292 VIEWS, &C. PHYSIOGNOMY OF PLANTS. 



systems is however deceptive, and only apparently con- 

 siderable ; for the quotient of this family (which within the 

 tropical zone is T y, in the temperate zone ■£-, and in the 

 frigid zone ^) shows that more species of Compositse than 

 of Leguniinosse have hitherto eluded the diligent research 

 of travellers ; for even when multiplied by 12 we only obtain 

 the improbably small number of 144,000 for the sum total of 

 the Phanerogamia ! The families of the Grasses and of the 

 Cyperacese give still lower results, because a proportionally 

 smaller number of species have been described and collected. 

 We need only cast a glance at the map of South America, and 

 remember that the vast extent of country occupied by the 

 grassy plains of Venezuela the Apure and the Meta, as well as 

 to the south of the woody region of the Amazon, in Chaco, in 

 Eastern Tucuman, and in the Pampas of Buenos Ay res and 

 Patagonia, has either been very imperfectly or not at all 

 explored in relation to botany. Northern and Central Asia 

 present an almost equally extensive territory occupied by 

 steppes ; but here a larger proportion cf dicotyledonous plants 

 is intermixed with the Gramineas. If we had sufficient 

 grounds for believing that one-half of all the phanerogamic 

 plants existing on the surface of the earth are known, and 

 if we estimate this number at only 160,000 or at 213,000 

 known species ; we must give to the family of grasses, whose 

 general ratio appears to be -jL-, in the former case at least 

 26,000, and in the latter 35,000 different species, of which in 

 the first case -f-, and in the second ^ are known. 



The following considerations oppose the hypothesis that we 

 are already acquainted with half the Phanerogamia on the 

 earth's surface. Several thousand species of Monocotyledons 

 and Dicotyledons, and among them lofty arborescent forms, 

 have recently been discovered (I would remind the reader 

 of my own expedition) in districts of a very large extent, 

 which had already been explored by distinguished bota- 

 nists. Yet that portion of the great continents which has 

 never been visited by botanical observers far exceeds the 

 extent of the parts even superficially traversed. The greatest 

 variety of phanerogamic vegetation, i. e. the greatest number 

 of species on an equal area, is to be met with in the tropical 

 or sub -tropical zones. It is therefore the more important to 

 bear in mind that we are almost wholly unacquainted, north of 



