guardianship of a higher, mysterious power, called the vital force, and are compelled by this to furnish the materials for the construction of the animal or vegetable organism. The vital force is, so to speak, the architect which designs the building, whilst the chemical processes must see to the provision of the requisite materials, and their elaboration in conformity with the design. In lifeless bodies, on the contrary, this guardianship no longer exists, and the chemical processes have free and unimpeded scope for action. The chemist can evoke and imitate the action of chemical forces, but by no means that of the vital force; therefore in cases where chemical power enjoys free dominion, he will attain to positive results more easily and rapidly than in others, where the vital force, over which he can exercise no sway, comes at the same time into opposition with him.

Finally, chemistry possesses a detective function, whereby it proves useful to every man, and therefore to the farmer, since it discloses frauds and impostures, to which, as is well known, all are at present more exposed than formerly. Pure goods! Genuine goods! Solid goods! Real goods! What manufacturer or merchant does not now-a-days deem himself justified in stamping one of these commendatory appellations upon his articles of trade! And yet his real linen perhaps contains cotton; his choicest soap, water, glue, or clay; his genuine syrup, starch-sugar; his guano or bone-dust, sand, earth, limestone, &c. Against such adulterations and losses, chemistry offers the most solid and secure defence, since it possesses the power of bringing to light admixtures and adulterations, however cunningly contrived, which our eyes and other means of proof are unable to detect. Many chemical tests of this kind have been already so simplified, that any one may use them for himself without much cost or trouble.

If, after this statement of the different directions in which chemistry is capable of exercising a salutary influence upon agricultural practice, more special proof should be required of its ability to keep its promises, these might be readily supplied. Let us inquire only of English farmers; let us merely bring together the facts relating to this subject which have been published in the English agricultural journals within the last five years; or simply calculate the sums

which have been expended in that country by agriculturists themselves, for the purpose of extending and deriving profit from chemistry. We shall not only arrive at a knowledge of what an extraordinary amount has been done in England, and how extremely little in Germany, towards chemico-agricul tural objects, but also at the conviction, that there a harvest is already reaping, whilst cautious Germany is still debating the question, whether the chemical seeds sown possess germinating power or not! And the recognition of this will be fraught with blessings, if it leads to chemistry soon becoming in Germany, what from its nature and destiny it ought to be and must be,-a true home-friend to the farmer.

II. NUTRITION OF PLANTS.

An inscrutable Wisdom has implanted in the grain of seed the power of germinating in moist earth, and of growing up into a plant, which puts forth leaves, flowers, and seed, and then dies away and disappears. Germination, growth, flowering, seedbearing, and withering, are the chief stages of development through which plants have to pass. When they have advanced so far as to produce seed, that is, new bodies capable of life, they have fulfilled their appointed task, and their course again declines downward to decay. Whether this course is completed in one brief summer, or not until after centuries have elapsed, the principle is in no way altered.

1

The divine breath which calls forth these changes, the phænomena of life in the vegetable world, is in its essence entirely unknown to us. We give it a name, indeed, the name of vital force, but gain thereby no clearer understanding of its nature. Its operations are conducted in so mysterious a manner, as to render it apparently improbable that the speculations of man's inquiring spirit will ever be converted into direct knowledge upon this point, here be low. We feel, it is true, the rush of the vital current, in the joy which pervades us when in spring it bursts the buds.

and pours a flood of blossom over the earth: and again in the melancholy which seizes us when in autumn the withering of the leaves announces its departure; but whence it comes, whither it goes, and by what magic it conjures forth the miracles of the vegetable world, we have not the slightest knowledge. All our senses can detect is, what it produces, and out of what this is produced.

Two paths stand open to the inquirer, by which he may penetrate, up to a certain point, into the mysterious workshops of vegetable life:-1st. That of observation, which, by the aid of the microscope especially, has led to a very accurate knowledge of the structure of plants, and of the changes in the form of their separate parts which take place during growth. 2nd. That of chemical experiment, by which the constituent elements of plants, their means of sustenance, and certain alterations of their substance occurring during growth, have been ascertained.

From the facts brought to light by these researches, a special science, called Vegetable Physiology, or the study of the phænomena, conditions, and laws of the life of plants, has been attained, and of this science Agricultural Chemistry constitutes a principal division.

Among the problems connected with practical agriculture which this science has to solve, that relating to the nourishment of plants is of especially high importance, for it is manifest that if the farmer knew precisely what was the best food for the plants he cultivates; in what form, quantity, and at what period it must be administered, in order to obtain the greatest benefit from it, and if he were acquainted with the sources from which he could procure it cheapest, he would be able to make the most extensive and diversified profitable applications of them in his calling. Unfortunately, however, science is not so far matured as to be able to furnish certain intelligence upon all these points, but is still compelled in many cases to have recourse to mere conjectures. Nevertheless these may prove serviceable, if communicated to the farmer, not as ascertained facts, but merely as conjectures, and in such a form as to be available for the purposes of practical experiment.

