Note 5 — PHYSIOGNOMY OF PLANTS.

p. 7.—“Shine like stars.”

The luminosity of the ocean is one of those superb natural phenomena which continue to excite our admiration even when we have seen them recur every night for months. The sea is phosphorescent in every zone; but those who have not witnessed the phenomenon within the tropics, and especially in the Pacific, have only an imperfect idea of the grand and majestic spectacle which it affords. When a man-of-war, impelled by a fresh breeze, cuts the foaming waves, the voyager standing at the ship’s side feels as if he could never be satisfied with gazing on the spectacle which presents itself to his view. Every time that in the rolling of the vessel her side emerges from the water, blue or reddish streams of light appear to dart upwards like flashes of lightning from her keel. Nor can I describe the splendour of the appearance presented on a dark night in the tropic seas by the sports of a troop of porpoises. As they cut through the foaming waves, following each other in long winding lines, one sees their mazy track marked by intense and sparkling light. In the Gulf of Cariaco, between Cumana and the Peninsula of Maniquarez, I have stood for hours enjoying this spectacle.

Le Gentil and the elder Forster attributed the flashing to the electric friction excited by the ship in moving through the water, but the present state of our knowledge does not permit us to receive this as a valid explanation. (Joh. Reinh. Forster’s Bemerkungen auf seiner Reise um die Welt, 1783, S. 57; Le Gentil, Voyage dans les Mers de l’Inde, 1779, T. i. p. 685-698.)

Perhaps there are few natural subjects of observation which have been so long and so much debated as the luminosity of the waters of the sea. What we know with certainty on the subject may be reduced to the following simple facts. There are several luminous animals which, when alive, give out at pleasure a faint phosphoric light: this light is, in most instances, rather bluish, as in Nereis noctiluca, Medusa pelagica var. β (Forskäl, Fauna Ægyptiaco-arabica, s. Descriptiones animalium quæ in itinere orientali observavit, 1775, p. 109), and in the Monophora noctiluca, discovered in Baudin’s expedition, (Bory de St.-Vincent, Voyage dans les Iles des Mers d’Afrique, 1804, T. i. p. 107, pl. vi.) The luminous appearance of the sea is due partly to living animals, such as are spoken of above, and partly to organic fibres and membranes derived from the destruction of these living torch-bearers. The first of these causes is undoubtedly the most usual and most extensive. In proportion as travellers engaged in the investigation of natural phenomena have become more zealous in their researches, and more experienced in the use of excellent microscopes, we have seen in our zoological systems the groups of Mollusca and Infusoria, which become luminous either at pleasure or when excited by external stimulus, increase more and more.

The luminosity of the sea, so far as it is produced by living organic beings, is principally due, in the class of Zoophytes, to the Acalephæ (the families of Medusa and Cyanea), to some Mollusca, and to a countless host of Infusoria. Among the small Acalephæ, the Mammaria scintillans offers the beautiful spectacle of, as it were, the starry firmament reflected by the surface of the sea. This little creature, when full grown, hardly equals in size the head of a pin. Michaelis, at Kiel, was the first to show that there are luminous siliceous-shelled infusoria: he observed the flashing light of the Peridinium (a ciliated animalcule), of the cuirassed Monad the Prorocentrum micans, and of a rotifera to which he gave the name of Synchata baltica. (Michaelis über das Leuchten der Ostsee bei Kiel, 1830, S. 17.) The same Synchata baltica was subsequently discovered by Focke in the Lagunes of Venice. My distinguished friend and Siberian travelling companion, Ehrenberg, has succeeded in keeping luminous infusoria from the Baltic alive for almost two months in Berlin. He shewed them to me in 1832 with a microscope in a drop of sea-water: placed in the dark I saw their flashes of light. The largest of these little infusoria were 1-8th, and the smallest from 1-48th to 1-96th of a Paris line in length (a Paris line is about nine-hundredths of an English inch): after they were exhausted, and had ceased to send forth sparkles of light, the flashing was renewed on their being stimulated by the addition of acids or of a little alcohol to the sea-water.

By repeatedly filtering water taken up fresh from the sea, Ehrenberg succeeded in obtaining a fluid in which a greater number of these luminous creatures were concentrated. (Abhandlungen der Akad. der Wiss. zu Berlin aus dem J. 1833, S. 307; 1834, S. 537-575; 1838, S. 45 and 258.) This acute observer has found in the organs of the Photocaris, which emits flashes of light either at pleasure or when irritated or stimulated, a cellular structure with large cells and gelatinous interior resembling the electric organs of the Gymnotus and the Torpedo. “When the Photocaris is irritated, one sees in each cirrus a kindling and flickering of separate sparks, which gradually increase in intensity until the whole cirrus is illuminated; until at last the living fire runs also over the back of the small Nereis-like animal, so that it appears in the microscope like a thread of sulphur burning with a greenish-yellow light. It is a circumstance very deserving of attention, that in the Oceania (Thaumantias) hemisphærica the number and situation of the sparks correspond exactly with the thickened base of the larger cirri or organs which alternate with them. The exhibition of this wreath of fire is a vital act, and the whole development of light is an organic vital process which in the Infusoria shows itself as an instantaneous spark of light, and is repeated after short intervals of repose.” (Ehrenberg über das Leuchten des Meeres, 1836, S. 110, 158, 160, and 163.)

