10. The stately annual sun-flower displays this phenomenon more conspicuously, on account of its size: the flower follows the sun all day, and returns, after sunset, to the east, to meet his beams in the morning. A great number of leaves likewise follow the sun in its course. A clover field is a familiar instance of this. 11. The chemical actions of light, heat, and the component parts of the atmospheric air, upon leaves are now tolerably well understood. It is agreed that in the daytime plants imbibe, from the atmosphere, carbonic acid gas (which is a compound of oxygen and carbon), that they decompose it, absorb the carbon, as matter of nourishment, which is added to the sap, and emit the oxygen. 12. The burning of a candle, or the breathing of animals, in a confined space produces so much of this gas that neither of these operations can go on beyond a certain time; but the air so contaminated serves as food for vegetables, the leaves of which, assisted by light, soon restore the oxygen, or, in other words, purify the air again. This beautiful discovery shows a mutual dependence of the animal and vegetable kingdoms, and adds another to the many proofs we have of the wisdom and wonderworking power of the Creator of all things. 13. In the dark, plants give out carbonic acid, and absorb oxygen; but the proportion of the latter is small, compared to what they exhale by day, as must also be the proportion of carbonic acid given out; else the quantity of carbon added to their substance would be but trifling, especially in those climates in which the proportion of day to night is nearly equal, and which, notwithstanding, we know to be excessively luxuriant in vegetation. 14. There can be no question of the general purpose answered to the vegetable constitution by these functions of leaves. But when we attempt to consider how the peculiar secretions of different species and tribes of plants are formed; how the same soil, the same atmosphere, should, in a leaf of the vine or sorrel, produce a wholesome acid, and in that of others a most virulent poison; how sweet and nutritious herbage should grow among acrid crowfoot and aconite, we find ourselves totally unable to comprehend the existence of such wonderful powers in so small and, seemingly, simple an organ as the leaf of a plant. 15. The agency of the vital principle alone can account for these wonders, though it cannot, to our understandings, explain them. The thickest veil covers the whole of these processes; and so far have philosophers hitherto been from removing this veil, that they have not even been able to approach it. 16. All these operations, indeed, are evidently chemical decompositions and combinations; but we neither know what these decompositions and combinations are, nor the instruments in which they take place, nor the agents by which they are regulated. 1. Naturalized with us.-That is, so carefully cultivated that they adapt themselves to our climate. 2. Aquatic plants.-Plants that grow in water, as the water-lily. Sir J. E. Smith. 3. Chemical decomposition is the breaking up of bodies into their elements. For instance, the chemical decomposition of water produces the two gases, oxygen and hydrogen. LESSON XLV. FLOD DEN FIELD. Next morn the baron climbed the tower, Long Marmion looked; at length his eye Amid the shifting lines: The Scottish host drawn out appears, The eastern sunbeam shines. The Scots beheld the English host Leave Barmore-wood, their evening post, And heedful watched them as they crossed The Till by Twisel bridge. High sight it is, and haughty, while They dive into the deep defile; By rock, by oak, by hawthorn tree, Still pouring down the rocky den, And sweeping o'er the Gothic Arch, And why stands Scotland idly now, And sees, between him and his land, What vails the vain knight-errant's brand? O for one hour of Wallace wight, "But see! look up-on Flodden bent, |