The largest of indigenous sea-weeds are the Laminaria saccharina and digitata, or the sugary and fingered oar-weeds. Their stout woody stems, and broad tough glossy leaves of dark olive-green, often twelve or fourteen feet long, must be familiar to every one who has sojourned on the coast. When gliding over their submerged groves in a boat, their great fronds floating like streamers in the water afford the interesting spectacle of a dense submarine thicket, through whose palm-like tops the fishes swim in and out, emulating in activity the birds of our forests.

But our native oar-weeds, large as they seem with regard to the other fuci among which they grow, are mere pygmies when compared with the gigantic species which occur in the colder seas.

None of the members of this family grow in the tropical waters, but they extend to the utmost polar limits, and seem to increase in size and multiplicity of form as they advance to the higher latitudes. The northern hemisphere has generally different genera from the southern. To the former belong the gigantic Alarias with their often forty feet long and several feet broad fronds, the singularly perforated Thalassophyta, and the far-spreading Nereocystis, which is only found in the Northern Pacific; while the genera Macrocystis and Lessonia are denizens of the Southern Ocean.

In the numerous channels and bays of Tierra del Fuego, the enormous and singular Macrocystis pyrifera is found in such incredible masses as to excite the astonishment of every traveller. "On every rock," says Mr. Darwin, perhaps the best observer of nature that ever visited those dreary regions, and certainly their most poetical describer, "the plant grows from low-water mark to a great depth, both on the outer coast and within the channels. I believe, during the voyages of the Adventure and Beagle, not one rock near the surface was discovered which was not buoyed by this floating weed. The good service it thus affords to vessels navigating near this stormy land is evident, and it certainly has saved many a one from being wrecked. I know few things more surprising than to see this plant growing and flourishing amidst those great breakers of the western ocean, which no mass of rock, let it be ever so hard, can long resist. The stem is round, slimy, and smooth, and seldom has a diameter of so much as an inch. A few taken together are sufficiently strong to support the weight of the large loose stones to which in the inland channels they grow attached; and some of these stones are so heavy, that when drawn to the surface they can scarcely be lifted into a boat by one person."

"Captain Cook, in his second voyage says, that 'at Kerguelen's Land some of this weed is of most enormous length, though the stem is not much thicker than a man's thumb. I have mentioned that, on some of these shoals on which it grows, we did not strike ground with a line of twenty-four fathoms; the depth of water, therefore, must have been greater. And as this weed does not grow in a perpendicular direction, but makes a very acute angle with the bottom, and much of it afterwards spreads many fathoms on the surface of the sea, I am well warranted to say that some of it grows to the length of sixty fathoms and upwards.'

"Certainly at the Falkland Islands, and about Tierra del Fuego, extensive beds frequently spring up from ten and fifteen fathoms water. I do not suppose the stem of any other plant attains so great a length as 360 feet, as stated by Captain Cook. Its geographical range is very considerable; it is found from the extreme southern islets near Cape Horn, as far north on the eastern coast as lat. 43°, and on the western it was tolerably abundant, but far from luxuriant, at Chiloe, in lat. 42°. It may possibly extend a little further northward, but is soon succeeded by a different species.

"We thus have a range of 15° in latitude, and as Cook, who must have been well acquainted with the species, found it at Kerguelen's Land, no less than 140° in longitude.

"The number of living creatures, of all orders, whose existence intimately depends on the kelp, is wonderful. A large volume might be written, describing the inhabitants of one of these beds of sea-weed. Almost every leaf, except those that float on the surface, is so thickly incrusted with corallines as to be of a white colour. We find exquisitely delicate structures, some inhabited by simple hydra-like polypi, others by more organised kinds and beautiful compound ascidiÆ. On the flat surfaces of the leaves, various patelliform shells, trochi, uncovered mollusks, and some bivalves are attached. Innumerable crustacea frequent every part of the plant. On shaking the great entangled roots, a pile of small fish, shells, cuttle-fish, crabs of all orders, sea-eggs, star-fish, beautiful holothuriÆ (some taking the external form of the nudibranch mollusks), planariÆ, and crawling nereidous animals of a multitude of forms, all fall out together. Often as I recurred to a branch of the kelp, I never failed to discover animals of new and curious structure. In Chiloe, where, as I have said, the kelp did not thrive very well, the numerous shells, corallines, and Crustacea were absent, but there yet remained a few of the FlustraceÆ, and some compound ascidiÆ; the latter, however, were of different species from those in Tierra del Fuego. We here see the fucus possessing a wider range than the animals which use it as an abode.

