Note 7 — PHYSIOGNOMY OF PLANTS.

p. 8.—“The collected labours of united Lithophytes.”

Following Linnæus and Ellis, the calcareous zoophytes,—among which Madrepores, Meandrinæ, Astreæ, and Pocilloporæ, especially, produce wall-like coral-reefs,—are inhabited by living creatures which were long believed to be allied to the Nereids belonging to Cuvier’s Annelidæ. The anatomy of these gelatinous little creatures has been elucidated by the ingenious and extensive researches of Cavolini, Savigny, and Ehrenberg. We have learnt that in order to understand the entire organization of what are called the rock-building coral animals, the scaffolding which survives them, i. e., the layers of lime, which in the form of thin delicate plates or lamellæ are elaborated by vital functions, must not be regarded as something extraneous to the soft membranes of the food-receiving animal.

Besides the more extended knowledge of the wonderful formation of the animated coral stocks, there have been gradually established more accurate views respecting the influence exercised by corals on other departments of Nature,—on the elevation of groups of low islands above the level of the sea,—on the migrations of land-plants and the successive extension of the domains of particular Floras,—and, lastly, in some parts of the ocean, on the diffusion of races of men, and the spread of particular languages.

As minute organic creatures living in society, corals do indeed perform an important part in the general economy of Nature, although they do not, as was begun to be believed at the time of Cook’s voyages, enlarge continents and build up islands from fathomless depths of the ocean. They excite the liveliest interest, whether considered as subjects of physiology and of the study of the gradation of animal forms, or whether they are regarded in reference to their influence on the geography of plants and on the geological relations of the crust of the Earth. According to the great views of Leopold von Buch, the whole formation of the Jura consists of “large raised coral-banks of the ancient world surrounding the ancient mountain chains at a certain distance.”

In Ehrenberg’s Classification, (Abhandlungen der Akad. der Wiss. zu Berlin aus dem, J. 1882, S. 393-432) Coral-animals, (often improperly called, in English works, Coral-insects) are divided into two great classes: the single-mouthed Anthozoa, which are either free or capable of detaching themselves, being the animal-corals, Zoocorallia; and those in which the attachment is permanent and plant-like, being the Phyto-corals. To the first order, the Zoocorallia, belong the Hydras or Arm-polypi of Trembley, the Actiniæ decked with beautiful colours, and the mushroom-corals; to the second order or Phyto-corals belong the Madrepores, the Astræids, and the Ocellinæ. The Polypi of the second order are those which, by the cellular wave-defying ramparts which they construct, are the principal subject of the present note. These ramparts consist of an aggregate of coral trunks, which, however, do not instantly lose their common vitality as does a forest tree when cut down.

Every coral-trunk is a whole which has arisen by a formation of buds taking place according to certain laws, the parts of which the whole consists forming a number of organically distinct individuals. In the group of Phyto-corals these individuals cannot detach themselves at pleasure, but remain united with each other by thin plates of carbonate of lime. It is not, therefore, by any means the case that each trunk of coral has a central point of common vitality or life. (See Ehrenberg’s Memoir above referred to, S. 419.) The propagation of coral-animals takes place, in the one order, by eggs or by spontaneous division; and in the other order, by the formation of buds. It is the latter mode of propagation which, in the development of individuals, is the most rich in variety of form.

Coral-reefs, (according to the definition of Dioscorides, sea-plants, a forest of stone-trees, Lithodendra), are of three kinds;—coast reefs, called by the English “shore or fringing reefs,” which are immediately connected with the coasts of continents or islands, as almost all the coral banks of the Red Sea seen during an eighteen months’ examination by Ehrenberg and Hemprich;—“barrier-reefs,” “encircling-reefs,” as the great Australian barrier-reef on the north-east coast of New Holland, extending from Sandy Cape to the dreaded Torres Strait; and as the encircling-reefs surrounding the islands of Vanikoro (between the Santa Cruz group and the New Hebrides) and Poupynete (one of the Carolinas);—and lastly, coral banks enclosing lagoons, forming “Atolls” or “Lagoon-islands.” This highly natural division and nomenclature have been introduced by Charles Darwin, and are intimately connected with the explanation which that ingenious and excellent investigator of nature has given of the gradual production of these wonderful forms. As on the one hand Cavolini, Ehrenberg, and Savigny have perfected the scientific-anatomical knowledge of the organisation of coral-animals, so on the other hand the geographical and geological relations of coral-islands have been investigated and elucidated, first by Reinhold and George Forster in Cook’s Second Voyage, and subsequently, after a long interval, by Chamisso, Péron, Quoy and Gaimard, Flinders, Lütke, Beechey, Darwin, d’Urville, and Lottin.

