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Show MARINE VEGETATION. [Ch. V. Lamouroux that it is divisible into different systems, apparently as d1. st.m ct as' those on the 1a n d , no t WI't l1 s tanding that the uni. formity of temperature is so much greater in the ocean. For on that ground we might have expected the phenomenon of partial distribution to have been far less stri~ing, sine~ clim~te is, in general, so influential a cause in checkmg the dispersiOn of species from one zoue to another. . The number of hydrophytes, as they are termed, Is very considerable, and their stations are found to be infinitely more varied than could have been anticipated; for while some plants are covered and uncovered daily. by the tide, others live in abysses of the ocean, at the extraordinary depth of one thousand .feet; and although in such situations there must reign darkness more profound than night, at least to our organs, many of these vegetables are highly coloured. From the analogy of terrestrial plants we should have inferred that the colouring of the algre was derived from the influence of the solar rays; yet we are compelled to doubt when we reflect how feeble must be the rays which penetrate to these great depths. The subaqueous vegetation of the Mediterranean is, upon the whole, distinct from that of the Atlantic on the west, and that part of the .Arabian gulf which is immediately con· tiguous on the south. Other botanical provinces are found in the West-Indian seas, including the gulf of Mexico; in the ocean which washes the shores of South America, in the Indian ocean and its gulfs, in the seas of Australia, and in the Atlantic basin, from the 40° of north lat. to the pole. There are very few species common to the coast of Europe and the United States of North America, and none common to the Straits of Magellan and the shores of Van Diemen's Land. It must not be overlooked, that the distinctness alluded to between the vegetation of these several countries relates strictly to species and not to forms. In regard to the numerical pre· ponderance of certain forms, and many peculiarities of internal structure, there is_ a marked agreement in the vegetable pro• Ch. V.J DISPJ<~RSION OF SEEDS. 73 ductions of districts placed in corresponding latitudes, and under similar physical circumstances~ however re·mote their position. Thus there are innumerable points of analogy between the vegetation of the Brazils, equinoctial Africa, and India; and there are also points of difference wherein the plants of these regions are distinguishable from all extra-tropical groups. But there are very few species common to the three continents. The same may be said, if we compare the plants of the Straits of Magellan with those of Van Diemen's Land, or the vegetation of the United States with that of the middle of Europe: the species are distinct, but the forms are in a great degree analogous. Let us now consider what means of diffusion, independently of the agency of man, are possessed by plants, whereby, in the course of ages, they may be enabled to stray from one of the botanical provinces above mentioned to another, and to establish new colonies at a great distance from their birth-place. The principal of the inanimate agents, provided by nature for scattering the seeds of plants over the globe, are the movements of the atmosphere and of the ocean, and the constant flow of water from the mountains to the sea. 'To begin with the winds: a great number of seeds are furnished with downy and feathery appendages, enabling them, when ripe, to float in the air, and to be wafted easily to great distances by tl1e most gentle breeze. Other plants are fitted for dispersion by means of an attached wing, as in the case of the fir-tree, so that they are caught up by the wind as they fall from the cone, and are carried to a distance. Amongst the comparatively small number of plants known to Linnreus, no less than one hundred and thirty-eight genera are enumerated as }1aving winged seeds. As winds often prevail for days, weeks, or even months together, in the same direction, these means of transportation may sometimes be without limits ; and even the heavier grains may be borne through considerable spaces, in a very short time, during ordinary tempests; for strong gales, which can |