"I can only compare these great aquatic forests of the southern hemisphere with the terrestrial ones in the intertropical regions. Yet, if the latter should be destroyed in any country, I do not believe nearly so many species of animals would perish, as under similar circumstances would happen with the kelp. Amidst the leaves of this plant numerous species of fish live, which nowhere else would find food or shelter; with their destruction the many cormorants, divers, and other fishing-birds, the otters, seals, and porpoises, would soon perish also; and lastly the Fuegian savage, the miserable lord of this miserable land, would redouble his cannibal feast, decrease in numbers, and perhaps cease to exist."

For many a day's sail before reaching Cape Horn, large bundles of the macrocystis detached by the storm announce to the navigator that he is approaching the desolate coasts of Tierra del Fuego.

"We succeeded," says Professor Meyen, in his Reise um die Welt, "in getting hold of one of these floating islands, which, amid loud acclamations, was hauled upon deck by the exertions of five men. It was quite impossible to disentangle the enormous mass; we could only detach, to the length of about sixty feet, what we considered to be the chief stem; the branches were from thirty to forty feet long, and as thick as the principal trunk from which they sprang. We estimated the total length of the plant at about two hundred feet; the pear-shaped air vessels at the basis of the leaves were often six or seven inches long, and the leaves themselves measured seven or eight feet. On these swimming fucus-islands lived a vast multitude of various animals; thousands upon thousands of barnacles and sertulariÆ, of crustaceans and annelides.

"The admiration which the gigantic sea-weeds of Tierra del Fuego excited in our minds equalled that which had been raised by the exuberant vegetation of the virgin forests of Brazil. One single plant of the Macrocystis pyrifera would suffice, like one of the mammoth-trees of those luxuriant woods, to cover a large space of land with its leaf-like substance. The quantity of small algÆ, of sertularias, cellarias, and other minute animals dwelling on these swimming islands, surpasses in variety the multitude of parasitical plants bedecking the trees in a tropical forest. It seems as if, in these desolate and dreary regions, the generative powers of the planet were solely confined to the gigantic growth of submarine vegetation."

On the rocky coasts of the Falkland Islands are found no less astonishing masses of enormous sea-weeds, chiefly belonging to the genera Macrocystis, Lessonia, and Durvillea. Rent from the rocks to which they were attached, and cast ashore, they are rolled by the heavy surf into prodigious vegetable cables, much thicker than a man's body and several hundred feet long. Many of the rarest and most beautiful algÆ may be here discovered, which have either been wrenched from inaccessible rocks far out at sea, along with the larger species, or have attached themselves parasitically to their stems and fronds. Many of them remind the botanist, by some similarity of form, of the sea-weeds of his distant home, while others tell him at once that he is far away in another hemisphere. The gigantic lessonias particularly abound about these islands. Their growth resembles that of a tree. The stem attains a height of from eight to ten feet, the thickness of a man's thigh, and terminates in a crown of leaves two or three feet long, and drooping like the branches of a weeping-willow. They form large submerged forests, and, like the thickets of the macrocystis, afford a refuge and a dwelling to countless sea animals.

A similar abundance of colossal algÆ is found in the Northern Pacific, about the Kurile and Aleutic Islands, and along the deeply indented and channel-furrowed north-west coast of America.

Thus the Nereocystis lutkeana forms dense forests in Norfolk Bay and all about Sitcha. Its stem, resembling whipcord, and often above 300 feet long, terminates in a large air-vessel, six or seven feet long, and crowned with a bunch of dichotomous leaves, each thirty or forty feet in length. Dr. Mertens assures us that the sea-otter, when fishing, loves to rest upon the colossal air-vessels of this giant among the sea-weeds, while the long tenacious stems furnish the rude fishermen of the coast with excellent tackle. The growth of the nereocystis must be uncommonly rapid, as it is an annual plant, and consequently develops its whole gigantic proportions during the course of one brief summer.

Before proceeding to the third chief group of marine plants, the red sea-weeds, or Rhodosperms, I must mention the enormous fucus banks, or floating meadows of the Atlantic, which form undoubtedly one of the greatest wonders of the ocean.

