The fructification of diœcious plants was at one time principally ascribed to the agency of the wind. It has been shown by Kölreuter, and also with much ingenuity by Sprengel, that bees, wasps and numerous small winged insects, are the main agents in this process. I use the phrase “main agents”, since I cannot regard it as consonant to nature that fructification should be impossible without the intervention of these insects, as Willdenow has also fully shewn.[[KA]] On the other hand dichogamy, sap-marks, (maculæ indicantes), coloured spots indicating the presence of honey-vessels, and fructification by insects, appear to be almost inseparable from one another.[[KB]]
The statement often repeated since Spallanzani, that the diœcious common hemp (Cannabis sativa), which was introduced into Europe from Persia, bears ripe seeds without being in the neighbourhood of pollen-tubes, has been entirely refuted by more recent investigations. When seeds have been obtained, anthers in a rudimentary state have been found near the ovarium, and these may have been capable of yielding some grains of fructifying pollen. Such hermaphrodism is frequent in the whole family of Urticeæ, but a singular and hitherto unexplained phenomenon is manifested in the forcing-houses at Kew by a small New Holland shrub, the Cœlebogyne of Smith. This phanerogamic plant brings forth seeds in England without exhibiting any trace of male organs, and without the bastard introduction of the pollen of any other plant. “A species of Euphorbiaceæ,” (?) writes the distinguished botanist, Jussieu, “the Cœlebogyne, which, although but recently described, has been cultivated for many years in English conservatories, has several times borne seeds, which were evidently perfect, since the well-formed embryos they contained have produced similar plants. The most careful observations have hitherto failed in discovering the slightest trace of anthers or even pollen in the flowers, which are diœcious. No male plants of this kind are known to exist in England. The embryo cannot therefore have come from the pollen, which is wholly deficient, but must have been formed entirely in the ovule.”[[KC]]
In order to obtain a fresh and confirmatory explanation of this important and isolated physiological phenomenon, I lately addressed myself to my young friend, Dr. Joseph Hooker, who after having accompanied Sir James Ross in his Antarctic voyage, has now joined the great Thibeto-Himalayan expedition. Dr. Hooker wrote to me as follows from Alexandria, at the close of December, 1847, prior to his embarkation at Suez: “Our Cœlebogyne still flowers with my father at Kew, as well as in the Gardens of the Horticultural Society. It ripens its seeds regularly. I have repeatedly examined it with care, but have never been able to discover a penetration of pollen utricles into the stigma, nor any traces of their presence in the latter or in the style. In my herbarium the male blossoms are in small catkins.”
[75]. p. 212—“Like luminous stars.”
The phosphorescence of the ocean is one of those splendid phenomena of nature which excite our admiration, even when we behold its recurrence every night for months together. The ocean is phosphorescent in all zones of the earth, but he who has not witnessed the phenomenon in the tropics, and especially in the Pacific, can form but a very imperfect idea of the majesty of this brilliant spectacle. The traveller on board a man-of-war, when ploughing the foaming waves before a fresh breeze, feels that he can scarcely satisfy himself with gazing on the spectacle presented by the circling waves. Wherever the ship’s side rises above the waves, bluish or reddish flames seem to flash lightning-like upwards from the keel. The appearance presented in the tropical seas on a dark night is indescribably glorious, when shoals of dolphins are seen sporting around, and cutting the foaming waves in long and circling lines, gleaming with bright and sparkling light. In the Gulf of Cariaco, between Cumana and the Peninsula of Maniquarez, I have spent hours in enjoying this spectacle.
Le Gentil and the elder Forster ascribed these flames to the electrical friction of the water on the vessel as it glides forward—an explanation that must, in the present condition of our physical knowledge, be regarded as untenable.[[KD]]
There are probably few subjects of natural investigation which have excited so many and such long-continued contentions as the phosphorescence of sea-water. All that is known with certainty regarding this much disputed question may be reduced to the following simple facts. There are many luminous mollusca which possess the property when alive of emitting at will a faint phosphoric light; which is of a bluish tinge in Nereis noctiluca, Medusa pelagica var. β,[[KE]] and in the pipe-like Monophora noctiluca, discovered in Baudin’s expedition.[[KF]] The luminosity of sea-water is in part owing to living light-bearing animals, and in part to the organic fibres and membranes of the same, when in a state of decomposition. The first-named of these causes of the phosphorescence of the ocean is undoubtedly the most common and the most widely diffused. The more actively and the more efficiently that travellers engaged in the study of nature have learnt to employ powerful microscopes, the more our zoological systems have been enriched by new groups of mollusca and infusoria, whose property of emitting light either at will or from external stimulus has been recognised.
