They Were A Mixture Of Azotic Gas And Carbonic Acid.

Nitrous gas scarcely indicated the presence of oxygen.* (* In a hundred parts there were eighty-four of nitrogen, fifteen

Of carbonic acid gas that the water had not absorbed, and one of oxygen.) Lastly, I set the wood and the roots of the mangrove thoroughly wetted, to act on a given volume of atmospheric air in a phial with a ground-glass stopple. The whole of the oxygen disappeared; and, far from being superseded by carbonic acid, lime-water indicated only 0.02. There was even a diminution of the volume of air, more than correspondent with the oxygen absorbed. These slight experiments led me to conclude that it is the moistened bark and wood which act upon the atmosphere in the forests of mangrove-trees, and not the water strongly tinged with yellow, forming a distinct band along the coasts. In pursuing the different stages of the decomposition of the ligneous matter, I observed no appearance of a disengagement of sulphuretted hydrogen, to which many travellers attribute the smell perceived amidst mangroves. The decomposition of the earthy and alkaline sulphates, and their transition to the state of sulphurets, may no doubt favour this disengagement in many littoral and marine plants; for instance, in the fuci: but I am rather inclined to think that the rhizophora, the avicennia, and the conocarpus, augment the insalubrity of the air by the animal matter which they contain conjointly with tannin. These shrubs belong to the three natural families of the Lorantheae, the Combretaceae, and the Pyrenaceae, in which the astringent principle abounds; this principle accompanies gelatin, even in the bark of beech, alder, and nut-trees.

Moreover, a thick wood spreading over marshy grounds would diffuse noxious exhalations in the atmosphere, even though that wood were composed of trees possessing in themselves no deleterious properties. Wherever mangroves grow on the sea-shore, the beach is covered with infinite numbers of molluscs and insects. These animals love shade and faint light, and they find themselves sheltered from the shock of the waves amid the scaffolding of thick and intertwining roots, which rises like lattice-work above the surface of the waters. Shell-fish cling to this lattice; crabs nestle in the hollow trunks; and the seaweeds, drifted to the coast by the winds and tides, remain suspended on the branches which incline towards the earth. Thus, maritime forests, by the accumulation of a slimy mud between the roots of the trees, increase the extent of land. But whilst these forests gain on the sea, they do not enlarge their own dimensions; on the contrary, their progress is the cause of their destruction. Mangroves, and other plants with which they live constantly in society, perish in proportion as the ground dries and they are no longer bathed with salt water. Their old trunks, covered with shells, and half-buried in the sand, denote, after the lapse of ages, the path they have followed in their migrations, and the limits of the land which they have wrested from the ocean.

Enter page number Go  Previous Next
Page 305 of 407
Words from 158249 to 158762 of 211363