The nutritive substances in crops
The dry matter of all plants and plant parts consists of three very
distinct classes of substances: First, ash or the mineral
constituents. Ash is used by the body in building bones and in
supplying the blood with compounds essential to the various life
processes. Second, protein or the substances containing the element
nitrogen. Protein is used by the body in making blood, muscle,
tendons, hair, and nails, and under certain conditions it is burned
within the body for the production of heat. Protein is perhaps the
most important food constituent. Third, non-nitrogenous substances,
including fats, woody fiber, and nitrogen-free extract, a name given
to the group of sugars, starehes, and related substances. These
substances are used by the body in the production of fat, and are
also burned for the production of heat. Of these valuable food
constituents protein is probably the most important, first, because
it forms the most important tissues of the body and, secondly,
because it is less abundant than the fats, starches, and sugars.
Indeed, plants rich in protein nearly always command the highest
prices.
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