Marine vegetation varies both horizontally and vertically with the depth, and it seems to be a general law throughout the ocean, that the light of the sun and vegetation cease together. It consequently depends upon the power of the sun, and the transparency of the water; so that different kinds of sea weeds affect different depths, where the weight of the water, and the quantity of light and heat, suit them best. One great marine zone lies between high and low water marks, and varies in species with the nature of the coasts, but exhibits similar phænomena throughout the northern hemisphere. In the British seas this zone does not extend deeper than thirty fathoms, but it is divided into two distinct provinces, one to the south and another to the north. The former includes the southern and eastern coasts of England, the southern and western coasts of Ireland, and both the Channels; while the northern flora is confined to the Scottish seas, and the adjacent coasts of England and Ireland. The second British zone begins at low water mark, and extends below it to a depth of from seven to fifteen fathoms. It contains the great tangle sea weeds or marine forests mixed with fuci, and is the abode of a host of animals. A coral-like sea weed is the last plant of this zone and the lowest in these seas, where it does not extend below the depth of sixty fathoms; but in the Mediterranean it is found at seventy or eighty fathoms, and is the lowest plant in that sea. The same law prevails in the Bay of Biscay, where one set of sea weeds is never found lower than twenty feet below the surface, another only in the zone between five and thirty feet, another between fifteen and thirty-five feet. In these two last zones they are most numerous; at a greater depth the kinds continue to vary, but their numbers decrease. The distribution in the Ægean sea was found by Professor E. Forbes to be perfectly similar, only that the vegetation is different and extends to a greater depth in the Mediterranean than in more northern seas. He also observed that sea weeds growing near the surface are more limited in their distribution than those that grow lower down, and that with regard to vegetation, depth corresponds with latitude, as height does on land. Thus the flora at great depths in warm seas is represented by kindred forms in higher latitudes. There is every reason to believe that the same laws of distribution prevail not only throughout the ocean, but in every sea. SECTION III. FUNGI.