more and more exclusively the rearing and feeding of live stock.

The peculiarities of the digestive economy in ruminants, rendering juicy and bulky food, like our different grasses, most appropriate to their use, they cannot be reared and fattened on dry concentrated food alone, without incurring the risk of disease. During winter and the non-vegetative months our various green and root crops form admirable substitutes for grasses. Concentrated feeding stuffs added to the natural bulky food, whilst they do not impair the digestive functions, supply the absorbents with materials rich in the several proximate compounds for maintaining and multiplying the animal tissues. As we have seen by the foregoing analysis, grasses and clovers are much more nutritious than equal weights of turnips ; wherefore, stock which is being fattened on grass does not, as a rule, receive concentrated feeding stuff in addition, though under the high pressure system, the contrary practice is beginning to obtain. Animals being winter fed, however, receive, as a matter of course, artificial food in addition to the straw and turnips ; and their quickly increasing weight is the justification. Stuffs, rich in albuminous proximate compounds, are the most valuable, by reason of their affording the necessary flesh-forming material, and at the same time increasing the manurial value of the excreta; and their value reaches a maximum by the daily proportionate admixture of oleaginous and respiratory bodies. Of grains most used are ground barley, beans, and Indian corn; wheat and oats are not often given to pasturing stock, though the last is often put before store cattle. Bran, malt dust, and the refuse malt and liquids of breweries and distilleries, are also made use of. Of the many waste substances of the manufactory, which chemical knowledge has made available for stock feeding, the most important are the solid cakes or tablets, the residuum of the oil-extracting process by pressure from linseed, rape seed, cotton seed, &c. As these contain some of the oil, and all the other proximate constituents in the composition of the seed, they constitute a most invaluable concentrated feeding stuff. It ought not to be lost sight of, that however high their value, as containing such constituents may be, it must needs be regulated by their properties of easy digestion, otherwise such constituents will pass through the alimentary canal but little acted upon. Digestibility accordingly, especially in the case of fibrous substances, is greatly promoted by subjecting feeding stuffs to steaming, or such like concoction, or to fermentation.

The following table from Anderson, gives the nutritive composition of numerous feeding materials:—

It is obvious that a barely sufficient supply of food for the daily wear and tear of an animal's existence will not contribute to any increase of the animal's weight. To produce this last effect an excess of nutriment over what is requisite for daily wants, and even above the limits of the power of absorption and assimilation, must be afforded. Albuminous bodies, as we have seen, replace and increase muscular tissue, whilst the oleaginous bodies do the same for the fatty tissues. As the latter multiply, they become deposited in all parts of the otherwise dense muscular tissues of the body, increasing their bulk and juiciness, and rendering them more tender and palatable and easy of digestion as human food. The saccharine and amylaceous bodies are primarily appropriated for the respiratory processes ; but their excess, present in the blood, is also capable of conversion into fat-forming material, though in a less degree than the oleaginous constituents. For whilst 1 lb. weight of the latter can supply 1lb. of fat to the animal body, it takes 2½ lbs. of respiratory compounds to produce an equivalent result. To many it is probably an unsuspected fact, that even in lean animals, the fat contained in the whole body exceeds the quantity of albuminous substance. The following table, also derived from the last-named authority, and based upon calculations resting upon the elaborate experiments of Messrs Gilbert and Lawes, shows approximately the general composition of the entire carcass of a lean and a fat animal respectively:—

Whence it appears that for every 1lb. of albuminous matter assimilated by the system, there are likewise assimilated, in round numbers, 10 lbs. of fat and 3 lbs. of water. Theoretically, it might be assumed that a similar proportion should prevail in the food material given to fattening animals. But this is not sustained in practice. For the substances demonstrated by experience as being the most efficient for fattening our stock— for example, the various oil-cakes, grasses, leguminous plants, turnips, &c, all contain these proximate constituents in a much more equal proportion than that of 1 to 10. Any apparent anomally disappears when we call to mind that with the progress of —from a physical point of view—degeneration in the animal body, owing to the want of a natural amount of muscular exertion the albuminous bodies becomes less and less requisite to the tissues, and their absorption into the blood slower. This may either be owing to the already highly nourished and consequently denser condition of the blood retarding their absorption by the process of endosmoses, or to some obscure natural provision. At all events, the balance of the blood constituents is preserved and disease averted by reason thereof. The increased difficulty of their absorption, however, necessitates a larger quantity of the albuminous bodies being present in the food, in order that the absorbents may be enabled to the utmost to take up a sufficient modicum. All the while the fattening substances, from the ease with which they are assimilated, have their excess laid up in all parts of the system. The following table, still from the same authority, shows the amount of each class of constituents stored in the increase, for every 100 consumed in the food, by—

The last shows the greater power of assimilation of food possessed by the pig over the sheep, and its consequent property of cheaper and speedier fattening. A main object in breed improvement is the development of such a quality in stock.

Farm horses, those admirable serfs of the husbandman, are appropriately fed with dry concentrated food, rich in albuminous substances. Experience has selected oats and hay from this class, with the addition of beans in the spring and early summer months, when calls for draught power are scarce. In summer the animals enjoy a short respite, when grass is given, as being-better suited to diminished muscular expenditure, and economical at the same time.

As regards the actual details of ordinary agricultural practice and routine, these, indeed, can best be learned by experience in the field. In every county, nay, almost in every parish, they vary appreciably. But the scientific principles of agriculture are equally applicable in every country and clime, and the student may investigate them to their utmost extent in the works of Stephen's; Wilson's Farm Crops; Liebig's, Anderson's, and Johnston's writings on Chemistry applied to Agriculture; Roscoe on Chemistry; Geikie on Geology; and Balfour and Brown on Botany, with many other volumes too numerous to mention.


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