308 PHYSIOGNOMY OF PLANTS. 



If we had sufficient grounds for believing that we are now acquainted 

 with half the phsenogamous plants on the globe, and if we took the 

 number of known species only at one or other of the before-men- 

 tioned 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 y 1 ^), 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 i or -^ part as known. 



The assumption that we already know half the existing species of 

 phaenogamous plants is farther opposed by the following considera- 

 tions. Several thousand species of Monocotyledons and Dycotyledons, 

 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 phaenogamous 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-mentioned consideration renders it so 

 much the more important to remember how almost entirely unac- 

 quainted 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 Pastes ; and 

 south of the Equator, with the Floras of the vast forest region between 

 the Ucayale, the Rio de la Madera, and the Tocantin (three great tribu- 

 taries 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 south- 

 east of Arabia, where the highlands rise to about 6400 English feet 

 above the level of the sea of the countries between the Thian- 

 schan, 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 ' 