The coral-animals and their stony cellular structures or scaffolding belong principally to the warm tropical seas, and the reefs are found more frequently in the Southern than in the Northern Hemisphere. The Atolls or Lagoon Islands are crowded together in what has been called the Coral-Sea, off the north-east coast of New Holland, including New Caledonia, the Salomon’s Islands, and the Louisiade Archipelago; in the group of the Low islands (Low Archipelago), eighty in number; in the Fidji, Ellice, and Gilbert groups; and in the Indian Ocean, on the north-east of Madagascar, under the name of the Atoll-group of Saya de Malha.

The great Chagos bank, of which the structure and rocks of dead coral have been thoroughly examined by Captain Moresby and by Powell, is so much the more interesting, because we may regard it as a continuation of the more northerly Laccadives and Maldives. I have already called attention elsewhere (Asie Centrale, T. i. p. 218), to the importance of the succession of these Atolls, running exactly in the direction of a meridian and continued as far as 7° south latitude, to the general system of mountains and the configuration of the earth’s surface in Central Asia. They form a kind of continuation to the great rampart-like mountain elevations of the Ghauts and the more northern chain of Bolor, to which correspond in the trans-Gangetic Peninsula the North and South Chains which are intersected near the great bend of the Thibetian Tzang-bo River by several transverse mountain systems running east and west. In this eastern peninsula are situated the chains of Cochin China, Siam, and Malacca which are parallel with each other, as well as those of Ava and Arracan which all, after courses of unequal length, terminate in the Gulfs or Bays of Siam, Martaban, and Bengal. The Bay of Bengal appears like an arrested attempt of nature to form an inland sea. A deep invasion of the ocean, between the simple western system of the Ghauts, and the eastern very complex trans-Gangetic system of mountains, has swallowed up a large portion of the low lands on the eastern side, but met with an obstacle more difficult to overcome in the existence of the extensive high plateau of Mysore.

Such an invasion of the ocean has occasioned two almost pyramidal peninsulas of very different dimensions, and differently proportioned in breadth and length; and the continuations of two mountain systems (both running in the direction of the meridian, i. e., the mountain system of Malacca on the east, and the Ghauts of Malabar on the west), shew themselves in submarine chains of mountains or symmetrical series of islands, on the one side in the Andaman and Nicobar Islands which are very poor in corals, and on the other side in the three long-extended groups or series of Atolls of the Laccadives, the Maldives, and Chagos. The latter series, called by navigators the Chagos-bank, forms a lagoon encircled by a narrow and already much broken, and in great measure submerged, coral reef. The longer and shorter diameters of this lagoon, or its length and breadth, are respectively 90 and 70 geographical miles. Whilst the enclosed lagoon is only from seventeen to forty fathoms deep, the depth of water at a small distance from the outer margin of the coral, (which appears to be gradually sinking), is such, that at half a mile no bottom was found in sounding with a line of 190 fathoms, and, at a somewhat greater distance, none with 210 fathoms. (Darwin, Structure of Coral Reefs, p. 39, 111, and 183.) At the coral lagoon called Keeling-Atoll, Captain Fitz-Roy, at a distance of only two thousand yards from the reef, found no soundings with 1200 fathoms.

“The corals which, in the Red Sea, form thick wall-like masses, are species of Meandrina, Astræa, Favia, Madrepora (Porites), Pocillopora (hemprichii), Millepora, and Heteropora. The latter are among the most massive, although they are somewhat branched. The corals which lie deepest below the surface of the water in this locality, and which, being magnified by the refraction of the rays of light, appear to the eye like the domes or cupolas of a cathedral or other large building, belong, so far as we were enabled to judge, to Meandrina and Astræa.” (Ehrenberg, manuscript notices.) It is necessary to distinguish between separate and in part free and detached polypifers, and those which form wall-like structures and rocks.

If we are struck with the great accumulation of building polypifers in some regions of the globe, it is not less surprising to remark the entire absence of their structures in other and often nearly adjoining regions. These differences must be determined by causes which have not yet been thoroughly investigated; such as currents, local temperature of the water, and abundance or deficiency of appropriate food. That certain thin-branched corals, with less deposit of lime on the side opposite to the opening of the mouth, prefer the repose of the interior of the lagoon, is not to be denied; but this preference for the unagitated water must not, as has too often been done (Annales des Sciences Naturelles, 1825, T. vi. p. 277), be regarded as a property belonging to the entire class. According to Ehrenberg’s experience in the Red Sea, that of Chamisso in the Atolls of the Marshall Islands east of the Caroline group, the observations of Captain Bird Allen in the West Indies, and those of Capt. Moresby in the Maldives, living Madrepores, Millepores, and species of Astræa and of Meandrina, can support the most violent action of the waves,—“a tremendous surf,”—(Darwin, Coral Reefs, pp. 63-65), and even appear to prefer the most stormy exposure. The living organic forces or powers regulating the cellular structure, which with age acquires the hardness of rock, resist with wonderful success the mechanical forces acting in the shock of the agitated water.

