The labors of modern chemists have shown us, and it is one of their grandest discoveries, that it is the Azote to which manures owe all their value, and that their fertilizing properties are just in proportion to the quantity of this agent they contain. It is not always in its form of a simple body that this gas is useful; it can only be absorbed by plants in combination with hydrogen, that is to say, in the condition of ammonia. It has also been satisfactorily demonstrated that the atmosphere is the grand source or medium from whence vegetables derive this substance. Hence the great utility of cultivated plants being trenched in the soil, especially if these plants are such as easily give off their azote to mix in the atmosphere rather than in the soil. Leguminous plants, for instance, are very suitable in this respect; and long experience rather than ing, has not made this discovery, hut it has elucidated and justified a practice long in use. It may be interesting to investigate thecaums which perpetuity hold in the atmosphere the quantity of ammonia necessary for the develop-ment of vegetables, and which repair without ceasing the losses which they sustain.

According to the researches of many chemists, and particularly those of M.M. Boussingault and Liebig. these causes are two in number. The one which is the most direct is the decomposition of organized bodies, which, without exception, contain a greater or less quantity of azote. All vegetables contain it, but it is particularly in the bodies of animals that this agent is condensed. It enters extensively into the composition of their organs, and when, after death, these animals are left to the chemical action of nature, all the elements of which they are constituted separate, and immediately form new, and, for the greater part, gaseous compounds, and among others the ammonia, which returns to the atmosphere, where it soon dissolves in the watery vapor with which the air is always charged.

The second productive cause of atmospheric ammonia has been much less studied, and it is only within a few years that its existence has been suspected. It is known to reside in the electric discharges which succeed one another in the air, at least in certain portions of the globe. It is the opinion of Boussingault as well as of the celebrated Liebig, that the carbonate of ammonia must pre-exist in all organised beings. "The phenomenon of the constancy of thunder-storms," says M. Boussingault in his treatise on Rural Economy, "would seem to justify this opinion." It is said, indeed, that every time a series of electric flashes pass in the humid atmosphere, there is a production and combination of nitric acid and ammonia. The nitrate of ammonia, besides, always accompanies the rain which falls in a thunder-storm; but this acid being fixed in its nature cannot be maintained in a state of vapor. When we consider the reactions which take place between the different compounds in question, it may easily be conceived that the nitrate of ammonia, which is drawn to the earth by the rain, and which comes in contact with the rocks or calcareous soil, is afterwards volatilised to the state of carbonate at the next drying of the soil.

In such a climate as France, where thunder-storms are rare, we should perhaps scarcely attach so much importance to the electricity of the clouds; but, between the tropics, the electric discharges which take place in the atmosphere are almost incessant, and an observer placed at the equator, if his organ of sound were delicate enough, would hear the peals of thunder continually. There can be no doubt at the present day, that the carbonate of ammonia is the most active agent of vegetation and without which he to try to create an atmosphere of the carbonate of ammonia under his ground, would spend a great deal of money without obtaining any benefit whatever, since the slightest movement of the air would instantly produce evaporation of this volatile manure." It is fortunate then, that so useful an agent can be insured for the purposes of horticulture wherever a quantity of the air can be isolated from the air outside; yet it is somewhat singular that its use, now attracting attention, in the cultivation of plants in the green-house, stove, pit and frame, has not been thought of sooner. - Revue Horticole.