INCREASE OF THE GROWTH OF PLANTS BY MANURING. 31

fices for the nourishment of plants, if they but find the necessary inorganic salts dissolved in the soil.

But as a building advances more rapidly when several parts are worked upon at the same time, so the growth of a plant proceeds more quickly and luxuriantly when it can absorb nourishment from several different sources,-not only by its leaves, but at the same time also by its roots; that is to say, when the soil contains in sufficient quantity all those materials for its nourishment. Wherever this is not the case, art must assist; and this assistance is rendered by manuring, which will be discussed in the following chapter.

III. INCREASE OF THE GROWTH OF PLANTS BY MANURING.

If we give abundant and invigorating food to an animal, it becomes vigorous and fat; on scanty and slightly nutritive food it continues poor and lean. It is precisely the same with plants. If they find all the substances which they require for their nourishment and full development, in abun dant quantity and in suitable form in the soil and in the air, they will grow up more vigorously, and put forth more shoots, leaves, flowers, and fruits, than when they meet with these substances, or even only one of them, in insufficient quantity. By rich and abundant food the farmer fattens his cattle; by rich and abundant food he can also fatten his plants. this respect plants are placed in the same circumstances' as animals during stall-feeding; they are confined to one fixed. spot, and cannot quit it in order to seek in another place what may perhaps be wanting to them in this; therefore, if they are to grow luxuriantly, the farmer must take care that their food lies near enough for them to reach it by their roots.

In

In fattening animals, the farmer provides, in addition to good food, warm sheds and suitable littering, cleanliness and proper attendance, because he knows that this maintains

and increases the health and comfort of the animals, and that food acts better upon a healthy beast than upon one that is sickly. The same thing applies equally in fattening plants. If they are required to grow in greater quantity and vigour than are produced upon a field spontaneously, not only must more nutritive material be placed at their service, but at the same time a more agreeable and appropriate habitation than is offered by the raw soil alone, must be prepared. In particular, this must be sufficiently deep, loose, warm, and moist, for the roots to spread properly and the nutrient matter to be dissolved.

When, therefore, the farmer wishes to increase the natural fertility of his fields, these two courses are to be adopted, tillage of the soil, and manuring; these are the means which from time immemorial the practical agriculturist has employed, and by which he has often increased the produce of his ground tenfold, twentyfold, or in still greater proportion.

By the tillage of the soil, concerning which we shall speak hereafter, the farmer principally improves its external or physical constitution. Ploughing and harrowing diminish. the firm coherence of the mass, and at the same time render it more accessible to air and water; by which circumstance both the weathering of its mineral and the decay of its organic constituents are promoted. Deep and subsoil ploughing, trenching, &c., effect the same beneficial changes in the deeper portions, as well as an intermingling of the different kinds of earth. The latter circumstance not only places at the disposal of plants a deeper layer of soil with a greater quantity of mineral substances, but likewise ensures a more equable distribution of its moisture. By draining, the soil is not merely rendered drier, more crumbling, and warmer, but also more active and healthy;-more active, because air now penetrates, instead of water, into its interstices, producing a quicker weathering and decay;-healthier, because the access of air prevents the further generation of acids, which are notoriously disadvantageous to land-plants. The free acids already present in the soil are most rapidly neutralized by laying on marl or lime, and the activity of the soil, that is, the decomposition and solution of its organic and inorganic components, is materially promoted. At the same time an excessive tenacity of the soil is corrected, an

improvement which might also be attained, were it not in the majority of cases too expensive, by burning earths having this fault. On the other hand, soils of thin and dry character may be made more tenacious, and hence more productive, by carrying on to them loam or clay. A judicious rotation of crops may also essentially improve the physical constitution of a soil, inasmuch as leafy plants, for instance peas, clover, &c., shade the ground, and keep it moist during a whole summer, whilst deeply-rooting plants, such as rape, &c., make it loose and mellow. Finally, irrigation may in like manner contribute to the improvement of the character of the soil.

