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. In using this expression, it is tacitly admitted, that under the influence of certain temperatures, certain vegetable forms must necessarily be developed. Such a supposition, however, taken in all its generality, is not strictly accurate. The pines of Mexico are wanting on the Cordilleras of Peru. The Silla of Caracas is not covered with the oaks which flourish in New Grenada at the same height. Identity of forms indicates an analogy of climate; but in similar climates the species may be singularly diversified.
The charming rhododendron of the Andes (the befaria) was first described by M. Mutis, who observed it near Pamplona and Santa Fe de Bogota, in the fourth and seventh degree of north latitude. It was so little known before our expedition to the Silla, that it was scarcely to be found in any herbal in Europe. The learned editors of the Flora of Peru had even described it under another name, that of acunna. In the same manner as the rhododendrons of Lapland, Caucasus, and the Alps* (* Rhododendron lapponicum, R. caucasicum, R. ferrugineum, and R. hirsutum.) differ from each other, the two species of befaria we brought from the Silla* (* Befaria glauca, B. ledifolia.) are also specifically different from that of Santa Fe and Bogota.* (* Befaria aestuans, and B. resinosa.) Near the equator the rhododendrons of the Andes (Particularly B. aestuans of Mutis, and two new species of the southern hemisphere, which we have described under the name of B. coarctata, and B. grandiflora.) cover the mountains as far as the highest paramos, at sixteen and seventeen hundred toises of elevation. Advancing northward, on the Silla de Caracas, we find them much lower, a little below one thousand toises. The befaria recently discovered in Florida, in latitude 30 degrees, grows even on hills of small elevation. Thus in a space of six hundred leagues in latitude, these shrubs descend towards the plains in proportion as their distance from the equator augments. The rhododendron of Lapland grows also at eight or nine hundred toises lower than the rhododendron of the Alps and the Pyrenees. We were surprised at not meeting with any species of befaria in the mountains of Mexico, between the rhododendrons of Santa Fe and Caracas, and those of Florida.
In the small grove which crowns the Silla, the Befaria ledifolia is only three or four feet high. The trunk is divided from its root into a great many slender and even verticillate branches. The leaves are oval, lanceolate, glaucous on their inferior part, and curled at the edges. The whole plant is covered with long and viscous hairs, and emits a very agreeable resinous smell. The bees visit its fine purple flowers, which are very abundant, as in all the alpine plants, and, when in full blossom, they are often nearly an inch wide.
The rhododendron of Switzerland, in those places where it grows, at the elevation of between eight hundred and a thousand toises, belongs to a climate, the mean temperature of which is +2 and-1 degrees, like that of the plains of Lapland. In this zone the coldest months are-4, and-10 degrees: the hottest, 12 and 7 degrees. Thermometrical observations, made at the same heights and in the same latitudes, render it probable that, at the Pejual of the Silla, one thousand toises above the Caribbean Sea, the mean temperature of the air is still 17 or 18 degrees; and that the thermometer keeps, in the coolest season, between 15 and 20 degrees in the day, and in the night between 10 and 12 degrees. At the hospital of St. Gothard, situated nearly on the highest limit of the rhododendron of the Alps, the maximum of heat, in the month of August at noon, in the shade, is usually 12 or 13 degrees; in the night, at the same season, the air is cooled by the radiation of the soil down to +1 or-1.5 degrees. Under the same barometric pressure, consequently at the same height, but thirty degrees of latitude nearer the equator, the befaria of the Silla is often, at noon, in the sun, exposed to a heat of 23 or 24 degrees. The greatest nocturnal refrigeration probably never exceeds 7 degrees. We have carefully compared the climate, under the influence of which, at different latitudes, two groups of plants of the same family vegetate at equal heights above the level of the sea. The results would have been far different, had we compared zones equally distant, either from the perpetual snow, or from the isothermal line of 0 degrees.* (* The stratum of air, the mean temperature of which is 0 degrees, and which scarcely coincides with the superior limit of perpetual snow, is found in the parallel of the rhododendrons of Switzerland at nine hundred toises; in the parallel of the befarias of Caracas, at two thousand seven hundred toises of elevation.)