We know that the mighty Gulf Stream, which rolls its indigo-blue floods from America to the opposite coasts of the Old World, flows partly southwards in the neighbourhood of Azores, and is ultimately driven back again to America. In the midst of these circuitous streams, from 22° to 36° N. lat., and from 35° to 65° W. long., extends a sea without any other currents than those resulting from the temporary action of the winds. This comparatively tranquil part of the ocean, the surface of which surpasses at least twenty times that of the British Isles, is found more or less densely covered with floating masses of Sargassum bacciferum. Often the sea-weed surrounds the ship sailing through these savannas of the sea, in such quantities as to retard its progress, and then again hours may pass when not a single fucus appears. While Columbus was boldly steering through the hitherto unknown fields of the Sargasso Sea, the fears of his timorous associates were increased by this singular phenomenon, as they believed they had now reached the bounds of the navigable ocean, and must inevitably strike against some hidden rock, if their commander persevered in his audacious course.

It is an interesting fact that the Sargasso Sea affords the most remarkable example of an aggregation of plants belonging to one single species. Nowhere else, according to Humboldt, neither in the savannas of America, nor on the heaths or in the pine forests of Northern Europe, is such a uniformity of vegetation found as in those boundless maritime meadows.

"The masses of sea-weeds," says Meyen, "covering so vast an extent of ocean have ever since the time of Columbus been the object of astonishment and inquiry. Some navigators believe, that they are driven together by the Gulf Stream, and that the same species of Sargassum plentifully occurs in the Mexican Sea; this is however perfectly erroneous.

"Humboldt was of opinion that this marine plant originally grows on submarine banks, from which it is torn by various forces; I for my part have examined many thousands of specimens, and venture to affirm that they never have been attached to any solid body. Freely floating in the water, they have developed their young germs, and sent forth on all sides roots and leaves, both of the same nature."

Thus the Sargassum seems to be the indigenous production of the sea where it appears, and to have floated there from time immemorial. Its swimming islands afford an abode and nourishment to a prodigious amount of animal life. They are generally covered with elegant sertularias, coloured vorticellas, and other strange forms of marine existence. Various naked or nudibranchiate mollusks and annelides attach themselves to the fronds, and afford nourishment to hosts of fishes and crustaceans, the beasts of prey of this little world.

Similar aggregations of sea-weeds are also met with in the Indian and Pacific Oceans, in the comparatively tranquil spaces encircled by rotatory currents. Their rare occurrence on the surface of the sea may serve as a proof of the restless motion of its waters. Were the ocean not everywhere intersected by currents, it would most likely be covered with sea-weeds, opposing serious, if not invincible obstacles to navigation.

The Red sea-weeds, Rhodosperms or FlorideÆ, are by far the most numerous in species, and undoubtedly the most beautiful and perfect of all the algÆ. They love neither light nor motion, and generally seek the shade of larger plants on the perpendicular sides of deep tide-pools removed from the influences of the tides and gales. They mostly grow close to low-water mark, and are to be seen only for an hour or two at the spring-tides, during which, as is well known, the deepest ebbs take place. To this group belong the wonderfully delicate polysiphonias, callithamnias, plocamias, and delesserias, whose elegant rosy scarlet or purple leaves are the amateur's delight, and when laid out on paper resemble the finest tracery, defying the painter's art to do justice to their beauty. It likewise numbers among its genera the chalky corallines and nullipores, which on account of the hardness of their substance were formerly considered to be polyps, but whose true nature becomes apparent on examining their internal structure.

The Chondrus crispus, or Carrigeen, which grows in such vast quantities on the coasts of the British Isles, also belongs to the rhodosperms, though when growing, as it frequently does, in shallow tide-pools, exposed to full sunlight, its dark purple colour fades into green or even yellowish white. When boiled it almost entirely dissolves in the water, and forms on cooling a colourless and almost tasteless jelly, which of late years has been largely used in medicine as a substitute for Iceland moss. Similar nutritious gelatines, which also serve for the manufacture of strong glues, are yielded by other species of rhodosperms, among others by the Gracillaria spinosa of the Indian Ocean, which the Salangana (Hirundo esculenta), a bird allied to the swallow, is said principally to use for the construction of her edible nest.

