numerous substances which contain these elements in greater or less
degrees
The food of plants consists of chemical elements, or rather, of
numerous substances which contain these elements in greater or less
degrees. There is not room here to go into the interesting science of
this matter. It is evident, however, as we have already seen that the
plants must get their food from the soil, that there are but two
sources for such food: it must either be in the soil already, or we
must put it there. The practice of adding plant food to the soil is
what is called manuring.