thinking about our own real problems. Even in the country schools we
have learned something of banking and various other lines of
business, something of the history and politics of this and other
countries, something of the great achievements in war, in discovery
and exploration, in art, literature, and invention; but we have not
learned what our soils contain nor what our crops require. Not one
farmer in a hundred knows what chemical elements are absolutely
required for the production of our agricultural plants, and one may
work hard on the farm from four o'clock in the morning till nine
o'clock at night for forty years and still not learn what corn is
made of.

"All agricultural plants are composed of ten chemical elements, and
the growth of any crop is absolutely dependent upon the supply of
these plant food elements. If the supply of any one of these plant
food elements is limited, the crop yield will also be limited. The
grain and grass crops, such as corn, oats, wheat, and timothy, also
the root crops and potatoes, secure two elements from the air, one
from water, and seven from the soil.

"The supply of some elements is constantly renewed by natural
processes, and iron, one of the ten, is contained in all normal
soils in absolutely inexhaustible amount; while other elements
become deficient and the supply must be renewed by man, or crop
yields decrease and farming becomes unprofitable.

"Matter is absolutely indestructible. It may change its form, but
not a pound of material substance can be destroyed. Matter moves in
cycles, and the key to the problem of successful permanent
agriculture is the circulation of plant food. While some elements