By This Unceasing Action Of Organic Force The Empire Of Flora Is Extended Over Islands Ravaged By Volcanoes.

On surveying the different zones of the vegetation of Teneriffe, we perceive that the whole island may be considered as a forest of laurels, arbutus, and pines, containing in its centre a naked and rocky soil, unfit either for pasturage or cultivation.

M. Broussonnet observes, that the archipelago of the Canaries may be divided into two groups of islands; the first comprising Lancerota and Forteventura, the second Teneriffe, Canary, Gomera, Ferro, and Palma. The appearance of the vegetation essentially differs in these two groups. The eastern islands, Lancerota and Forteventura, consist of extensive plains and mountains of little elevation; they have very few springs, and bear the appearance, still more than the other islands, of having been separated from the continent. The winds blow in the same direction, and at the same periods: the Euphorbia mauritanica, the Atropa frutescens, and the arborescent Sonchus, vegetate there in the loose sands, and afford, as in Africa, food for camels. The western group of the Canaries presents a more elevated soil, is more woody, and is watered by a greater number of springs.

Though the whole archipelago contains several plants found also in Portugal,* (* M. Willdenouw and myself found, among the plants of the peak of Teneriffe, the beautiful Satyrium diphyllum (Orchis cordata, Willd.) which Mr. Link discovered in Portugal. The Canaries have, in common with the Flora of the Azores, not the Dicksonia culcita, the only arborescent heath found at the thirty-ninth degree of latitude, but the Asplenium palmatum, and the Myrica Faya. This last tree is met with in Portugal, in a wild state. Count Hoffmansegg has seen very old trunks of it; but it was doubtful whether it was indigenous, or imported into that part of our continent. In reflecting on the migrations of plants, and on the geological possibility, that lands sunk in the ocean may have heretofore united Portugal, the Azores, the Canaries, and the chain of Atlas, we conceive, that the existence of the Myrica Faya in western Europe is a phenomenon at least as striking as that of the pine of Aleppo would be at the Azores.), in Spain, at the Azores, and in the north-west of Africa, yet a great number of species, and even some genera, are peculiar to Teneriffe, to Porto Santo, and to Madeira. Such are the Mocanera, the Plocama, the Bosea, the Canarina, the Drusa, and the Pittosporum. A form which may be called northern, that of the cruciform plant (Among the small number of cruciform species contained in the Flora of Teneriffe, we shall here mention Cheiranthus longifolius, l'Herit.; Ch. fructescens, Vent.; Ch. scoparius, Brouss.; Erysimum bicorne, Aiton; Crambe strigosa, and C. laevigata, Brouss.), is much rarer in the Canaries than in Spain and in Greece. Still farther to the south, in the equinoctial regions of both continents, where the mean temperature of the air rises above twenty-two degrees, the cruciform plants are scarcely ever to be seen.

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