c acid occurs in the soil almost entirely in
an _insoluble_ form; and when applied to the soil in a soluble form, is
speedily converted into an insoluble condition. Its most commonly
occurring forms are as phosphates of lime, iron, and alumina. These
facts are of importance to remember, as they explain why phosphoric acid
is not found in drainage-water in any quantity. It also shows how little
the risk of loss from drainage is in the application of artificial
phosphatic manure to the soil.

_Occurrence in Plants._

The percentage of phosphoric acid in plants, like other
ash-constituents, is subject to considerable variation, and depends on a
variety of conditions, such as the state of the plant's development,
nature of soil, climate, season, treatment with manures, &c. All these
conditions have a certain influence. The different parts of the plant
have been found to contain it in different quantities. The tendency of
phosphoric acid is to travel up to the higher portions of the plant with
the progress of growth, and to finally accumulate in the seed. As
illustrating this, it may be mentioned that the inner portion of the
stalk of a ripe oat-plant has been found to contain only a seventeenth
of the amount of phosphoric acid found in the same portion of the stalk
of a young oat-plant. Similarly it may be mentioned that, while the ash
of the grain of rye and wheat contains nearly half their weight of
phosphoric acid, the percentage present in the ash of other parts of the
plant amounts only to from 5 to 16 per cent. The percentage of
phosphorus is greater in young plants than in mature plants; it is
greater also in quickly developed plants than in slowly developed
plants.

In the plant, phosphorus is present chiefly in the albuminoids; and its
absorption from the soil takes place in greatest quantity during the
period of maximum growth. In beans and peas an oil containing phosphorus
has been found.

_Occurrence in Animals._

That phosphorus in different forms exists in animal tissue is well
known. It is found both in the brain and in the nerves, as well as in
nearly all the fluids of the animal body. It is, however, in the bones
that it is most abundant, the mineral portion of which is almost
entirely made of phosphate of lime,--a fact which renders bones such a
valuable artificial manure. Altogether, phosphoric acid occurs in the
animal body to the extent of 2.3 per cent. There is a point which we
shall have oc