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25, 1864.] the earth and atmosphere, those two grand and inexhaustible store-houses of vegetable food. The commencement of this epoch is therefore marked by the atrophy and fall of the nursing leaves. See, how admirably the two extremities of our plant are organically adapted to the earth and atmosphere! A rootlet and a leaf, how different in form and colour! yet both are absorbents beautifully adapted to the two media into which they develope themselves. Their functions are the same. We cannot, in a paper like the present, undertake to enter minutely into the anatomy and physiology of these organs. Let it be remembered that this is only a brief outline of plant-life, sufficient to awaken, we hope, a pleasing train of thought in the mind of the reader. It is enough then if we simply state the facts. The little rootlets descend into the soil, and put forth from their surface innumerable fine white, hair-like fibres, which are the instruments by means of which the plant takes up its food; its young stem ascends into the air, and its bark and fibre, arranged cylindrically in separate beds or Layers in the stem, are spread out horizontally at definite points along its stem, in the form of numerous fiat, horizontal, green plates, or absorbent surfaces, called leaves. The bark or cellular tissue of these leaves is penetrated by the fibres of the wood in the shape of reins, veinlets and capillaries, which communicate directly with the fibres of the stem and roots, and thus act as conduits of the sap from one extremity of the plant to the other. In this manner the sap brought from all the other parts of the plant is conducted to all parts of the leaf by these veins, veinlets and capillaries, to be thoroughly spread out and aerated in the leaves.

The processes of evaporation and absorption are greatly facilitated by the organisation of the skin, or epidermal covering of the leaves. This skin, with its porous openings, is adapted to the aerial medium by which the leaves are surrounded. The porous openings are called stomata. They are, in fact, self-acting valves, and consist of two cells together, usually of an oval figure, with a slit in the middle. They are so situated as to open directly into the hollow chambers, or air cavities, in the interior of the leaf. It is through these pores that the superfluous water of the sap is evaporated, and such gases absorbed from the atmosphere as are nutritious to the plant.

The structure of the stomata, or pores, may be readily perceived on the epidermis of the lily, where they are unusually large. The epidermis must be carefully removed, and having been freed from its chlorophyl or leaf-green, it must be placed between two strips of glass, with a drop of water between them, so as to give it the necessary degree of transparency. Water ought, for this reason, always to be used, whenever objects selected from the tissues of vegetables are examined microscopically. The epidermis thus prepared will exhibit the pores, and the nature and beauty of their mechanism will be better understood and appreciated.

Hence, when fully formed, these aerial leaves aerate and elaborate the sap or nutritive fluid, in a much more perfect manner than the nursing leaves; and the growth of the plant is consequently more rapid after their evolution.

The leaves now contribute individually to each other’s support, the lower leaves aiding in the growth of those that are above them, and contributing also to the development of that portion of the stem which is below them, and to the increase of the number of rootlets in the soil, and thus vegetative power gradually increases. We have a manifest proof of this in the increase in size of the leaves from below upwards, and also in the increase in the length of the intern odes, or naked intervals of stem which separate them. For the size of the leaves and the length of their internodes depend wholly on the vegetative activity of the leaves themselves; and as those leaves situated towards the middle of the stem are not only larger, but more wide apart, than the leaves above and below them, it is evident that the growth of the plant is first accelerated and then retarded, and that the vegetative force is greatest about the middle of the stem. It is here, therefore, that the wave of growth culminates. From this point upwards the vegetative force diminishes, the leaves decrease in size, their internodes shorten, until finally the vegetative force is reduced to zero, and the leaves are crowded into those beautiful metamorphosed clusters, or rosettes, popularly called flowers. In the flower the wave of growth is depressed to a minimum, for when the flower appears, growth invariably ceases in that direction.

Our plant has now entered upon that interesting period which has been emphatically called “the change of life.” We notice a peculiar alteration in its habits and structure. Another force has come into play—that of reproduction —which gradually gains the ascendency, checks the growth of the plant, brings the leaves together, and finally culminates in the production of flower-buds. These differ only from leaf-buds in having no power of extension, for as in the flower the vegetative powers of the leaves are reduced to zero, the axis of the floral leaves necessarily retains its rudimentary