Flocks of swift-looted ostriches and herds of gazelles wander over this boundless space. With the exception of the newly discovered group of Oases, rich in springs, whose verdant banks are frequented by nomadic tribes of Tibbos and Tuarycks[8], the whole of the African deserts may be regarded as uninhabitable by man. It is only periodically that the neighbouring civilized nations venture to traverse them. On tracks whose undeviating course was determined by commercial intercourse thousands of years ago, the long line of caravans passes from Tafilet to Timbuctoo, or from Mourzouk to Bornou; daring enterprises, the practicability of which depends on the existence of the camel, _the ship of the desert_[9], as it is termed in the ancient legends of the East. These African plains cover an area which exceeds almost three times that of the neighbouring Mediterranean. They are situated partly within and partly near the tropics, a position on which depends their individual natural character. On the other hand, in the eastern portion of the old continent the same geognostic phenomenon is peculiar to the temperate zone. On the mountainous range of Central Asia, between the Gold or Altai Mountain and the Kouen-lien[10], from the Chinese wall to the further side of the Celestial Mountains, and towards the Sea of Aral, over a space of several thousand miles, extend, if not the highest, certainly the largest Steppes in the world. I myself enjoyed an opportunity, full thirty years after my South American travels, of visiting that portion of the Steppes which is occupied by Kalmuck-Kirghis tribes, and is situated between the Don, the Volga, the Caspian Sea, and the Chinese Lake of Dsaisang, and which consequently extends over an area of nearly 2,800 geographical miles. The vegetation of the Asiatic Steppes, which are sometimes hilly and interspersed with pine forests, is in its groupings far more varied than that of the Llanos and the Pampas of Caracas and Buenos Ayres. The more beautiful portions of the plains, inhabited by Asiatic pastoral tribes, are adorned with lowly shrubs of luxuriant white-blossomed Rosaceæ, Crown Imperials (Fritillariæ), Cypripedeæ, and Tulips. As the torrid zone is in general distinguished by a tendency in the vegetable forms to become arborescent, so we also find, that some of the Asiatic Steppes of the temperate zone are characterized by the remarkable height to which flowering plants attain; as, for instance, Saussureæ, and other Synanthereæ; all siliquose plants, and particularly numerous species of Astragalus. On crossing the trackless portions of the herb-covered Steppes in the low carriages of the Tartars, it is necessary to stand upright in order to ascertain the direction to be pursued through the copse-like and closely crowded plants that bend under the wheels. Some of these Steppes are covered with grass; others with succulent, evergreen, articulated alkaline