The luminosity of the sea, as far as it depends on living organisms, is principally owing, among zoophytes, to the Acalephæ (the families of Medusæ and Cyaneæ), to some Mollusca, and to an innumerable host of Infusoria. Among the small Acalephæ (Sea-nettles), the Mammaria scintillans presents us, as it were, with the glorious image of the starry firmament reflected in the surface of the sea. When full-grown this little creature scarcely equals in size the head of a pin. The existence of siliceous-shelled luminous infusoria was first shown by Michaelis at Kiel. He observed the coruscation of the Peridinium. (a ciliated animalcule,) of the Cuirass-monad (Prorocentrum micans), and of a rotifer, which he named Synchata baltica,[[KG]] the same that Focke subsequently found in the lagoons of Venice. My distinguished friend and fellow traveller in Siberia, Ehrenberg, succeeded in keeping two luminous Infusoria of the Baltic alive for nearly two months at Berlin. I examined them with him in 1832; and saw them coruscate in a drop of sea-water on the darkened field of the microscope. When these luminous Infusoria (the largest of which was only ⅛ and the smallest from ¹⁄₄₈ to ¹⁄₉₆ of a of a Parisian line in length) were exhausted, and ceased to emit sparks, they would renew their flashing on being stimulated by the addition of acids or by the application of a little alcohol to the sea-water.
By repeatedly filtering fresh sea-water, Ehrenberg succeeded in procuring a fluid in which a large number of these light-emitting animalcules were accumulated.[[KH]] This acute observer has found in the organs of the Photocharis which give off flashes of light (either voluntarily or when stimulated), a cellular structure of a gelatinous character in the interior, and which manifests some similarity with the electric organ of the Gymnotus and the Torpedo. “When the Photocharis is irritated, in each cirrus a kindling and a gleaming of separate sparks may be observed, which gradually increase and at length illuminate the whole cirrus; until the living flame runs also over the back of this nereid-like animalcule, making it appear under the microscope like a burning thread of sulphur with a greenish-yellow light. In the Oceania (Thaumanthias) hemisphærica, the number and position of the sparks correspond accurately, at the thickened base, with the larger cirri or organs which alternate with them, a circumstance that merits special attention. The manifestation of this wreath of fire is an act of vitality, and the whole development of light an organic vital process, which exhibits itself in Infusorial animals as a momentary spark of light, and is repeated after short intervals of rest.”[[KI]]
The luminous animals of the ocean appear, from these conjectures, to prove the existence of a magneto-electric light-generating vital process in other classes of animals besides fishes, insects, mollusca, and acalephæ. Is the secretion of the luminous fluid which is effused in some animalcules, and which continues to shine for a long period without further influence of the living organism (as, for instance, in Lampyrides and Elaterides, in the German and Italian glow-worms, and in the South American Cucuyo of the sugar-cane), merely the consequence of the first electric discharge, or is it simply dependent on chemical composition? The luminosity of insects surrounded by air assuredly depends on physiological causes different from those which give rise to a luminous condition in aquatic animals, fishes, Medusæ, and Infusoria. The small Infusoria of the ocean, being surrounded by strata of salt-water which constitutes a powerful conducting medium, must be capable of an enormous electric tension of their flashing organs to enable them to shine so vividly in the water. They strike like the Torpedo, the Gymnotus, and the Electric Silurus of the Nile, through the stratum of water: whilst electric fishes which, in connection with the galvanic circuit, are capable of decomposing water, and of imparting magnetic power to steel needles. (as I showed more than half a century ago,[[KJ]] and as John Davy has more recently confirmed,[[KK]]) yield no indications of electricity through the smallest intervening stratum of flame.