TEOPICAL FLORAS 63 



are found also in South America, and that about TOO are found 

 in the eastern portion from Venezuela to Brazil, so that prob- 

 ably not more than 500 reach the latter country. The com- 

 bined floras of Brazil and Central America, even as now 

 imperfectly loiown, will therefore reach about 34,300 species. 

 N^ow, considering how very rich the eastern slopes of the Andes 

 are known to be, and that the average width of the forest zone 

 between Brazil and the Andes is from 400 to 500 miles, while 

 the plateaux and western slopes also have a rich and distinct 

 flora and fauna, I think it will be admitted, that whatever the 

 combined floras of Brazil and Central America may amount 

 to, that number will be nearly or quite doubled when the entire 

 floras of Venezuela, the Guianas, Colombia, Ecuador, and Peru 

 are thoroughly explored. As, roughly speaking, Brazil con- 

 tains about half the great tropical forests of South America, 

 and allowing that its portion is the best kno^vn, we may fairly 

 add one-third of Spruce's lower estimate (25,000) to its 

 present numbers, Avhich will bring the whole to very nearly 

 40,000 sjDecies. By doubling this, we shall reach 80,000 as 

 the probable number of species existing in tropical South 

 America. 



As this number is considerably more than half the latest 

 estimate of the number of flowering plants yet known in the 

 whole world (136,000 species),^ more than half of which 

 number will be absorbed by the comparatively well-known tem- 

 perate floras, it will be apparent that we have at present a very 

 inadequate idea of the riches of the tropical regions in vege- 

 table life. This result will be further enforced by additional 

 facts to be adduced later. 



I will here give a table of the few known statistics for trop- 

 ical America, which, though very fragmentary, will serve to 

 show the basis on which the preceding estimate of probable 

 numbers rests. 



1 This number has been given me by Mr. W. B. Hemsley, Keeper of the 

 Kew Herbarium, as being that of Dr. Tlionner in 1008. 



