The germ itself is also a very nutritious food for man; hence the seed is eaten, "baby and all." In the corn, those kernels with the largest germs have the largest food value, and, therefore, to-day corn breeders are developing kernels with very large embryos. If we examine the microscopic structure of the food part of a grain of wheat (Fig. 280), we find that there are two outer layers, _a_ and _b_. Next there is a row of cells _d_ that divides these outer layers from the flour cells within. This is the aleurone layer. At _e_ are the flour cells which constitute the central portion of the wheat kernel. They contain starch, and also gluten, and some oil, and some mineral substances. In grinding to make white flour, the miller tries to leave the aleurone layer of cells _d_ with the outer layers _a_ and _b_, for if it is mixed with the flour the latter spoils much sooner, and it is also darker in color. In the seed is a ferment that helps digest the food for the young plant. [Illustration: _Fig. 280. Section of grain of wheat._] In order to think more intelligently about our use of food, let us find out, if we can, which parts of the food stored up by the plant for its sustenance are used by us both for ourselves and our livestock. The intelligent farmer gives his stock a carefully balanced ration, _i. e._, food that is well proportioned for the growth and product of the animal. If he wishes his cows to give more milk he may give them more proteids in their food, and less starch and fat. If he wishes to fatten them he may give them a greater amount of starch and fat and less of the proteids. In order to know what these proteids and starch and fat mean, both to us and to the plant, we have to know a little chemistry. The following table may aid us in this: Nutritive substances which {Proteids (casein, gluten, legumen, contain nitrogen. { etc., albuminoids, gelatine, { white of egg, etc.). Nutritive substances which {The carbohydrates (sugar and do not contain nitrogen. { starch). Fats (oils, butter). Mineral substances. {Lime, phosphorus, sulfur, etc.