The facts which have been reviewed concerning the elements out of which the tissues of plants and animals are built are properly supplemented by a statement of the proportions in which these are found in living organisms. This information is necessary to an understanding of the relations of supply and demand which exist between the vegetable and animal kingdoms and the raw materials of the inorganic world.

17. In Plants

It is estimated by a German scientist, Knop, that if all the species of the vegetable kingdom, exclusive of the fungi, were fused into one mass, the ultimate composition of the dry matter of this mixture would be the following: -

The composition of various plant substances used as human food shows considerable variations from these average figures.

Carbon constitutes a larger proportion of the dry substance of plants than any other element, and there is certainly no species that is an exception to this rule. Oxygen stands next in order, followed by hydrogen, and then nitrogen. It is an important fact in the economy of nature that those elements which, on the average, make up 93.5 per cent of the dry matter of plants have as their main source either the atmosphere or water. Only a small percentage of the dry matter of food plants is drawn from the dry matter of the soil, and it is this part of plant substance which is economically important to those engaged in the production of human food.

The elements of the ash vary somewhat in different plants or parts of plants. For illustration, their proportions in the dry matter of several kinds of plant substance that enters into the human diet are given in this connection:

Table II. Ash Elements In Cereal Grains And Vegetables

1 Calculated from Wolff's " Aschen Analysen."