Page:The Botany of the Antarctic Voyage.djvu/500

464 elongation of the upper part of a plant which never branches, and whose growth is independent of all below it, even of the root. Specimens measuring between 100 and 200 feet are common in the open ocean, and these are always broken off at the lower end, either from the division of the frond by sea-animals, through whose agency the plant increases and the floating island it forms dilates, or from the impossibility of securing the whole mass from the motion of the vessel or the swell of the sea, in latitudes where no boat can be lowered. Again, D'Urville, upon whose observations in natural history the utmost reliance may be placed, states it to grow in eight, ten and even fifteen brasses of water, from which depth it ascends obliquely and floats along the surface nearly as far: this gives a length of 200 feet. In the Falkland Islands, Cape Horn and Kerguelen's Land, where all the harbours are so belted with its masses that a boat can hardly be forced through, it generally rises from eight to twelve fathom water, and the fronds extend upwards of one hundred feet upon the surface. We seldom, however, had opportunities of measuring the largest specimens, though washed up entire on the shore; for on the outer coasts of the Falkland Islands, where the beach is lined for miles with entangled cables of Macrocystis, much thicker than the human body, and twined of innumerable strands of stems coiled together by the rolling action of the surf, no one succeeded in unravelling from the mass any one piece upwards of seventy or eighty feet long ; as well might we attempt to ascertain the length of hemp fibre by unlaying a cable. In Kerguelen's Land, the length of some pieces, which grew in the middle of Christmas Harbour, was estimated at more than three hundred feet ; but by far the largest seen during the Antarctic Expedition, were amongst the first of any extraordinary length which the ships encountered, and they were not particularly noticed, from the belief that the report of upwards of 1000 feet length was true; or, at any rate, that better opportunities of testing its truth would arise in the course of a three years' voyage, than the first week of our explorations could afford. These occurred in a strait between two of the Crozet Islands, where, very far from either shore, in what is believed to be forty fathoms water, somewhat isolated stems of Macrocystis rose at an angle of 45° from the bottom, and streamed along the surface for a distance certainly equal to several times the length of the ' Erebus '; — data, which if correct, (and we believe them so) give the total length of the stems as about 700 feet.

That isolated patches of weed should rise through such a volume of water is not incompatible with the statements we have elsewhere made, that eight or ten fathoms is the utmost depth at which, judging by our experience, submerged sea-weed vegetates in the Southern temperate and Antarctic Ocean. These exceptional cases are probably due to the parent plant having attained such a size in its birth-place near shore, as to weigh its stony moorings and deposit itself in deeper water, where an increase of the roots would unite the original base to other rocks, and thus gain a footing that defies the power of the elements.

We have stated that the elongation of the Macrocystis may be indefinite; but this is only true partially and in the case of detached patches: for the stem of the attached plant does not gain bulk or tenacity, after a certain period ; whilst the growing dimensions of the floating portion are increasing the difference between the specific gravity of the vegetable and the element it inhabits, and consequently augmenting the strain upon the slender stem by which it is attached. At some period or other, the resistance is overcome and the floating part detached from the submerged : though at what epoch this may take place, or whether it be coincident with other phases in the life of the plant, is beyond our conjecture.

The fact that fructification is produced only on the submerged young bladderless and small frond, within a few inches of the very root, is highly remarkable. What then is the function of the floating mass of the plant? to one of whose thousand leaves, each four to six feet long, the fructifying part bears an inconceivably small proportion. Were this a phaenogamic plant, we should recognize, in such foliaceous expansions, organs which fulfil a respiratory and digestive office and are subservient and necessary to the development of the more important parts of the vegetable ; but in this case such a mutual dependency is not so easily traced. As in Lessonia the multiplication of the leaves is intimately connected with the development in diameter of the stem, so in Macrocystis the development of fructifying fronds may take place only at the root of the barren ones, on whose previous existence they may be dependent for their origin. These are, however, questions which propose themselves to us in the closet only,