448 M. A. DeCandolle on the Characters which distinguish 



It will be seen that if we regard tlie numbers of the Flora of 

 Maine-et-Loire as unity, the augmentations are — 



For the surfaces . . . = 1 



For the species . . . =: 1 



For the genera . . . = 1 



For the famihes . . , = 1 



Maine-et- Centre of 



Loire. France, France. 



7-14 : 73 



1-17 : 2-77 



113 : 1-56 



1-02 : 116 



Calculating then by the square league, we shall obtain for 



one league — 



Species. Genera. Families. 



Maine-et.Loire ... 36 1-3 0-24 



Centre of France ... 05 02 0-03 



France 0-17 004 002 



Lastly, the proportion of the species to the genus and family 

 is — 



Maine-et-Loire . 

 Centre of France . 

 France .... 



For each of the fourteen districts of Silesia the number of 

 species to the genus varies betweeen 2*1 and 2-3, and the num- 

 ber of species to the family between 8*2 and 10- 1 ; but for the 

 whole of Silesia the numbers are 2*8 species to each genus and 

 14-4 to each fiimily (Schneider, die Verth. &c. p. 210), and for 

 the whole of Germany they are 4'2 and 19 (Koch). 



I might multiply these examples, but a more general fact 

 will be sufficient for the most complete demonstration. Of 

 course the terrestrial globe is the largest region that we can 

 take into consideration ; its surface, deducting the parts covered 

 by water, is 6,825,000 leagues; and if we suppose that there 

 are 200,000 phanerogamous plants, which is one of the highest 

 estimates that has ever been proposed, there would be for each 

 square league 0029 species, or say 0-03. Now the most 

 restricted and even the poorest localities have an infinitely 

 greater number of species to the square league. Thus, at the 

 summit of the Pic du Midi de Bagneres, there are 71 phanero- 

 gamous plants upon a surface of 200 metres (Ramond) ; in 

 Scotland, on the most monotonous peaty plains, there are from 

 50 to 100 Phanerogamia in a square English mile; and in the 

 environs of London, which do not possess a great abundance of 

 spontaneous plants, 400 species have been counted in a square 

 mile (Watson, Phytol. 1838, p. 267). 



In the entire vegetable kingdom, that is to say, for the whole 

 surface of the earth, there are about 12 species to each genus 