In the Pacific, the Galapagos Islands, and the whole Western Coast of America, are entirely without coral reefs, although so near to the many Atolls of the Low Islands, and the Archipelago of the Marquesas. This absence of corals might perhaps be ascribed to the presence of colder water, since we know that the coasts of Chili and Peru are washed by a cold current coming from the south and turning to the westward off Punta Parina, the temperature of which I found, in 1802, to be only 12°.5 Reaumur (60°.2 Fah.), while the undisturbed adjacent masses of water were from 22° to 23° Reaumur (81°.5 to 83°.8 Fah.); and there are also among the Galapagos small currents running between the islands, having a temperature of only 11°.7 Reaumur (58°.2 Fah.) But these lower temperatures do not extend farther to the north along the shores of the Pacific, and are not found upon the coasts of Guayaquil, Guatimala, and Mexico; nor does a low temperature prevail at the Cape de Verd Islands on the West Coast of Africa, or at the small islands of St. Paul (St. Paul’s rocks), or at St. Helena, Ascension, or San Fernando Noronha,—which yet are all without coral reefs.

While this absence of coral reefs appears to characterise the western coasts of Africa, America, and Australia, on the other hand such reefs abound on the eastern coasts of tropical America, of Africa, on the coasts of Zanzibar and Australia, and on that of New South Wales. The coral banks which I have chiefly had opportunities of observing are those of the interior of the Gulf of Mexico, and those to the south of the Island of Cuba, in what are called the “Gardens of the King and Queen” (Jardines y Jardinillos del Rey y de la Reyna). It was Columbus himself who, on his second voyage, in May 1494, gave that name to this little group of islands, because the agreeable mixture of the silver-leaved arborescent Tournefortia gnapholoides, flowering species of Dolichos, Avicennia nitida, and mangrove hedges, gave to the coral islands the appearance of a group of floating gardens. “Son Cayos verdes y graciosos llenos de arboledas,” says the Admiral. On the passage from Batabano to Trinidad de Cuba, I remained several days in these gardens, situated to the east of the larger island, called the Isla de Pinos, which is rich in mahogany trees: my stay was for the purpose of determining the longitude of the different keys (Cayos). The Cayo Flamenco, Cayo Bonito, Cayo de Diego Perez, and Cayo de piedras, are coral islands rising only from eight to fourteen inches above the level of the sea. The upper edge of the reef does not consist simply of blocks of dead coral; it is rather a true conglomerate, in which angular pieces of coral, cemented together with grains of quartz, are embedded. In the Cayo de piedras I saw such embedded pieces of coral measuring as much as three cubic feet. Several of the small West Indian coral islands have fresh water, a phenomenon which, wherever it presents itself, (for example, at Radak in the Pacific; see Chamisso in Kotzebue’s Entdeckungs-Reise, Bd. iii. S. 108), is deserving of examination, as it has sometimes been ascribed to hydrostatic pressure operating from a distant coast, (as at Venice, and in the Bay of Xagua east of Batabano), and sometimes to the filtration of rain water. (See my Essai politique sur l’Ile de Cuba, T. ii. p. 137.)

The living gelatinous investment of the stony calcareous part of the coral attracts fish, and even turtles, who seek it as food. In the time of Columbus the now unfrequented locality of the Jardines del Rey was enlivened by a singular kind of fishery, in which the inhabitants of the coasts of the Island of Cuba engaged, and in which they availed themselves of the services of a small fish. They employed in the capture of turtle the Remora, once said to detain ships (probably the Echeneis Naucrates), called in Spanish “Reves,” or reversed, because at first sight his back and abdomen are mistaken for each other. The remora attaches itself to the turtle by suction through the interstices of the indented and moveable cartilaginous plates which cover the head of the latter, and “would rather,” says Columbus, “allow itself to be cut in pieces than lose its hold.” The natives; therefore, attach a line, formed of palm fibres, to the tail of the little fish, and after it has fastened itself to the turtle draw both out of the water together. Martin Anghiera, the learned secretary of Charles V., says, “Nostrates piscem reversum appellant, quod versus venatur. Non aliter ac nos canibus gallicis per æquora campi lepores insectamur, illi (incolæ Cubæ insulæ) venatorio pisce pisces alios capiebant.” (Petr. Martyr, Oceanica, 1532, Dec. I. p. 9; Gomara, Hist. de las Indias, 1553, fol. xiv.) We learn by Dampier and Commerson that this piscatorial artifice, the employing a sucking-fish to catch other inhabitants of the water, is much practised on the East Coast of Africa, at Cape Natal and on the Mozambique Channel, and also in the Island of Madagascar. (Lacépède, Hist. nat. des Poissons, T. i. p. 55.) The same necessities combine with a knowledge of the habits of animals to induce the same artifices and modes of capture among nations who are entirely unconnected with each other.

