3. But this is not all; for the addition of a superior function requires not only the addition of an organ having a corresponding superiority of structure, but it requires, further, that a certain elevation of structure should be communicated to all the organs of all the inferior functions, on account of the relation which it is necessary to establish between function and function. Unless the organ of an inferior function be constructed with a perfection corresponding to that of the organ of a superior function, the inferior will be incapable of working in harmony with the superior. Take, for example, the inferior function of nutrition: nutrition is an organic function equally necessary to the plant and to the animal, and requiring in both organs for performing it; but this function cannot be performed in the animal by organs as simple as suffice for the plant. Nutrition, in the plant, is carried on in the following mode:—The root of the plant is divided, like the trunk, into numerous branches (fig. I. 1). These branches divide and subdivide into smaller and smaller branches, until at last they reach an extreme degree of minuteness (fig. I. 2 2). The smallest of these divisions, called, from their hair-like tenuity, _capillary_ (fig. I. 2 2), are provided with a peculiar structure, which is endowed with a specific function. In most plants this peculiar structure is found at the terminal point of the rootlet (fig. I. 2 2); but in some plants the capillary branches of the rootlets are provided with distinct bodies (fig. II. 1 2), scarcely to be discerned when the root has been removed some time from the soil, and has become dry (fig. II. 2 2); but which, in a few minutes after the root has been plunged in water, provided the plant be still alive, become turgid with fluid, and, consequently, distinctly visible (fig. II. 1 1 1). These bodies, when they exist, or the terminal point of the rootlet when these bodies are absent, are termed _spongeolæ_, or spongeoles; and the structure and function of the organ, in both cases, are conceived to be precisely the same. In both the organ consists of a minute cellular structure. Fig. III. 1, shows this structure as it appears when the object is magnified. The office of this organ is to absorb the aliment of the plant from the soil; and so great is its absorbing power, that, as is proved by direct experiment, it absorbs the colouring molecules of liquids, though these molecules will not enter the ordinary pores, which are of much greater magnitude. With the spongeoles are connected vessels which pass through the substance of the stem or trunk to the leaf. Fig. III. 2, shows these tubes springing from the cellular structure of the spongeole, and passing up to the stem or trunk. Fig. IV. 2, exhibits a magnified view of the appearance of the mouths of these tubes on making an horizontal section of the spongeole. Fig. V. 1 1 1, exhibits a view of these tubes passing to the leaf. Figs. VI. and VII.