Green Manure is a mass of recently growing plants dug whilst green, and fresh into the soil, for the purpose of enriching it; and it is a rule without any exception, that all fresh vegetable matters so turned into the earth do render it more fertile, and if plants are grown upon the soil for this purpose, the greater the amount of the surface of leaves in proportion to that of roots the better, because such plants obtain .1 large proportion of their chief cotistituent, - the chief constituent of all plants, carbon, - from the atmosphere: they, therefore, return to the soil more decomposing matter than they have taken from it.

The putrefaction of the vegetables, and the gases in that case emitted, says my brother, Mr. Cuthbert Johnson, "appear to be on all occasions highly invigorating and nourishing to the succeeding crop. During this operation, the presence of water is essentially necessary, and is most probably decomposed. The gases produced vary in different plants; those which contain gluten emit ammonia; onions and a few others evolve phosphorus; hydrogen, carbonic acid gas, and carburetted hydrogen gas, with various vegetable matters, are almost always abundantly formed. All these gases when mixed with the soil are very nourishing to the plants growing upon it. The observations of the farmer assure us that they are so. He tells us that all green manures cannot be employed in too fresh a. state, that the best corn is grown where the richest turf has preceded it, and that where there is a good produce of red clover there will assuredly follow an excellent crop of wheat; he finds also that when he ploughs in his crop of buckwheat to enrich his land, that this is most advantageously done when the plant is coming into flower." - Farm. Encyc.

Sea Weed is a species of green manure, for it ought to be employed whilst quite fresh. There are many species, and they differ very essentially in their components. The Laurinariee, those long, tawny-green, ribbon-like algae so common on our coasts, contain besides vegetable matter a large proportion of the salts of potash in addition to those of soda; whereas the Fuci contain none of the salts of potash. All, however, are excellent manures, and I know a garden, near Southampton, very productive, that for some years has had no other manure. It is particularly good as a manure for potatoes. The Facus vesiculosus, so distinguishable by the bladders full of air embedded in its leaves, is a very excellent manure. It contains, when dry, about 84 parts vegetable matter, 13 parts sulphate of lime and magnesia, with a little phosphate of lime, and 3 parts sulphate and muriate of soda.

The advantage of green manure is practically understood by thousands of our farmers, who, though they may be unable to philosophize upon the subject or refer to its true chemical cause, fully appreciate its value.

The great desideratum of those who aim at enriching the soil, is to produce clover, - that attained, the rest is easy. Clover, when turned in, prepares the land for every description of crop, and places the whole under the control of the husbandman.