Although, as we have already remarked, the zone included between 22 or 24 degrees of latitude on either side of the equator, appears to be the true region of the calcareous saxigenous lithophytes which raise wall-like structures, yet coral reefs are also found, favoured it is supposed by the warm current of the Gulf-stream, in lat. 32° 23´, at the Bermudas, where they have been extremely well described by Lieutenant Nelson. (Transactions of the Geological Society, 2d Series, 1837, Vol. V. Pt. i. p. 103.) In the southern hemisphere, corals, (Millepores and Cellepores), are found singly as far south as Chiloe, the Archipelago of Chonos, and Tierra de Fuego, in 53° lat.; and Retepores are even found in lat. 72½°.

Since the second voyage of Captain Cook there have been many defenders of the hypothesis put forward by him as well as by Reinhold and George Forster, according to which the low coral islands of the Pacific have been built up by living creatures from the depths of the bottom of the sea. The distinguished investigators of nature, Quoy and Gaimard, who accompanied Captain Freycinet in his voyage round the world in the frigate Uranie, were the first who ventured, in 1823, to express themselves with great boldness and freedom in opposition to the views of the two Forsters (father and son), of Flinders, and of Péron. (Annales des Sciences Naturelles, T. vi., 1825, p. 273.) “En appelant l’attention des naturalistes sur les animalcules des coraux, nous espérons démontrer que tout ce qu’on a dit ou cru observer jusqu’à ce jour relativement aux immenses travaux qu’il sont susceptibles d’exécuter, est le plus souvent inexact et toujours excessivement exagéré. Nous pensons que les coraux, loin d’élever des profondeurs de l’océan des murs perpendiculaires, ne forment que des couches ou des encroûtemens de quelques toises d’èpaisseur.” Quoy and Gaimard also propounded (p. 289) the conjecture that the Atolls, (coral walls enclosing a lagoon), probably owed their origin to submarine volcanic craters. Their estimate of the depth below the surface of the sea at which the animals which form the coral reefs (the species of Astræa, for example) could live, was doubtless too small, being at the utmost from 25 to 30 feet (26½ to 32 E.) An investigator and lover of nature who has added to his own many and valuable observations a comparison with those of others in all parts of the globe, Charles Darwin, places with greater certainty the depth of the region of living corals at 20 to 30 fathoms. (Darwin, Journal, 1845, p. 467; and the same writer’s Structure of Coral Reefs, p. 84-87; and Sir Robert Schomburgk, Hist. of Barbadoes, 1848, p. 636.) This is also the depth at which Professor Edward Forbes found the greatest number of corals in the Egean Sea: it is his “fourth region” of marine animals in his very ingenious memoir on the “Provinces of Depth” and the geographical distribution of Mollusca at vertical distances from the surface. (Report on Ægean Invertebrata in the Report of the 13th Meeting of the British Association, held at Cork in 1843, pp. 151 and 161.) The depths at which corals live would seem, however, to be very different in different species, and especially in the more delicate ones which do not form such large masses.

Sir James Ross, in his Antarctic Expedition, brought up corals with the sounding lead from great depths, and entrusted them to Mr. Stokes and Professor Forbes for more thorough examination. On the west of Victoria Land, near Coulman Island, in S. lat. 72° 31´, at a depth of 270 fathoms, Retepora cellulosa, a species of Hornera, and Prymnoa Rossii, were found quite fresh and living. Prymnoa Rossii is very analogous to a species found on the coast of Norway. (See Ross, Voyage of Discovery in the Southern and Antarctic Regions, vol. i. pp. 334 and 337.) In a similar manner in the high northern regions the whalers have brought up Umbellaria grænlandica, living, from depths of 236 fathoms. (Ehrenberg, in the Abhandl. der Berl. Akad. aus dem J. 1832, S. 430.) We find similar relations of species and situation among sponges, which, indeed, are now considered to belong rather to plants than to zoophytes. On the coasts of Asia Minor the common sponge is found by those engaged in the fishery at depths varying from 5 to 30 fathoms; whereas a very small species of the same genus is not found at a less depth than 180 fathoms. (Forbes and Spratt, Travels in Lycia, 1847, Vol. ii. p. 124.) It is difficult to divine the reason which prevents Madrepores, Meandrina, Astræa, and the entire group of tropical Phyto-corals which raise large cellular calcareous structures, from living in strata of water at a considerable depth below the surface of the sea. The diminution of temperature in descending takes place but slowly; that of light almost equally so; and the existence of numerous Infusoria at great depths shews that the polypifers would not want for food.