The steep sea-walls along the south coast of Java are clothed to the very brink with luxuriant woods, and screw-pines strike everywhere their roots into their precipitous sides, or look down by thousands from the margin of the rock upon the unruly sea below. The surf of incalculable years has worn deep caves into the chalk cliffs, and here the Salangana builds her nest. Where the sea is most agitated whole swarms are observed flying about, and purposely seeking the thickest wave-foam. From a projecting cape, on looking down upon the play of waters, may be seen the mouth of the cave of Gua Rongkop, sometimes completely hidden under the waves, and then again opening its black recesses, into which the swallows vanish, or from which they dart forth with the rapidity of lightning. While at some distance from the coast the blue ocean sleeps in undisturbed repose, it never ceases to fret and foam against the foot of the mural rocks, where the most beautiful rainbows glisten in the eternally rising vapours.

Who can explain the instinct which prompts the birds to glue their nests to the high dark vaults of those deep, and apparently so inaccessible, caverns? Did they expect to find them a safe retreat from the persecutions of man? Then surely their hopes were vain, for where is the refuge to which his insatiable avidity cannot find the way? At the cavern of Gua-gede, the brink of the precipitous coast lies eighty feet above the level of the sea at ebb-tide; the wall first bends inwards, and then, at a height of twenty-five feet from the sea, throws out a projecting ledge which is of great use to the nest-gatherers, serving as a support for a rotang ladder let down from the cliff. The roof of the cavern's mouth lies only ten feet above the sea, which, even at ebb-tide, completely covers the floor of the cave, while at flood-tide the opening of the vast marine grotto is entirely closed by every wave that rolls against it. To penetrate into the interior is thus only possible at low water, and during very tranquil weather; and even then it could not be done, if the rugged roof were not perforated and jagged in every direction. The boldest and strongest of the nest-gatherers wedges himself firmly in the hollows, or clings to the projecting stones, while he fastens rotang ropes to them, which then depend four or five feet from the roof. To the lower ends of these ropes long rotang cables are attached, so that the whole forms a kind of suspension bridge throughout the entire length of the cavern, alternately falling and rising with its inequalities. The cave is 100 feet broad and 150 long as far as its deepest recesses. If we justly admire the intrepidity of the St. Kildans, who, let down by a rope from the high level of their rocky birthplace, remain suspended over a boisterous sea, we must needs also pay a tribute of praise to the boldness of the Javanese nest-gatherers. Before preparing their ladders for the plucking of the birds' nests, they first offer solemn prayers to the goddess of the south-coast, and sometimes deposit gifts on the tomb where the first discoverer of the caverns and their treasures is said to repose. Thus in all zones and in every stage of civilisation, man is directed by an inward voice to seek the protection of the invisible powers when about to engage in a great and perilous undertaking.

As I have already mentioned, the Salangana builds her nest of sea-weeds, which she softens in her stomach and then disgorges. During its construction new layers, which soon grow hard in the air, are continually deposited on the margin, until it has attained the proper size. When gathering time approaches, some of the pluckers daily visit the cavern to examine the state of the brood. As soon as they find that most of the young are beginning to be provided with feathers, their operations commence. These nests form the first quality; those in which the young are still completely naked, the second; while those which only contain eggs, and are consequently not yet ripe, rank third. The nests with young whose feathers are completely developed are over-ripe, black, and good for nothing. All the young and eggs are thrown into the sea. The gathering takes place three times a year; the birds breed four times a year. In spite of these wholesale devastations their numbers do not diminish; as many of the young have no doubt flown away before the day of execution, or other swallows from still unexplored caverns may fill up the void. In this manner about 50 piculs are annually collected, which the Chinese pay for at the rate of 4000 or 5000 guilders the picul. Each picul contains on an average 10,000 nests. Dividing these 500,000 nests among three gatherings, and reckoning two birds to each nest, we find that more than 333,000 swallows inhabit at the same time the Javanese coast caverns.

In the interior of the island, in the chalkstone grottos of Bandong, the Salangana also breeds, but in far inferior numbers, as here the annual collection amounts on an average to no more than 14,000 nests. In these inland caves swallows and bats reside together, but without disturbing each other, as the former when not breeding leave their caverns at sunrise, disappear in the distance, and only return late in the evening, when the bats are already enjoying their vespertine or nocturnal flight.

In Sumatra and some other islands of the Indian archipelago, birds'-nests are likewise collected, but nowhere in such numbers as in Java. They are brought to the Chinese market, where they are carefully cleaned before being offered for sale to the consumer. The addition of costly spices renders them one of the greatest delicacies of Chinese cookery, but as for themselves they are nothing better than a fine sort of gelatine.

