it is better to combine them than to endeavor to subsist on one only.

Whither, then, go these elements when man has done with them? The answer
is,--All Nature wants them. Every plant is ready to drink them up, as
soon as they have taken forms which bring them within its reach. As
gases, they are inhaled by the leaves, or, dissolved in water, they
are drunk up by the roots. All plants have not the same appetites, and
therefore they can make an amicable division of the supply. Grasses and
grains want a large proportion of phosphate of lime, which they convert
into husks. Peas and beans have little use for nitrogen, and resign it
to others. Cabbages, cauliflowers, turnips, and celery appropriate a
large share of the sulphur.

The food of plants and that of animals have this great difference:
plants take their nourishment in inorganic form only; animals require
to have their food in organic form. That is, all the various
minerals, singly or combined, which compose the tissues of plants and
animals,--carbon, hydrogen, phosphorus, and the rest, which we have
already named,--are taken up by plants in mineral form alone. The food
of animals, on the other hand, consists always of organized forms. There
is no artificial process by which oxygen, carbon, and hydrogen can be
brought into a form suitable for the nourishment of animals. As oxygen,
carbon, and hydrogen, they are not food, will not sustain our life,
and human art cannot imitate their nutritious combinations. Artificial
fibrine and gluten (organic principles) transcend our power of
contrivance as far as the philosopher's stone eluded the grasp of the
alchemists. We know exactly how many equivalents of oxygen, hydrogen,
carbon, and nitrogen enter into the composition of each of the animal
elements; but we can no more imitate an organic element than we can form
a leaf. What we cannot do the vegetable world does for us. Thus we see