English forms. Our own Oarweed is sometimes found with a stem five feet long, ending in a flat frond four feet long and three wide; and Chorda filum, as we said before, grows to a length of thirty or forty feet. But what say you to a seaweed a quarter of a mile long? The stem of the Microcystis, a tropical seaweed, is said to attain the length of 1500 feet, forming a simple unbranched cord until it approaches the surface of the sea, when it forks repeatedly, each division bearing a single small leaf, and the whole forming a floating mass of foliage some hundreds of square yards in extent. We shall be better able to realise the enormous length of this plant if we remember that the largest forest tree with which we are acquainted, the Californian Wellingtonia, attains a height of not more than 450 feet.
The Nereocystis again, which is found on the western shores of America, though less gigantic than the Microcystis, is still of a tolerable size. The stem of this plant, though no thicker than whipcord, is upwards of 300 feet in length, and bears at its top a huge vesicle or hollow bag six or seven feet long, shaped like a barrel, and crowned with a tuft of fifty or sixty forked leaves, each from thirty to forty feet long. The stem of this plant is so strong that the natives often use if for a fishing line.
Less again than the Nereocystis, but not less quaintly shaped, is the Eklonia, the South African Trumpet-weed; so called because the native herdsmen use it as a trumpet for calling the cattle home in the evening. The stem of this plant is about twenty feet long, two inches in diameter at the base, and gradually widening upwards until it ends in a fan-shaped cluster of leaves each about twelve feet long.
And whilst we are speaking of tropical forms we must not forget to make mention of the “Praderias de Yerva,” the seaweed meadows of Columbus, vast fields of floating seaweed covering the surface of the sea for hundreds of square miles. One of these, Sargassos, as they are termed, is thus described by Lieutenant Maury in his “Physical Geography of the Sea:”—“Midway the Atlantic in the triangular space between the Azores, Canaries, and Cape de Verd Islands, is the great Sargasso sea. Covering an area equal in extent to the Mississippi valley, it is so thickly matted over with Gulf-weed that the speed of vessels passing through it is often much retarded. When the companions of Columbus saw it they thought it marked the limits of navigation, and became alarmed. To the eye at a little distance it seems substantial enough to walk upon. Patches of the weed are generally to be seen floating along the outer edge of the Gulf stream. The seaweed always tails to a steady or constant wind, and thus serves the mariner as a sort of marine anemometer, telling him whether the wind as he finds it has been blowing for some time, or whether it has just shifted, and which way. Columbus first found this weedy sea on his voyage of discovery. There it has remained until the present day, moving up and down and changing its position like the calms of Cancer, according to the season, the storms, and the winds. Exact observation as to its limits and their range, extending back for fifty years, assure us that its mean position has not altered since that time.”
The plants of which these vast floating meadows are composed belong for the most part to the species Sargassum bacciferum—the Berry-bearing Gulf-weed—which, unlike most other seaweeds, floats freely in the water, and is seldom or never found growing upon stones or rocks. This peculiarity is shared by at least one of our English seaweeds, Mackay’s Fucus, which inhabits salt marshes connected with the sea. The Gulf-weed is sometimes found upon our own shores, being conveyed there by the agency of the same currents by which West Indian fruits and seeds are occasionally thrown upon the western coasts of Ireland and Scotland. In appearance Gulf-weed closely resembles our own Bladder-wrack, differing chiefly in having the air-bladders from which the latter plant derives its common name, attached to short stalks instead of imbedded in the substance of the frond.
In all the great oceans, there exist two currents, one of warm water, running from the Equator to the Pole, and the other a return current of cold water, from the Pole to the Equator. In the quiet water between these two currents the Gulf stream has its home, and there we may expect to meet with Sargassos or seaweed seas. Thus, besides the Sargasso, sailed through by Columbus, which is bounded by the Gulf stream and the Equatorial current, there is another in the Pacific Ocean, whose banks are formed by the two currents, known respectively as Humboldt’s and the Black Current. There are now known and marked upon our charts at least five well-defined Sargassos, besides several smaller collections of seaweed. Of these latter the most remarkable instance is to be found in the Straits of Magellan, where the seaweed is often so thickly crowded as sensibly to impede the motion of the paddles of large steamers.
Of the three great classes into which the seaweeds are divided, the brown seaweeds are, with a few exceptions, the most highly organised. In them Nature gives the first hint of the division of the plant into root, stem, and leaf, of which she elsewhere makes so frequent use. The resemblance, however, of these seaweeds to more highly-organised plants, is merely external. The so-called root has neither the structure nor the functions of a true root, and the distinction between stem and leaf is one of external form only. Often, indeed, that which is now the stem has at an earlier period formed part of the leaf, just as in some of the red seaweeds the stem of this year’s plant was last year the midrib of the leaf-like frond.
The root of a seaweed serves no other purpose in the economy of the plant than that of attaching it to the stone or rock on which it grows. In many seaweeds it is merely an expansion of the stem into the form of a cone, the lower surface of which fits closely to the rock, and cleaves to it like the “sucker” with which schoolboys lift stones. In other plants, as in the common oarweed, the root is composed of a number of stout cords growing out of the frond, which twist round projections of the rock and insert themselves into
