Nitrogen is usually absorbed in greater amounts than any
other element. Lack of it from the beginning causes diminu-
tive plants with comparatively larger root systems, smaller and
lighter colored leaves, and drier leaf tips than the normal plant.
It does not in general interfere with the processes essential for
growth in plants like wheat, whose seed contains enough nitro-
gen to produce another seed in a small plant. When nitrogen
is deficient, growth proceeds normally but on a diminutive
scale. But plants with small seed, like lettuce, cannot repro-
duce unless they are provided with this element.
Many species can reproduce from the original fund of nitro-
gen contained in their seed or seedlings without additional sup-
plies from outside sources. Seed from such plants will germi-
nate but cannot itself produce viable seed. Many cereal grains
are in this class. They show increases in growth directly pro-
Symptoms of Change
Proportional to additions of nitrogen to the solution until an ex-
cess of nitrogen becomes available. Then the ratio is no longer
consistent. The excess produces very lush vegetation with a
corresponding decrease in the firmness of stems and leaves.
Foliage is produced rapidly at the expense of root growth, the
ratio of fruit or seed to vegetation is subnormal, and the con-
formation of plant parts is off-type.
In an experiment with wheat reacting to lack and excess of
nitrogen, the ratio of grain to total weight of plant when ni-
trogen was deficient was 15 per cent (i, 2, 3) . When the
element was in excess, the same ratio was 20 per cent (6, 7) .
In a culture from which nitrogen was removed when the plants
were three months old, the ratio was 30 per cent (4, 5) . When
nitrogen was lacking, the plants did not produce enough foliage
and were unable to manufacture the starch needed for the
kernels. When an excess of the element was present, too much
foliage was produced; that is, vegetative growth continued too
Symptoms of Change
This also cut down the production of grain. Starch for
the kernels is not produced from new leaves but only from
those which have attained some size. If a high production of
grain is to be obtained, it is necessary for the plants to stop
forming new leaves after they have attained size. Thus, by
prolonging vegetative growth the nitrogen excess inhibits the
formation of the kernels.
This tendency of nitrogen to cut down the storage of starch
and sugar is not so important for some flowers and crops grown
chiefly for their leafy tissue. However, they may also absorb