Page:The Botany of the Antarctic Voyage.djvu/501

Falklands, etc.] when the prospect of solving them is gone by; and when they but add to the thousand regrets over lost opportunities, the remembrance of which weighs so heavily on the mind of every naturalist, that the brightest prospects of discovery in the fair future can never obliterate them.

So many interesting points are connected with the Macrocystis, that a book might be instructively filled with its history, anatomy, physiology and distribution; whilst its economy, its relation to other vegetables and to the myriads of living creatures which depend on it for food, attachment, shelter and means of transport, constitute so extensive a field of research that the mind of a philosopher might shrink from the task of describing them. We conclude with an outline of its dispersion over the surface of the globe, which is wider than that of any of the large Algæ.

As already mentioned, the Macrocystis girds the globe in the Southern temperate zone, but not in the Tropics or Northern Hemisphere, and this is a most curious trait in its history. We may first, however, trace the southern edge of the belt which it forms, and we are the better enabled to do so, because the limits of its existence, as a floating plant, were observed in six different longitudes in the passage of the Antarctic Expedition as often between the Southern Sea and the Southern Ice, within which there is no vegetation. The southern boundary of the "Macrocystis sea" is very much determined by the position of the ice, and the northern by the currents and temperature of the water. Thus, in the longitude of New Zealand, where open sea extends to the 65th degree, this plant is found as far as 64°, the specimens having probably been drifted originally from Kerguelen's Land or the Crozets, which are the great nurseries for it in the Eastern Hemisphere, and from whence all those drifting islets have been wafted which occur between their longitude and Cape Horn. In the longitude of Cape Horn, 58° or 60° is the highest parallel it attains, for it has not been found amongst the South Shetlands ; further east, in the South Atlantic, its parallel is probably still lower ; till in the meridian of the Cape of Good Hope it is 40 degrees removed from the Pole, being seen no further south than 50° 30'. There the Atlantic Ocean specimens are derived from the southern extreme of America and the neighbouring islands. Its northern range on the other hand is dependent, 1st, on the temperature of the ocean;—for it neither enters the Tropics of the Atlantic, nor passes up the shores of Africa or into the Indian Ocean ; whilst it does inhabit the whole surface of the Pacific Ocean and the west coast of both Americas: 2ndly, on the currents, for when north of the influence of the uniform westerly movement of the waters in the Antarctic Ocean, it is deflected with their courses and carried, while temperature allows, to whatever seas receive those waters. Thus, the South Polar current divides at Cape Horn, one portion following the west coast of South America to Cape Blanco and the Galapagos Islands under the Equator, carrying the Macrocystis with it, which then enters the cold waters which flow from the Arctic Islands of the Pacific, and over whose entire surface it is spread, reaching Kamtschatka, New California, and the Aleutian Islands : so that in the longitude of Western America the Macrocystis ranges from the Arctic to the Antarctic circle. The eastern branch of the Cape Horn current passes between the Falkland Islands and Fuegia, conveying vast masses of this sea-weed 200 miles north of the Falklands, as low as the 44th degree, and some even reaching the Plate river in 35°, its northern limits in the Western Atlantic. Further west in the Antarctic ocean its distribution is less known; but since it does not occur far north of the Cape of Good Hope in that meridian, we may conclude that it ceases about the 34th degree. With regard to the South African habitat, it is difficult to account for so vast a quantity as the Ao-ulhas Bank exhibits, for these waters, 130 miles in breadth, flowing with a rapid stream from the N.E. or Indian Ocean, literally swarm with Macrocystis, which possibly is taken up from the northern edge of the westerly Polar current (which flows along the parallel of 45° S.) by the Indian (or N. E.) current in question.

Its northern limit in the Indian Ocean is not ascertained, but it lies probably south of a line drawn northeast from the Cape of Good Hope to Australia, upon whose western shores the plant is found, as also in New Zealand, and on the coast of China to the north, to which sea it perhaps migrates from the North Pacific Ocean, Kamtschatka, &c.

CLXIX., CLXX. Frond of M. pyrifera, var. luxurians, of the natural size; 1, thin slice of fructifying