ANNOTATIONS AND ADDITIONS. 121 



lieving that we are now acquainted with half the phsenoga- 

 raous plants on the globe, and if we took the number of 

 known species only at one or other of the before-mentioned 

 numbers of 160000 or 213000, we should still have to 

 take the number of grasses (the general proportion of which 

 appears to be 2), in the first case at least at 26000, and 

 in the second case at 35000 different species, which would 

 give respectively in the two cases only either -- or -yV part 

 as known. 



The assumption that we already know half the exist- 

 ing species of phsenogamous plants is farther opposed by 

 the following considerations. 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 ex- 

 ceed in area those which have been traversed by such tra- 

 vellers, even in a superficial manner. The greatest variety 

 of phsenogamous vegetation, *. e. the greatest number of 

 species on a given area, is found between the tropics, and 

 in the sub-tropical zones. This last-mentioned considera- 

 tion renders it so much the more important to re- 

 member 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 south of the equator, with the Floras of the vast 



