OCR Text |
Show 308 PHYSIOGNOMY OF PLANTS. If we had sufficient grounds for believing that we are now acquainted with half the phrenogamous plants on the globe, and if we took the number of known species only at one or other of the before-mentioned numbers of 160,000 or 213,000, we should still have to take the number of grasses (the general proportion of which appears to be -l!!), in the first case at least at 26,000, and in the second case at 35,000 different species, which would give respectively in the two cases only either j or -f"O" part as known. The assumption that we already know half the existing species of phrenogamous plants is farther opposed by the following considerations. Several thousand species of Monocotyledons and Dicotyledons, and among them tall trees-(I refer here to my own Expedition)have been discovered in regions, considerable portions of which had been previously examined by distinguished botanists. The portions of the great continents which have never even been trodden by botanical observers considerably exceed in area those which have been traversed by such travellers, even in a superficial manner. The greatest variety of phrenogamous vegetation, i. e. the greatest number of species on a given area, is found between the tropics, and in the sub-tropical zones. This last-mentiol).ed consideration renders it so much the more important to remember how almost entirely unacquainted we are, on the New Continent, north of the Equator, with the Floras of Oaxaca, Yucatan, Guatimala, Nicaragua, the Isthmus of Panama, Choco, Antioquia, and the Provincia de los Pastos ;-and so~th of the Equator, with the Floras of the vast forest region between the Ucayale, the Rio de laMadera, and the Tocantin (three great tributaries of the Amazons), and with those of Paraguay and the Provincia de los Missiones. In Africa, except in respect to the coasts, we know nothing of the vegetation from 15° north to 20° south latitude; in Asia, we are unacquainted with the Floras of the south and southeast of Arabia, where the highlands rise to about 6400 English feet above the level of the sea-of the countries between the Thianschan, the Kuenliin, and the Himalaya, all the west part of China, and the greater part of the countries beyond the Ganges. Still more unknown to the botanist are the interior of Borneo, New Guinea, and part of Australia. Farther to the south, the number of species undergoes a wonderful diminution, as Joseph Hooker has well and |