Manures are animal, vegetable and mineral; they directly assist the growth of plants, first, by entering into their composition; secondly, by absorbing and retaining moisture from the atmosphere ; thirdly, by absorbing the gases of the atmosphere; fourthly, by stimulating the vascular system of the plants. Manures approximately assist vegetation, first, by killing predatory vermin and weeds; secondly, by promoting the decomposition of stubborn organic remains in the soil; thirdly, by protecting incumbent plants from violent changes of temperature.

All these properties seldom if ever occur in one species of manure, but each is usually particularized by possessing one or more in a superior degree. That is the most generally applicable manure, which is composed of matters essential to the growth of plants: the chief of these are carbon, hydrogen, and oxygen; therefore all animal and vegetable substances are excellent manures. It would evidently be of great benefit, if every plant could be manured with the decaying parts of its own species; the ancients made this a particular object. We read that those vines were the most fruitful, which were manured with their own leaves and prunings, and the skins of expressed grapes. This rule might be so far followed, as that the stems of potatoes, peas, etc., could be dug respectively into the compartments where those crops are intended to be grown in the following year.

Of the less general manures which benefit plants by entering into their composition, a few words will suffice. Sulphate of lime (gypsum) is a component of clover, lucerne, turnips, etc.; hence it has been applied with benefit to these crops on such soils as did not already contain it. Hones broken small have lately become a very general manure; their utility is easily accounted for. The bones of oxen contain about fifty per cent, of gelatine, which is soluble in water, and rapidly becomes putrescent. The remainder is chiefly phosphate and carbonate of lime, salts which are components of wheat, rye, barley, oats, peas, beans, vines, cucumbers, potatoes, garlic, onions, truffles, etc.

Common salt also is employed as a manure, and is beneficial, partly in consequence of entering into the constitution of plants.

Some manures ameliorate a soil by absorbing moisture from theatmosphere. This property is at least as beneficial to ground that is aluminous as to that which is siliceous; for it is equally useless to either during such periods of the year as are characterized by a plentiful deposition of rain; but in the drought of summer, when moisture is much wanting to plants, it is beneficial to both; in very dry seasons it is even of greater importance to clayey than to light soils; for vegetation on the former suffers more from long continued drought than on the latter, inasmuch as that moisture being equally exhaled from each, the surface of the clayey soil becomes caked and impervious to air, the only grand source of compensatory moisture that is available to the languishing plants, and which is more open to those which grow on light, and, consequently, more pervious soils.

The following table of the comparative absorbent powers of many manures, is extracted chiefly from An Essay on the Use of Salt in Agriculture, by Mr. Cuthbert Johnson.

The absorbing power of a manure is much influenced by the state in which it is presented to the atmosphere. In a finely divided state mere capillary attraction assists it; hence, the importance of keeping the soil frequently stirred by hoeing, etc. But a mere mass of cotton, by means of capillary attraction, will absorb moisture from the air, yet it parts with it at a very slight elevation of temperature: it is of importance therefore to ascertain which are the manures that not only absorb but retain moisture powerfully. The following results of my experiments throw some lieht on this point: -

Which by a few hours' exposure to the air subsides into a gray or black hue. The first colour appears to arise from the oxyde of iron which all soils contain, being in the state of the red or protoxide; by absorbing more oxygen during the exposure, it is converted into the black or peroxide. Hence one of the benefits of frequently stirring soils; the roots of incumbent plants abstract the extra dose of oxygen, and reconvert it to the protoxide. Coal ashes, in common with all carbonaceous matters, have the power of strongly attracting oxygen. Every gardener may have observed how rapidly a bright spade of iron left foul with coal ashes, becomes covered with rust, or red oxide.

All animal and vegetable manures absorb oxygen from the air during putrefaction ? If it be required of what benefit this property is to plants, since the gases are freely presented to them in the atmosphere, it admits the ready answer, that they enjoy the additional quantity which is thus collected to the vicinity of their roots, without the latter source being diminished: and that plants are benefited by such additional application to their radiculae has been proved by the experiments of Mr. Hill.

The question may also be asked, whether the roots have the power to extract the oxygen from its combination 1 That they have this power admits of little doubt, since Saussure found that they were able to extract various saline bodies from their combinations; not only extracting but selecting in those cases where several salts were in the same solution.

Dr. Daubeny, the Oxford professor of agriculture, has also shown that stron-tian is rejected by barley, pelargoniums, and the winged pea.

Carbonic acid is also of benefit to plants, when applied to their roots in an advanced stage of their growth. Animal and vegetable matters evolve this gas whilst putrefying; and I am not aware of any manure that absorbs it from the atmosphere, so as to be for that reason beneficial to vegetation. Lime attracts it rapidly, but combines with it so strongly that it is useless to the plant, until the carbonate of lime so formed is imbibed and elaborated.

Manures assist plants by destroying predatory vermin and weeds. This is:

These experiments point out a criterion by which we easily ascertain the comparative richness of any two given soils or manures; the most fertile will be most absorbent and retentive.

Some manures increase the growth and vigour of plants by stimulating their absorbent and assimilating organs.

The stimulating powers of excremen-titious manures arise from the salts of ammonia they contain.

Sir II. Davy found vegetation assisted by solutions of muriate of ammonia (sal-ammoniac), carbonate of ammonia (volatile salt), and acetate of ammonia. Night soil, one of the most beneficial of manures, surpasses all others in the abundance of its ammoniacal constituents in the proportion of three to one. It may be observed, that the nearer any animal approaches to man in the nature, of its food, the more fertilizing is the manure it affords.

I have no doubt that a languishing plant, one, for example, that has been kept very long with its roots out of the earth, as an orange tree recently imported from Italy, might be most rapidly recovered, if its stem and branches were steeped in a tepid weak solution of carbonate of ammonia, and when planted, an uncorked phial of the so-lution were suspended to one of the branches, to impregnate the atmosphere slightly with its stimulating fumes.

Manures are also of benefit to plants by affording some of the gases of the atmosphere to their roots in a concentrated form. A soil, when first turned up by the spade or plough, has generally a red tint, of various intensity, not a property of animal and vegetable manures - they foster both those enemies of our crops. Salt and lime are very efficient destroyers of slugs, snails, grubs, etc.

Stable manure, and all decomposing animal and vegetable substances, have a tendency to promote the decay of stubborn organic remains in the soil, on the principle that putrescent substances hasten the process of putrefaction in other organic bodies with which they come in contact. Salt, in a small proportion, has been demonstrated by Sir J. Pringle to be gifted with a similar septic property, and that lime rapidly breaks down the texture of organized matters is well known.

There is no doubt that rich soils, or those abounding in animal and vegetable remains, are less liable to change in temperature with that of the incumbent atmosphere, than those of a poorer constitution. This partly arises from causes explained when treating of the influence of the colour of soils upon vegetation. Some manures, as salt, protect plants from suffering by sudden reductions of temperature, by entering in their system; stimulating, and rendering them more vigorous, impregnating their sap, and, consequently, rendering it less liable to be congealed. - Princ. of Gardening.