[Footnote 15: See, _e.g._ Sir Alexander Grant's _Aristotle_ in the Ancient Classics for English Readers Series (Blackwood), pages 119-121.] This gives us, too, the clue to the distinction between {296} the inorganic and the organic. If inorganic matter is what has its end outside itself, organic matter will be what has its end within itself. This is the essential character of an organism, that its end is internal to it. It is an inward self-developing principle. Its function, therefore, can only be the actualisation, the self-realization of this inward end. Whereas, therefore, inorganic matter has no activity except spatial movement, organic matter has for its activity growth, and this growth is not the mere mechanical addition of extraneous matter, as we add a pound of tea to a pound of tea. It is true growth from within. It is the making outward of what is inward. It is the making explicit of what is implicit. It is the making actual of what is potential in the embryo organism. The lowest in the scale of being is thus inorganic matter, and above it comes organic matter, in which the principle of form becomes real and definite as the inward organization of the thing. This inward organization is the life, or what we call the soul, of the organism. Even the human soul is nothing but the organization of the body. It stands to the body in the relation of form to matter. With organism, then, we reach the idea of living soul. But this living soul will itself have lower and higher grades of being, the higher being a higher realization of the principle of form. As the essential of organism is self-realization, this will express itself first as self-preservation. Self-preservation means first the preservation of the individual, and this gives the function of nutrition. Secondly, it means preservation of the species, and this gives the function of propagation. The lowest grade in the organic kingdom will, therefore, be {297} those organisms whose sole functions are to nourish themselves, grow, and propagate their kind. These are plants. And we may sum up this by saying that plants possess the nutritive soul. Aristotle intended to write a treatise upon plants, which intention, however, he never carried out. All that we have from him on plants is scattered references in his other books. Had the promised treatise been forthcoming, we cannot doubt what its plan would have been. Aristotle would have shown, as he did in the case of animals, that there are higher and lower grades of organism within the plant kingdom, and he would have attempted to trace the development in detail through all the then known species of plants.