food,"
etc., as applied to the nutrition and growth of plants. Strictly speaking,
these terms ought probably to be limited in their application to the
organized compounds within the plant which it uses as sources of energy and
of metabolizable material for the development of new cells and organs
during its growth. Botanists quite commonly use the terms in this way. But
students of the problems involved in the relation of soil elements to the
growth of plants, including such practical questions as are involved in the
maintenance of soil productivity and the use of commercial fertilizers for
the growing of economic plants, or crops, are accustomed to use the terms
"plant foods," or "mineral nutrients," to designate the chemical elements
and simple gaseous compounds which are supplied to the plant as the raw
material from which its food and tissue-building materials are synthetized.
Common usage limits these terms to the soil elements; but there is no
logical reason for segregating the raw materials derived from the soil from
those derived from the atmosphere.

The essential difference between these raw materials for plant syntheses
and the organic compounds which are produced within the plants and used by
them, and by animals, as food, is that the former are inorganic and can
furnish only materials but no energy to the organism; while the latter are
organic and supply both materials and potential energy. It would probably
be the best practice to confine the use of the word "food" to materials of
the latter type, and several attempts have been made to limit its use in
this way and to apply some such term as "intake" to the simple raw
materials which are taken into the organism and utilized by it in its
synthetic processes. But the custom of using the words "food," or
"nutrient," to represent anything that is taken into the organism and in
any way utilized by it for its nourishment has been followed so long and
the newer terms are themselves so subject to criticism that they have not
yet generally supplanted the loosely used word "food."

If such use is permitted, however, it is necessary to recognize that only
the green parts of green plants can use this inorganic "food," and that the
colorless plants must have organic food.

To avoid this confusion, the suggestion has recently been made that all of
the intake of plants and animals shall be considered as food, but that
those forms which supply both materials and potentia