Of all the phenomena which attract the naturalist’s attention, as he wanders over the surface of the earth, there is none which makes a deeper impression on his mind than the omnipresence of life. On the snow-clad cone of Chimborazo, 18,000 feet above the level of the sea, Humboldt found butterflies and other winged insects, while, high over his head, the condor was soaring in solitary majesty. At the still greater elevation of 18,460 feet, at the Doonkiah Pass in the Himalaya Mountains, Dr. Hooker plucked flowering plants, and saw large flocks of wild geese winging their flight above Kunchinjinga (22,750 feet) towards the unknown regions of Central Asia. Thus man meets with life as far as he is able to ascend, or as far as his sight plunges into the atmospheric ocean. Besides the objects visible to his eye, innumerable microscopical organisms pervade the realms of air. According to Ehrenberg’s brilliant discovery, the impalpably fine dust which, wafted by the Harmattan, often falls on ships when hundreds of miles from the coast of Africa, consists of agglomerations of silica-coated diatoms, individually so small as to be invisible to the naked eye; and everywhere numberless minute germs of future life—eggs of insects and sporules of cryptogamic plants—well fitted by cilia and feathery crowns for an aërial journey, float up and down in the atmosphere; while the waters of ocean are found, in like manner, filled with myriads of animated atoms. But organic life not only occupies those parts of our globe which are accessible to solar light; it also dives profoundly into the subterranean world, wherever rain, or the melted snow, filtering through the porous earth, or through vents and crevices, is able to penetrate into natural caverns or artificial mines. For the combination of moisture, warmth, and air is able to develop organic life even thousands of feet below the surface of the earth; while light, though indispensable to most creatures, would blight and destroy the inhabitants of the subterranean vaults. On surveying the flora of these dismal recesses, we find it consisting exclusively of mushrooms or fungi, the lowest forms of vegetation, which, shunning the light, love darkness and damp. Their appearance in the caves is, as everywhere else, dependent upon the existence of an organic basis, and thus they are most commonly found germinating on pieces of wood, particularly in a state of decomposition, which have been conveyed into the caverns either through the agency of man or by the influx of water. Species of a peculiarly luxuriant growth are sometimes seen to spread over the neighbouring stones, or apparently to spring from the rocky ground, where, however, on closer inspection, vestiges of decayed organic substances will generally be detected.