Biology

ies which enter into the composition of the plant and into that of the animal. We shall glance very rapidly at the immediate principles of the first category. In effect, water, which constitutes in weight the largest part of organised beings, mineral salts, atmospheric gases, are manifestly unable to furnish to us sufficiently distinctive characteristics. But that the results of the comparison may be the more striking we shall indicate first of all in bold outline what is the chemical composition of plants, and what is that of animals. 1. Chemical Composition of Plants. Organised vegetal tissues, when submitted to desiccation, present a friable residuum, the weight of which is very variable. ]n the average of terrestrial plants this residuum is from a fifth to a third of the total weight ; but it rises to eight-ninths if we take ripe seeds, and can descend to a tenth or a twentieth in aquatic plants and certain mushrooms. This residuum, desiccated, offers always to chemical analysis, carbon, hydrogen, oxygen, azote and sulphur, potassium, calcium, magnesium, iron, phosphorus. Often, moreover, we find therein sodium, lithium,manganese, silicium, chlore. Finally, in the marine plants we discover iodine and brome. Such are the ultimate results of analysis; but, of course, during life, these bodies are not, for the most part, in a state of liberty; they are combined in various manners. The metals are usually in the state of salts, of sulphates, of phosphates,...