1251. Every species of matter capable of promoting the growth of vegetables may be considered as manure. On examining the constituents of vegetables, we shall find that they are composed of carbon, oxygen, hydrogen, and nitrogen, or azote, with a small proportion of earthy and saline matters, which, however, are as essential to the health of the plants as all the other elements combined. It is obvious that when a soil is deficient in any of the elements required, they should be supplied to it; and as the substances thus supplied are all included under the general name of manure, it is obvious that manures must be of many different kinds, particularly as none of the elements required can be presented to the plants in a pure state, being always found in combination with other elements, from which they require to be freed before they can form the new combinations necessary to make them available as food for plants.
