Open an outlet for the water below, and as it trickles away, the air from above will follow it and take its place among the pores of the soil, carrying to every root the salutary influences it is appointed to bear with it wherever it penetrates. When freed from water also, the stiff soil becomes more mellow; and when once stirred up to a considerable depth, more universally porous,—so that air can make its way everywhere, and the roots can find their easy way in every direction. The presence of vegetable matter,—whether existing naturally in a soil thus physically altered, or artificially added to it,—becomes of double value. When drenched with water, this vegetable matter either decomposes very slowly, or produces acid compounds more or less unwholesome to the plant, and even exerts injurious chemical reactions upon the earthy and saline constituents of the soil. In the presence of air, on the contrary, this vegetable matter decomposes rapidly, produces carbonic acid in large quantity, as well as other compounds fit for food, and even renders the inorganic constituents of the soil more fitted to enter the roots, and thus to supply more rapidly what the several parts of the plant require. Nor is it only stiff and clayey soils to which draining can with advantage be applied. It will be obvious to every one, that when springs rise to the surface in sandy soils, a drain must be made to carry off the water,—it will also readily occur, that where a sandy soil rests upon a hard or clayey bottom, drains may also be necessary; but it is not unfrequently supposed, that when the subsoil is sand or gravel, that drains can only in special cases be necessary. Every one, however, is familiar with the fact, that when water is applied to the bottom of a flower-pot full of soil, it will gradually find its way to the surface, however light the soil may be. So it is in sandy soils or subsoils in the open field. If water abound at the depth of a few feet, or if it so abound at certain seasons of the year, _that_ water will rise to the surface; and as the sun’s heat dries it off by evaporation, more water will follow to supply its place. This attraction from beneath will always go on when the air is dry and warm, and thus a double evil will ensue—the soil will be kept moist and cold, and instead of a constant circulation of air downwards, there will be a constant current of water upwards. Thus will the roots, the under soil, and the organic matter it contains, be all deprived of the benefits which the access of the air is fitted to confer. The remedy for these evils is to be found in an efficient system of drainage.