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 why it was necessary that the earth should be clothed with vegetation before animals could be introduced. A field-mouse dies and decays, and its elements are appropriated by the roots around its grave; and we can easily imagine the next generations of mice, the children and grandchildren of the deceased rodent, feasting off the tender bark which was made out of the remains of their parent. The soil of our gardens and the atmosphere above it are full of potential tomatoes, beans, corn, potatoes, and cabbages,--even of peaches of the finest flavor, and grapes whose aroma is transporting.