8 
PROCEEDINGS OF THE 
species disperse farther in an easterly or westerly direction 
than towards the Equator. 
Now if we compare the genera of the above mentioned 
Floras or countries, we shall find that they (viz. genera) have 
a wider range than species : that is, are more extensively 
dispersed over the earth ; that in remote regions there are 
many more common genera than common species, and in 
contiguous countries that the genera bear to each other a 
much higher proportion than the species. The number of 
-British genera of vascular plants is four hundred and sixty; 
of these four hundred, or five-sixths of the whole are the pro- 
duce of the country round London, limited as above. And 
taking the London species at one thousand, and the British 
at one thousand five hundred, we find that the species in- 
crease as 2 : 3, and the genera as 5 : 6 only. 
The Austrian Flora of Host, which may be taken as a 
mean proportional, both in number of species and range of 
temperature, between the German and French Floras, com- 
prises about three thousand three hundred species, and seven 
hundred genera; amongst which almost every British genus 
and species will be found. Hence we perceive that the Bri- 
tish and Austrian species are to each other as 15 : 33, and 
the genera as 23 : 35 ; or fewer than one half of the British 
species are found in Austria. But about two-thirds of the 
genera. The number of genera common to Britain and 
India, according to the Indian Flora above mentioned, is 
about one hundred and twenty, although the common spe- 
cies hardly amount to thirty. The proportion of genera to 
species being as 4 : 1. 
From these statements, the following consequences may 
be legitimately deduced, viz. : that a person well acquainted 
with British plants, or even with those found in the London 
district, will readily recognize almost all the plants of Lap- 
land and Sweden, above one-half of the German species, 
one-third of the Austrian, and one-fourth of the French. 
And as genera are more extensively dispersed than species, 
the London Botanist, by knowing the plants of his own 
district, can refer to their proper genera one thousand three 
hundred British species, about two thousand five hundred 
Austrian, and three thousand French species. 
From similar data it can be shown that about two thou- 
sand species of the Equinoctial plants of America are re- 
ferable to their proper genera by British Botanists, and also 
that the generic characters of three thousand Hindustani 
