The cellulose of the slime-mould looks toward the world of plants. The aerial fructification and stipitate habit of the higher forms tends in the same direction. The disposition to attach themselves to some fixed base is a curious characteristic of plants, more pronounced as we ascend the scale; but by no means lacking in many of the simplest, diatoms, filamentous algae, etc., and it is quite as reasonable to call a vorticella, or a stentor, by virtue of his stipitate form and habit, a plant as to call a slime-mould an animal because in one stage of its history it resembles an amoeba. The total life of an organism in any case must be taken into account.[11] At the outset plants and animals are alike; there is no doubt about it; they differ in the course of their life-histories. The plasmodium is the vegetative phase of the slime-mould. It needs no cell-walls of cellulose, no more than do the dividing cells of a lily-endosperm; both are nourished by organic food and resort to walls only as conditions change. The possession of walls is an indication of some maturity. In the slime-mould the assumption of walls is indeed delayed. Walls at length appear and when they do come they are like those of the lily; they are cellulose. The myxomycetes may be regarded as a section of the organic world in which the forces of heredity are at a maximum whatever those forces may be. Slime-moulds have in smallest degree responded to the stimulus of environment. They have, it is true, escaped the sea, the fresh waters in part, and become adapted to habitation on dry land, but nothing more. It is instructive to reflect that even in her most highly differentiated forms the channel which Nature elects for the transmissal of all that heredity may bestow, is naught else than a minute mass of naked protoplasm. Nature reverts, we say, to her most ancient and simple phases, and heredity is still consonant with apparent simplicity; apparent we say, for as becomes increasingly evident, nothing that lives is simple!