How does it hold water for the uses of the plant? How does it obtain a part of its moisture?] The mechanical character of the soil is well understood from preceding remarks, and the learner knows that there are many offices to be performed by the soil aside from the feeding of plants. 1. It admits the roots of plants, and holds them in their position. 2. By a sponge-like action, it holds water for the uses of the plant. 3. It absorbs moisture from the atmosphere to supply the demands of plants. [How may it obtain heat? What is the use of the air circulating among its particles? Could most soils be brought to the highest state of fertility? What is the first thing to be done? Should its color be darkened?] 4. It absorbs heat from the sun's rays to assist in the process of growth. 5. It admits air to circulate among roots, and supply them with a part of their food, while the oxygen of that air renders available the minerals of the soil; and its carbonic acid, being absorbed by the water in the soil, gives it the power of dissolving, and carrying into roots more inorganic matter than would be contained in purer water. 6. It allows the excrementitious matter thrown out by roots to be carried out of their reach. All of these actions the soil must be capable of performing, before it can be in its highest state of fertility. There are comparatively few soils now in this condition, but there are also few which could not be profitably rendered so, by a judicious application of the modes of cultivation to be described in the following chapters. The three great objects to be accomplished are:-- 1. To adopt such a system of drainage as will cause all of the water of rains to pass _through_ the soil, instead of evaporating from the surface. 2. To pulverize the soil to a considerable depth. 3. To darken its color, and render it capable of absorbing atmospheric fertilizers. [Name some of the means used to secure these effects. Why are under-drains superior to open drains?] The means used to secure these effects are _under-draining, sub-soil and surface-plowing, digging, applying muck, etc._ CHAPTER II. UNDER-DRAINING. The advantages of _under_-drains over _open_ drains are very great. When open drains are used, much water passes into them immediately from the surface, and carries with it fertilizing parts of the soil, while their beds are often compacted by the running water and the heat of the sun, so that they become water-tight, and do not admit water from the lower parts of the soil. The sides of these drains are often covered with weeds, which spread their seeds throughout the whole field. Open drains are not only a great obstruction to the proper cultivation of the land, but they cause much waste of room, as we can rarely plow nearer than within six or eight feet of them.