By manuring, nourishment for plants is conveyed directly into the soil. According to the preceding chapter, we have to regard as food all those bodies which are able to furnish plants with one or more of the chemical elements necessary to their growth. It must here, however, be expressly pointed out, that a plant can only grow vigorously, thrive, and attain fully to maturity, when all these chemical elements are supplied together. As the life of man ceases when any one of the conditions requisite to the continuation of his existence-for example, air (oxygen) or water-is withdrawn, as the works of a clock stand still if only a single little wheel is taken from them,-so also is the complete development of a plant checked, where even only one of its necessary elements is wanting. Hence it follows that we can only regard those manures as in a strict sense quite universal or normal, which contain all these constituents. This, moreover, explains in a very simple manner a multitude of often entirely contradictory results, in agricultural trials of one and the same manure. Lime, gypsum, bonedust, &c. act excellently on many kinds of soil; on others, not at all. If a soil contains a sufficiency of lime, then manuring with lime will be of no service; for the plants find enough of this constituent already in the ground, and therefore require no further addition of this ingredient. On the other hand, in land poor in lime or altogether without it, such a manuring may furnish extraordinary results, because it remedies an actual deficiency of this ingredient. From gypsum, plants may provide themselves with lime and sulphur; but it will only act in such soils as are destitute of

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both or at least of one of these substances. In bone-dust the principal constituents are nitrogen, lime, and phosphorus; when, therefore, it is placed upon a soil in which these elements are already present in sufficient quantity, it will have little or no effect; whereas on a soil poor in only one of these constituents, it may produce remarkable effects.

To this it must be added, that all plants which we cultivate do not require for their nourishment an equal quantity of each particular substance, especially of the mineral. Thus, for example, about the following quantities are necessary to produce 1000 lbs. of each of the following

Hence it is apparent, that very different quantities of potash, lime, &c. are necessary to produce an equal weight of each plant, and from this it obviously follows, that the action of any kind of manure will always vary according to the plants to which it is applied. Manuring with lime has perhaps no influence whatever upon rye, whilst upon peas or clover, in the same field, it exhibits a very good effect. In such a case we must suppose that the soil contains as much lime as rye requires, but not so much as suffices for a full crop of peas or clover; the first of which requires five times, and the latter ten times, as much lime as rye.

Similar differences occur, not merely in different kinds of plants, but also in the different parts of one and the same plant; which teaches us that many of the constituents of our manures act more especially upon the leaves, others upon the seeds, and others, again, upon the roots. Thus, for example, there have been found (in round numbers):

These figures can be admitted only as approximative, but they at all events show, although they do not coincide entirely with each other, that, as a general rule, the leafy parts and roots of plants chiefly require alkalies and earths (potash and lime), besides nitrogen, for their full development, and the seeds principally phosphoric acid and nitrogen. To this conclusion the leaves of the beet form a merely apparent exception, because they were examined in a green or halfmatured condition, at which stage they of course contain the materials from which the root, and, at a still later period, the blossom and seed, are to be formed. When completely mature, they contain less phosphoric acid and less nitrogen. In this state of things it will no longer seem strange, that many manures, as experience demonstrates, occasion more especially growth of stalks and leaves; and others, an abundant production of seed.

What constituents does a manure contain? This is the first and most important question the chemist has to answer, before he can furnish distinct information to the inquiries proposed by the practical agriculturist: How does the manure operate? How quickly does it act? How long does its action continue? What is its worth? &c. Manure operates only by means of the chemical substances it contains; these, therefore, must be accurately ascertained, before any exact intelligence can be afforded respecting it. Were this all, the study of manures would be in an excellent condition; for chemistry is now so far advanced, as to be able to detect and define these elements even to a thousandth part. But of what use is it to the farmer to be informed that such or such a quantity of potash, nitrogen, phosphorus, &c. is con