In the little thicket of the Pejual, near the purple-flowered befaria, grows a heath-leaved hedyotis, eight feet high; the caparosa,* which is a large arborescent hypericum (* Vismia caparosa (a loranthus clings to this plant, and appropriates to itself the yellow juice of the vismia); Davallia meifolia, Heracium avilae, Aralia arborea, Jacq., and Lepidium virginicum. Two new species of lycopodium, the thyoides, and the aristatum, are seen lower down, near the Puerto de la Silla.); a lepidium, which appears identical with that of Virginia; and lastly, lycopodiaceous plants and mosses, which cover the rocks and roots of the trees. That which gives most celebrity in the country to the little thicket, is a shrub ten or fifteen feet high, of the corymbiferous family. The Creoles call it incense (incienso).* (* Trixis nereifolia of M. Bonpland.) Its tough and crenate leaves, as well as the extremities of the branches, are covered with a white wool. It is a new species of Trixis, extremely resinous, the flowers of which have the agreeable odour of storax. This smell is very different from that emitted by the leaves of the Trixis terebinthinacea of the mountains of Jamaica, opposite to those of Caracas. The people sometimes mix the incienso of the Silla with the flowers of the pevetera, another composite plant, the smell of which resembles that of the heliotropium of Peru. The pevetera does not, however, grow on the mountains so high as the zone of the befarias; it vegetates in the valley of Chacao, and the ladies of Caracas prepare from it an extremely pleasant odoriferous water.
We spent a long time in examining the fine resinous and fragrant plants of the Pejual. The sky became more and more cloudy, and the thermometer sank below 11 degrees, a temperature at which, in this zone, people begin to suffer from the cold. Quitting the little thicket of alpine plants, we found ourselves again in a savannah. We climbed over a part of the western dome, in order to descend into the hollow of the Silla, a valley which separates the two summits of the mountain. We there had great difficulties to overcome, occasioned by the force of the vegetation. A botanist would not readily guess that the thick wood covering this valley is formed by the assemblage of a plant of the musaceous family.* (*Scitamineous plants, or family of the plantains.) It is probably a maranta, or a heliconia; its leaves are large and shining; it reaches the height of fourteen or fifteen feet, and its succulent stalks grow near one another like the stems of the reeds found in the humid regions of the south of Europe.* (* Arundo donax.) We were obliged to cut our way through this forest. The negroes walked before with their cutlasses or machetes. The people confound this alpine scitamineous plant with the arborescent gramina, under the name of carice. We saw neither its fruit nor flowers. We are surprised to meet with a monocotyledonous family, believed to be exclusively found in the hot and low regions of the tropics, at eleven hundred toises of elevation; much higher than the andromedas, the thibaudias, and the rhododendron of the Cordilleras.* (* Befaria.) In a chain of mountains no less elevated, and more northern (the Blue Mountains of Jamaica), the Heliconia of the parrots and the bihai, rather grow in the alpine shaded situations.* (* Heliconia psittacorum, and H. bihai. These two heliconias are very common in the plains of Terra Firma.)
Wandering in this thick wood of musaceae or arborescent plants, we constantly directed our course towards the eastern peak, which we perceived from time to time through an opening. On a sudden we found ourselves enveloped in a thick mist; the compass alone could guide us; but in advancing northward we were in danger at every step of finding ourselves on the brink of that enormous wall of rocks, which descends almost perpendicularly to the depth of six thousand feet towards the sea. We were obliged to halt. Surrounded by clouds sweeping the ground, we began to doubt whether we should reach the eastern peak before night. Happily, the negroes who carried our water and provisions, rejoined us, and we resolved to take some refreshment. Our repast did not last long. Possibly the Capuchin father had not thought of the great number of persons who accompanied us, or perhaps the slaves had made free with our provisions on the way; be that as it may, we found nothing but olives, and scarcely any bread. Horace, in his retreat at Tibur, never boasted of a repast more light and frugal; but olives, which might have afforded a satisfactory meal to a poet, devoted to study, and leading a sedentary life, appeared an aliment by no means sufficiently substantial for travellers climbing mountains. We had watched the greater part of the night, and we walked for nine hours without finding a single spring. Our guides were discouraged; they wished to go back, and we had great difficulty in preventing them.