e proportion of the total supply is deposited in
them.

Nitrates are the normal form of nitrogen in the soil which is available to
plants. During germination and early growth, the young seedling uses
amino-acids, etc., derived from the proteins stored in the seed, as its
source of nitrogen; and experiments have shown that similar forms of
soluble organic nitrogen compounds can be successfully fed to the seedling
as an external food supply. Soluble ammonium salts can be utilized as
sources of nitrogen by most plants during later periods of growth,
particularly by the legumes. But for most, if not all, of the common farm
crops whose possibilities in these respects have been studied, it has been
found that a unit of nitrogen taken up as a nitrate is very much more
effective in promoting growth, etc., than is the same unit of nitrogen in
the form of ammonium salts.

While the proteins are finally stored up largely in the seeds, or other
storage organs, they are actively at work during the growing period in the
cells of the foliage parts of the plant. Hence, the popular statement that
"nitrogen makes foliage" is a fairly accurate expression of its role.
Inordinate production of straw in cereal crops and of leaves in root crops
often results from liberal supplies of available nitrogen in the soil early
in the growing season. If the crops develop to normal maturity, this
excessive foliage growth has no harmful results, as the surplus material
which has been elaborated is properly translocated into the desired storage
organs; but, unfortunately, the retarding effect of the surplus nitrogen
supply upon the date of maturing of the crop is often associated with
premature ripening of the plants from other causes, with the consequence
that too large a proportion of the valuable food material is left in the
refuse foliage material of the crop. Crops which are grown solely for their
leaves, such as hay crops, lettuce, cabbage, etc., profit greatly by
abundant supplies of available nitrogen; although when foliage growth is
stimulated in this way the tissue is likely to be thin-walled and soft
rather than firm and solid.

=Phosphorus= is likewise an extremely important element in plant nutrition.
But phosphorus starvation produces no such striking visible effects upon
the growth of the plant as does lack of nitrogen. Abundance of available
phosphorus early in the plant's life greatly stimulates root growth, and
later on it undoubtedly