I Say The History; For In Vain Would Reason Forbid Man To Form Hypotheses On The Origin Of Things; He Still Goes On Puzzling Himself With Insoluble Problems Relating To The Distribution Of Beings.

A gramen of Switzerland grows on the granitic rocks of the straits of Magellan.* (* Phleum alpinum, examined by Mr. Brown.

The investigations of this great botanist prove that a certain number of plants are at once common to both hemispheres. Potentilla anserina, Prunella vulgaris, Scirpus mucronatus, and Panicum crus-galli, grow in Germany, in Australia, and in Pennsylvania.) New Holland contains above forty European phanerogamous plants: and the greater number of those plants, which are found equally in the temperate zones of both hemispheres, are entirely wanting in the intermediary or equinoctial region, as well in the plains as on the mountains. A downy-leaved violet, which terminates in some sort the zone of the phanerogamous plants at Teneriffe, and which was long thought peculiar to that island,* is seen three hundred leagues farther north, near the snowy summit of the Pyrenees. (* The Viola cheiranthifolia has been found by MM. Kunth and Von Buch among the alpine plants which Jussieu brought from the Pyrenees.) Gramina and cyperaceous plants of Germany, Arabia, and Senegal, have been recognized among those that were gathered by M. Bonpland and myself on the cold table-lands of Mexico, along the burning shores of the Orinoco, and in the southern hemisphere on the Andes and Quito.* (* Cyperus mucronatus, Poa eragrostis, Festuca myurus, Andropogos avenaceus, Lapago racemosa. (See the Nova Genera et Species Plantarum volume 1 page 25.)) How can we conceive the migration of plants through regions now covered by the ocean? How have the germs of organic life, which resemble each other in their appearance, and even in their internal structure, unfolded themselves at unequal distances from the poles and from the surface of the seas, wherever places so distant present any analogy of temperature? Notwithstanding the influence exercised on the vital functions of plants by the pressure of the air, and the greater or less extinction of light, heat, unequally distributed in different seasons of the year, must doubtless be considered as the most powerful stimulus of vegetation.

The number of identical species in the two continents and in the two hemispheres is far less than the statements of early travellers would lead us to believe. The lofty mountains of equinoctial America have certainly plantains, valerians, arenarias, ranunculuses, medlars, oaks, and pines, which from their physiognomy we might confound with those of Europe; but they are all specifically different. 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. Such are the general phenomena of the distribution of plants.

It is now said that a mountain is high enough to enter into the limits of the rhododendrons and the befarias, as it has long been said that such a mountain reached the limit of perpetual snow.

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