When Nature Does Not Present The Same Species, She Loves To Repeat The Same Genera.

Neighbouring species are often placed at enormous distances from each other, in the low regions of the temperate zone, and on the alpine heights of the equator.

At other times (and the Silla of Caracas affords a striking example of this phenomenon), they are not the European genera, which have sent species to people like colonists the mountains of the torrid zone, but genera of the same tribe, difficult to be distinguished by their appearance, which take the place of each other in different latitudes.

The mountains of New Grenada surrounding the table-lands of Bogota are more than two hundred leagues distant from those of Caracas, and yet the Silla, the only elevated peak in the chain of low mountains, presents those singular groupings of befarias with purple flowers, of andromedas, of gualtherias, of myrtilli, of uvas camaronas,* (* The names vine-tree, and uvas camaronas, are given in the Andes to plants of the genus Thibaudia, on account of their large succulent fruits. Thus the ancient botanists gave the name of bear's vine, uva ursi, and vine of Mount Ida (Vitis idaea), to an arbutus and a myrtillus, which belong, like the thibaudia, to the family of the Ericineae.) of nerteras, and of aralias with hoary leaves,* (* Nertera depressa, Aralia reticulata, Hedyotis blaerioides.) which characterize the vegetation of the paramos on the high Cordilleras of Santa Fe. We found the same Thibaudia glandulosa at the entrance of the table-land of Bogota, and in the Pejual of the Silla. The coast-chain of Caracas is unquestionably connected (by the Torito, the Palomera, Tocuyo, and the paramos of Rosas, of Bocono, and of Niquitao) with the high Cordilleras of Merida, Pamplona, and Santa Fe; but from the Silla to Tocuyo, along a distance of seventy leagues, the mountains of Caracas are so low, that the shrubs of the family of the ericineous plants, just cited, do not find the cold climate which is necessary for their development. Supposing, as is probable, that the thibaudias and the rhododendron of the Andes, or befaria, exist in the paramo of Niquitao and in the Sierra de Merida, covered with eternal snow, these plants would nevertheless want a ridge sufficiently lofty and long for their migration towards the Silla of Caracas.

The more we study the distribution of organized beings on the globe, the more we are inclined, if not to abandon the ideas of migration, at least to consider them as hypotheses not entirely satisfactory. The chain of the Andes divides the whole of South America into two unequal longitudinal parts. At the foot of this chain, on the east and west, we found a great number of plants specifically the same. The various passages of the Cordilleras nowhere permit the vegetable productions of the warm regions to proceed from the coasts of the Pacific to the banks of the Amazon. When a peak attains a great elevation, either in the middle of very low mountains and plains, or in the centre of an archipelago heaved up by volcanic fires, its summit is covered with alpine plants, many of which are again found, at immense distances, on other mountains having an analogous climate.

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