ufficient supply is present. The production and storage of sugar,
or starch, in such root crops as beets, potatoes, etc., diminishes in
direct proportion with a decreasing supply of potassium as plant food. The
grains of the cereal crops become shrunken as a result of potassium
starvation; and are plump and well filled with starch in the endosperm when
sufficient potassium is available for the crop's needs.

The general tone and vigor of growth of the plant is largely dependent upon
an ample potassium supply; potash-hungry plants, like those which have been
weakened by any other unfavorable conditions, have been found to be more
susceptible to injury by disease, than those which are well nourished with
this food element. But potassium-starvation does not produce any
pathological condition of the cell contents; its absence simply prevents
the possibility of the development of the necessary carbohydrates for
vigorous growth.

There is no known difference in the availability, or effectiveness, of
potassium from the different forms of compounds containing it which may be
present in the soil. Apparently, the only essential is that the compound
shall be soluble so that it can be absorbed into the plant through the
root-hairs. Of course, the acid radical to which the basic potassium ion is
attached may, in itself, have some beneficial or deleterious influence
which gives to the compound as a whole some important effect in one case,
which might not follow in the case of another type of compound; but the
relative efficiency as plant food of a given unit of potassium seems to be
the same regardless of the nature of the compound in which it is present.

=Calcium= is an essential plant food element but its physiological use has
not yet been definitely established. It seems to stimulate
root-development, and certainly gives vigor and tone to the whole plant. It
is commonly believed that calcium is in some way connected with the
development of cell-wall material. It has been reported that the stems of
grasses and cereal plants become stiffer in the presence of ample calcium,
but this may be due to greater turgidity rather than to strengthened
cell-walls. Calcium remains in the leaves or stem as the plant ripens, but
it is not clear that this has anything to do with the stiffness or weakness
of the stem, or straw, of the plant. Experiments with algae have shown that
in the absence of calcium salts mitotic cell division takes place, sh