The Japanese have long been aware that these costly birds' nests are in fact merely softened algÆ. They consequently pulverise the proper species of sea-weeds, which are abundantly found on their own coasts, boil them to a thick jelly, and bring them to market under the name of Dschin-schan, as artificial birds'-nests. The Dutch call it Agar-agar, and make great use of it; simple boiling sufficing to convert the dried substance into a thick uniform jelly, which is both nourishing and easy of digestion. Thus we see that the algÆ, which the Romans considered so perfectly worthless that, when they wished to express their utter contempt of an object, they declared it to be still viler than the vile sea-weed, are by no means deserving of so hard a sentence. Man himself might be much more justly reproached for neglecting the abundant stores of nourishment which nature has gratuitously provided for him on all flat and rocky coasts. For not only the species I have mentioned are eatable, but also some of the commonest fuci of our seas (Fucus nodosus, F. vesiculosus, Laminaria saccharina), as well as the gigantic alarias and durvilleas of the colder oceanic regions. And yet how rare is their use, notwithstanding the increasing wants of a rapidly growing population!

Besides the larger forms of vegetation, the ocean contains a vast number of microscopical plants. Among these the most remarkable are the DiatomaceÆ, simple vegetable cells enclosed in a flinty envelope, consisting of two plates closely applied to each other like the two valves of a mussel. The forms of these minute organisms are no less curious than those of the Foraminifera, for they exhibit regular mathematical figures, and their surface is often most delicately sculptured. Multiplying by spontaneous fissure, many of the Diatoms are met with entirely free after the process of duplicative subdivision has once been completed, while others, such as the Licmophora, or Fan-bearer, an elegant native species, habitually remain coherent one to another, producing clusters or filaments of various shapes, connected by a gelatinous investment or by a stalk-like appendage, which serves to attach them to other plants or to stones and to pieces of wood. Though individually invisible to the naked eye, they appear, when thus congregated, as patches of a green or brownish slimy mass, or as little glittering tufts a line or two in height. Some of their numerous species are natives of fresh water, but by far the majority are denizens of the sea, where they are found from the equator to the poles. The brown scum floating upon the surface of the antarctic waters near the mighty ice barrier which arrested Sir James Ross's progress to the south pole was found to consist almost solely of DiatomaceÆ, and they are equally abundant in the Arctic Ocean.

It is remarked by Dr. Hooker that the universal presence of this invisible vegetation throughout the South Polar Seas is a most important feature, since there is a marked deficiency in this region of higher forms of vegetation, so that without the Diatoms there would neither be food for aquatic animals nor (if it were possible for these to maintain themselves by preying on one another) could the ocean waters be purified of the carbonic acid which animal respiration would be continually imparting to it. Thus it is not in vain that they abound in the most inhospitable seas, where but for them no sea-bird would flap its wings, and no dolphin dart through the desert waters.

From the indestructible nature of their flinty coverings the Diatoms play a no less conspicuous part in the geological history of our globe than the calcareous Foraminifera.

Extensive rocky strata, chains of hills, beds of marl—once deposited at the bottom of the ocean, and raised by subsequent changes of level from the depth of the waters—contain the remains of these little plants in greater or less abundance. No country is destitute of such monuments, and in some they constitute the leading features in the structure of the soil. Under the whole city of Richmond, in Virginia, and far beyond its limits, over an area of unknown extent, they form a stratum of eighteen feet in thickness, and similar deposits are found to alternate in the neighbourhood of the Mediterranean with calcareous strata chiefly composed of Foraminifera. At first sight it may seem a gross exaggeration to attribute so vast an agency to beings individually so minute, but when we recollect how quickly they multiply by division, and how their activity dates from the first dawn of organic creation, their architectural powers no longer seem incredible. In forty-eight hours a single diatom may multiply to 8,000,000, and in four days to 140,000,000,000,000, when the silicious coverings of its enormous progeny will already suffice to fill up a space of two cubic feet. No wonder, then, that during the course of ages these microscopic plants have been able to form prodigious strata wherever circumstances favoured their propagation. In no case is the power of numbers more forcibly exemplified, for where can we find results more vast, proceeding from the infinite multiplication of the smallest individuals, than that whole tracts of country should literally be built up of the skeletons of Foraminifera and DiatomaceÆ?