Page:The American Cyclopædia (1879) Volume II.djvu/91

 ATLANTIC OCEAN 79 corallines, so named from a family of seaweeds having their tissues filled with limer^and simu- lating small corals. As a general rule sea- wwds do not grow much deeper than 8 or 10 fathoms, though there are exceptions; thus the gigantic macrocystis pyrifera, found growing in 40 fathoms, and rising to the surface at an angle of 45, and streaming on it for a distance of several ships' lengths, has been estimated to have a total growth of 700 feet. Low forms of corallines have been found at more than 200 fathoms, and diatomacea at all explored depths. The geographical distribu- tion of seaweeds depends much on tem- perature and currents. The luminaries, for instance, prefer cold water, the sargasso, the warmest. The largest forms are found in colder water, as the laminarice in the north, the macrocystis, Lessonia, Durvillea, &c., in the south. As examples of the influence of cur- rents on the distribution, we may take padina pavoiiia, a West Indian species, not found in America N. of the Florida keys, but carried to the S. shore of England probably by the Gulf stream. The macrocystis and other large an- tarctic seaweeds luxuriate about Tierra del Fuego and the Falkland islands ; they are car- ried far toward the equator by the Peruvian current on the W. coast of South America, while they are kept back on the E. coast by the southerly extension of the Brazilian cur- rent. A very remarkable feature of ocean vegetation is the Sargasso sea. This name is commonly used to designate a region of the Atlantic covered by a peculiar floating sea- weed, either in tangled masses of considerable extent, compared by some writers to floating prairies or submerged meadows, or simply in scattered sprigs. Columbus, as is well known, passed through these fields of seaweed in his first voyage, to the great alarm of his com- panions, who from previous association would naturally imagine a connection between sea- weeds and rocks or shoals. Since that time, for nearly four centuries, observation has shown that the geographical position and the abun- dance of these plants remain essentially un- changed. Ilumboldt found that the gulf weed, as it is generally called, because found also in the Gulf stream, was distributed in two principal masses, the largest situated a little to the west of the meridian of Fayal and between the parallels of 25 and 36 N. North- west winds are said to carry it sometimes to the latitudes 24 to 20. The second or lesser bank is less known, according to the same author, and occupies a space between the Ba- hamas and Bermudas. Capt. Leps of the French navy has investigated the subject more recently, and places the principal bank between Ion. 29 and 45 W., and lat. 21 and 33 N., with smaller scattered masses extending several degrees beyond these limits on all sides. The smaller bank he found not so well defined, the denser portion forming a band ex- tending to the N. E. of Porto Rico and to the 58 VOL. ii. 6 latitude of Bermuda. The Sargasso sea corre- sponds to the great centre or eddy of the North Atlantic system of currents, of which the Gulf stream forms so important a part. The botani- cal name of the gulf weed is sarga&sum bacci- ferum (Agardh), not sargassum natans, as it is usually called in books of navigation, which is a species growing on rocks in the West Indies. It is generally found in sprigs a few inches long, with a main stem branching into secon- dary ones ; the main stem has frequently a de- caying end, while the other gives rise to fresh- growing leaves ; but there is never any trace of root or place of attachment. Between the leaves, which are elongated and sharply ser- rate, small round air vessels, the size of currants, are supported on short peduncles. These air vessels or floats are vulgarly taken for the seeds or fruits ; hence the name, de- rived from a Portuguese word meaning grapes, and the French names of raisins de mer and raisins du tropique (sea grapes and tropic grapes). Far from being seeds, it is a sin- gular fact that the plant has never been ob- served to produce a fructification, and that it propagates only by division. Prof. Agassiz has observed that deprived of its floats the plant sinks. Humboldt, in his personal narrative, thought it might possibly grow on an undis- covered bank of 40 or 60 fathoms depth. This opinion he afterward abandoned ; but as it is still current among some persons, it may be stated here that such a bank in mid-ocean would have revealed itself by discoloration of the water before now, and to produce the im- mense masses of floating weed would have to be of considerable size ; besides, soundings in different parts of the Sargasso sea have re- vealed a very great depth of the ocean in that part. It is furthermore well known that fu- coids grow only in very moderate depths, the greater number of species being confined be- tween tide marks. Humboldt in later works adopted the more probable supposition that the gulf weed originates and propagates where it is found. To this he was led by the ob- servations of Meyen, who examined several thousand specimens during a voyage across the Sargasso sea, and found them uniformly desti- tute of roots or fructifications. Robert Brown, however, thought the question of origin still obscure, but that the theory of propagation by ramification and division was highly probable. He thought it possible that it might have origi- nated from some nearly allied species in the gulf of Florida, fucus natans for instance, afterward permanently modified by the cir- cumstances in which it had been placed for ages. Harvey, a high authority in the knowl- edge of seaweeds, who explored the shores of Florida and examined the fresh gulf weed, is also clearly of the opinion that it propagates only by division, whatever may have been the origin of the species. The gulf weed harbors a peculiar fauna consisting of fishes, Crustacea, mollusks, and polyps. Among the fishes, a