In opposition to the hitherto generally received opinion of the entire absence of organic life in the Dead Sea, it is deserving of notice that my friend and fellow labourer, M. Valenciennes, has received through the Marquis Charles de l’Escalopier, and also the French consul Botta, fine specimens of Porites elongata from the Dead Sea. This fact is the more interesting because this species is not found in the Mediterranean, but belongs to the Red Sea, which, according to Valenciennes, has but few organic forms in common with the Mediterranean. I have before remarked that in France a sea fish, a species of Pleuronectes, advances far up the rivers into the interior of the country, thus becoming accustomed to gill-respiration in fresh water; so we find that the coral-animal above spoken of, the Porites elongata of Lamarck, has a not less remarkable flexibility of organisation, since it lives in the Dead Sea, which is over-saturated with salt, and in the open ocean near the Seychelle Islands. (See my Asie Centrale, T. ii. p. 517.)

According to the most recent chemical analyses made by the younger Silliman, the genus Porites, as well as many other cellular polypifers, (Madrepores, Andræas, and Meandrinas of Ceylon and the Bermudas), contain, besides 92-95 per cent. of carbonate of lime and magnesia, some fluoric and phosphoric acids. (See p. 124-131 of “Structure and Classification of Zoophytes,” by James Dana, Geologist of the United States’ Exploring Expedition, under the command of Captain Wilkes.) The presence of fluorine in the solid parts of polypifers reminds us of the fluorate of lime in the bones of fishes, according to the experiments of Morechini and Gay Lussac at Rome. Silex is only found mixed in very small quantity with fluorate and phosphate of lime in coral stocks; but a coral-animal allied to the Horn-coral, Gray’s Hyalonema, has an axis of pure fibres of silex resembling a queue or braided tress of hair. Professor Forchhammer, who has been lately engaged in a thorough analysis of the sea-water from the most different parts of the globe, finds the quantity of lime in the Caribbean Sea remarkably small, being only 247 parts in ten thousand, while in the Categat it amounts to 371 parts in ten thousand. He is disposed to attribute this difference to the many coral-banks among the West Indian Islands, which appropriate the lime, and lower the per centage remaining in the sea-water. (Report of the 16th Meeting of the British Association for the Advancement of Science, held in 1846, p. 91.)

Charles Darwin has developed in a very ingenious manner the probable genetic connection between fringing or shore-reefs, island-encircling reefs, and lagoon-islands, i. e., narrow ring-shaped reefs enclosing interior lagoons. According to his views these three varieties of form are dependent on the oscillating condition of the bottom of the sea, or on periodic elevations and subsidences. The hypothesis which has been several times put forward, according to which the closed ring or annular form of the coral-reefs in Atolls or Lagoon Islands marks the configuration of a submarine volcano, the structure having been raised on the margin of the crater, is opposed by their great dimensions, the diameters of many of them being 30, 40, and sometimes even 60 geographical miles. Our fire-emitting mountains have no such craters; and if we would compare the lagoon, with its submerged interior and narrow enclosing reef, to one of the annular mountains of the moon, we must not forget that those lunar mountains are not volcanoes, but wall-surrounded districts. According to Darwin, the process of formation is the following:—He supposes a mountainous island surrounded by a coral-reef, (a “fringing reef” attached to the shore), to undergo subsidence: the “fringing reef” which subsides with the island is continually restored to its level by the tendency of the coral-animals to regain the surface of the sea, and becomes thus, as the island gradually sinks and is reduced in size, first an “encircling reef” at some distance from the included islet, and subsequently, when the latter has entirely disappeared, an atoll. According to this view, in which islands are regarded as the culminating points of a submerged land, the relative positions of the different coral islands would disclose to us that which we could hardly learn by the sounding line, concerning the configuration of the land which was above the surface of the sea at an earlier epoch. The entire elucidation of this attractive subject, (to the connection of which with the migrations of plants and the diffusion of races of men attention was called at the commencement of the present note), can only be hoped for when inquirers shall have succeeded in obtaining greater knowledge than is now possessed of the depth and the nature of the rocks on which the lowest strata of the dead corals rest.