According to these suppositions, the luminous creatures of the ocean show the existence of a magneto-electric light-evolving process in other classes of animals than fishes, insects, Mollusca, and Acalephæ. Is the secretion of the luminous fluid which is effused in some luminous creatures, and which continues to shine for some time without any farther influence of the living animal (for example, in Lampyrides and Elaterides, in the German and Italian glow-worms, and in the South American Cucuyo which lives on the sugar-cane), only a consequence of the first electric discharge, or is it simply dependent on chemical mixture? The shining of insects surrounded by air has doubtless other physiological causes than those which occasion the luminosity of inhabitants of the water, fishes, Medusæ, and Infusoria. The small Infusoria of the ocean, being surrounded by strata of salt water which is a good conducting fluid, must be capable of an enormous electric tension of their light-flashing organs to enable them to shine so intensely in the water. They strike like Torpedos, Gymnoti, and the Tremola of the Nile, through the stratum of water; while electric fishes, in connexion with the galvanic circuit, decompose water and impart magnetism to steel bars, as I showed more than half a century ago (Versuche über die gereizte Muskel- und Nervenfaser, Bd. i. S. 438-441, and see also Obs. de Zoologie et d’Anatomie comparée, vol. i. p. 84); and as John Davy has since confirmed (Phil. Trans, for 1834, Part ii. p. 545-547), do not pass a flash through the smallest intervening stratum.

The considerations which have been developed make it probable that it is one and the same process which operates in the smallest living organic creatures, so minute that they are not perceived by the naked eye,—in the combats of the serpent-like gymnoti,—in flashing luminous infusoria which raise the phosphorescence of the sea to such a degree of brilliancy;—as well as in the thunder-cloud, and in the auroral, terrestrial, or polar light (silent magnetic lightnings), which, as the result of an increased tension in the interior of the globe, are announced for hours beforehand by the suddenly altered movements of the magnetic needle. (See my letter to the Editor of the Annalen der Physik und Chemie, Bd. xxxvii. 1836, S. 242-244).

Sometimes one cannot even with high magnifying powers discern any animalcules in the luminous water; and yet, whenever the wave strikes and breaks in foam against a hard body, a light is seen to flash. In such case the cause of the phenomenon probably consists in the decaying animal fibres, which are disseminated in immense abundance throughout the body of water. If this luminous water is filtered through fine and closely woven cloths, these little fibres and membranes are separated in the shape of shining points. When we bathed at Cumana in the waters of the Gulf of Cariaco, and afterwards lingered awhile on the solitary beach in the mild evening air without our clothes, parts of our bodies continued luminous from the shining organic particles which had adhered to the skin, and the light only became extinct at the end of some minutes. Considering the enormous quantity of animal life in all tropical seas, it is, perhaps, not surprising that the sea water should be luminous, even where no visible organic particles can be detached from it. From the almost infinite subdivision of the masses of dead Dagysæ and Medusæ, the sea may perhaps be looked on as a gelatinous fluid, which as such is luminous, distasteful to, and undrinkable by man, and capable of affording nourishment to many fish. If one rubs a board with part of a Medusa hysocella, the part so rubbed regains its luminosity on friction with a dry finger. On my passage to South America I sometimes placed a Medusa on a tin plate. When I struck another metallic substance against the plate, the slightest vibrations of the tin were sufficient to cause the light. What is the manner in which in this case the blow and the vibrations act? Is the temperature momentarily augmented? Are new surfaces exposed? or does the blow press out a fluid, such as phosphuretted hydrogen, which may burn on coming into contact with the oxygen of the atmosphere or of the air held in solution by the sea-water. This light-exciting influence of a shock or blow is particularly remarkable in a “cross sea,” i. e. when waves coming from opposite directions meet and clash.

I have seen the sea within the tropics appear luminous in the most different states of weather; but the light was most brilliant when a storm was near, or with a sultry atmosphere and a vaporous thickly-clouded sky. Heat and cold appear to have little influence on the phenomenon, for on the Banks of Newfoundland the phosphorescence is often very bright during the coldest winter weather. Sometimes under apparently similar external circumstances the sea will be highly luminous one night and not at all so the following night. Does the atmosphere influence the disengagement of light, or do all these differences depend on the accident of the observer sailing through a part of the sea more or less abundantly impregnated with gelatinous animal substances? Perhaps it is only in certain states of the atmosphere that the light-evolving animalculæ come in large numbers to the surface of the sea. It has been asked why the fresh water of our marshes, which is filled with polypi, is never seen to become luminous. Both in animals and plants, a particular mixture of organic particles appears to be required in order to favour the production of light. Willow-wood is oftener found to be luminous than oak-wood. In England experiments have succeeded in making saltwater shine by pouring into it the liquor from pickled herrings. It is easy to shew by galvanic experiments that in living animals the evolution of light depends on an irritation of the nerves. I have seen an Elater noctilucus which was dying emit strong flashes of light when I touched the ganglion of his fore leg with zinc and silver. Medusæ sometimes shew increased brightness at the moment of completing the galvanic circuit. (Humboldt, Relat. Hist. T. i. p. 79 and 533.)

Respecting the wonderful development of mass and power of increase in Infusoria, see Ehrenberg, Infus. S. xiii. 291 and 512. He observes that “the galaxy of the minutest organisms passes through the genera of Vibrio and Bacterium and that of Monas, (in the latter they are often only ¹⁄₃₀₀₀ of a line,)” S. xix. and 244.