That plants, like animals, must obtain nourishment in order to live and grow, no one doubts. What kind of

nourishment this is, however, it is far more difficult to make out in plants than in animals, since our senses do not enable us to perceive what vegetables take as food, or how they take it, except that they absorb water, and again exhale it: Thus much, indeed, is generally known, that soil, moisture, air, heat and light, are necessary to the growth of plants; but this amounts to very little, for very varied ingredients are contained in the soil, the water and the air, and the essential point is to ascertain which of these separate ele ments are to be regarded as articles of food to the plant, and which not. In former times men lived in the belief that the knowledge of these individual constituents was by no means so important, because vegetables possessed the power of converting one body into another; for example, lime into silica, or silica into lime, just as one or the other might be needed. This belief has been shown, however, to be erroneous. It is now known with certainty, that plants have not this power; it is further known, that they can grow vigorously and perfectly, and reach complete development, only when all the constituent elements required in their organic structure are at their disposal; hence an exact knowledge of the chemical elements of plants, of the soil, of water, and of the air, must be regarded as absolutely indispensable: as the starting-point, indeed, from which all subsequent inquiry must proceed.

The first question which requires to be answered in respect to this, is the following:

1. OF WHAT DO PLANTS CONSIST?

When the chemist wishes to investigate the composition of any body, he divides it, in the first instance, into its rougher components, and then again resolves these into their finer elements. The former are called the proximate, and the latter the ultimate constituents of bodies. If these last admit of no further separation into still simpler elements, they receive the name of elementary substances, or chemical elements*.

Numberless plants have been already examined in this way, and have been found to contain very varied proximate

*See Stöckhardt's 'Principles of Chemistry' (Bohn's Scientific Library).

constituents, which, in many cases, can be readily distinguished from each other by their appearance, taste, and other external characters*. Grapes, carrots, and many other

*The "separation of a substance into its elements," that is into its proximate and ultimate constituents, may be explained a little more fully. The separation into the proximate elements may often be almost a mechanical process, as for example in the case of any corn grain. The starch and gluten, being contained in the cavities of the substance, may be washed out of the finely-bruised grain with water; the starch will settle down from this water, being insoluble, and the gluten may be separated as a thick, viscid substance, and dried. Then the amount of the vegetable fibre may be ascertained after the starch and gluten have been washed thoroughly out, by subtracting from its weight the quantity of ash left after it has been burnt. In ascertaining the ultimate constituents, or elements, the processes are very different, for chemical decompositions are here brought into play, and the substances reduced into far simpler conditions. The proximate constituents of plants and animals are very numerous, while the ultimate constituents are the same as those forming the elements of the mineral kingdom, which amount only to about sixty-four, and not twenty of these have yet been detected in vegetables. The term element is applied to any substance which cannot be separated into any simpler substances; for example, carbon, as it is called (charcoal, &c.), is a simple substance or element, because it cannot be separated into any other kinds of body; all the metals are likewise simple elements, as are also sulphur, phosphorus, and other less familiar substances. The most important elements of plants, as stated in the text, are carbon, oxygen, hydrogen, and nitrogen; the last three are gases or airs in the separate condition, and two of them, oxygen and nitrogen, in a state of simple mixture, form the common air we breathe. Hydrogen does not occur naturally in a separate form, but is commonly diffused, in chemical combination with oxygen, in the shape of water. The two, substances, water and atmospheric air, afford good illustrations of the difference of simple mixtures and chemical combinations. Water is a liquid at common temperatures, while oxygen and hydrogen are gases; water displays none of the characters of either one or the other; it will not burn like hydrogen, or support combustion like oxygen, &c. Atmospheric air is a gas, like oxygen or nitrogen, and its weight corresponds to the proportion in which these two elements are mixed; its oxygen supports combustion, as if alone, while the nitrogen, a gas having no striking peculiarities when separate, acts merely as a diluting or weakening admixture. Yet when these two elements, oxygen and nitrogen, are united chemically, we obtain a series of substances of most active properties, nitric acid, &c., fatal to life and violently affecting other substances. If we pass a series of electric sparks through a bottle full of air, we convert the oxygen and a portion of the nitrogen into nitric acid, which has an irritating, choking vapour, corrodes metals, burns the skin, &c. If we mix hydrogen and oxygen, and pass an electric spark through them, or apply a light, the gaseous mixture (comparable in its condition to com