Seeds are the best adapted to the uses of working animals, because they are rich in all kinds of food required. Aside from their use in the formation of _fat_, proximates of the first class are employed in the lungs, as fuel to keep up animal heat, which is produced (as in fire and decay) by the decomposition of these substances. When the food is insufficient for the purposes of heat, the animal's own fat is decomposed, and carried to the lungs as fuel. The stems, roots, branches, etc., of most plants consist principally of _woody fibre_. Their seeds, and sometimes their roots, contain considerable quantities of _starch_. [Name the parts of the plant in which the different proximates exist. State what you know about flour. Do we know that different plants have ashes of different composition?] The _protein_ and the _oils_ of most plants exist most largely in the _seeds_. The location of the proximates, as well as of the inorganic parts of the plant, show a remarkable reference to the purposes of growth, and to the wants of the animal world, as is noticed in the difference between the construction of the straw and that of the kernel of wheat. The reason why the fine flour now made is not so healthfully nutritious as that which contained more of the coarse portions, is that it is robbed of a large proportion of protein and phosphate of lime, while it contains an undue amount of starch, which is available only to form fat, and to supply fuel to the lungs. Different plants have ashes of different composition. Thus--one may take from the soil large quantities of potash, another of phosphoric acid, and another of lime. By understanding these differences, we shall be able so to regulate our rotations, that the soil may not be called on to supply more of one ingredient than of another, and thus it may be kept in balance. [How are farmers to be benefited by such knowledge?] The facts contained in this chapter are the _alphabet of agriculture_, and the learner should not only become perfectly familiar with them, but should also clearly understand the _reasons_ why they are true, before proceeding further. SECTION SECOND. THE SOIL. CHAPTER I. FORMATION AND CHARACTER OF THE SOIL. [What is a necessary condition of growth?] In the foregoing section, we have studied the character of plants and the laws which govern their growth. We learned that one necessary condition for growth is a fertile soil, and therefore we will examine the nature of different soils, in order that we may understand the relations between them and plants. [What is a fixed character of soils? How is the chemical character of the soil to be ascertained? What do we first learn in analyzing a soil? How do the proportions of organic or inorganic parts of soils compare with those of plants? Of what does the organic part of soils consist?]