382 GEOGRAPHICAL DISTRIBUTION. 
species are enumerated as belonging to this region, 
of which 477 are peculiar. 
10. Tropical America. This region contains 946 species, 
of which 708 are peculiar, thus showing that this 
ise the preceding are the two richest regions in 
Ferns, 
The above is sufficient to give a general view of the dis- 
tribution of the Fern flora over the earth. 
With regard to the greater or lesser number of allied 
species common to any district, Mr. Baker says, “The ` 
remarkable point about the distribution of Ferns is, that 
there is so little trace amongst them of the concentration 
of allied forms in the same district.” 
There can be no doubt that this view is consequent on 
the character of the fructification being made the bond of 
union of species, by which large unnatural genera are 
formed as in the “Species Filicum,” which I have already 
commented upon ; but on breaking up these large genera 
we obtain smaller genera of a few or many naturally allied 
species, which in many instances may be termed geogra- 
phical genera, and which coincides with Mr. Darwin’s 
view on the distribution of plants generally, for he says 
that, *Some few families, many sub-families, very many 
genera, and a still greater number of sections of genera, 
are confined to a single region, and it has been observed by ` 
several naturalists, that the most natural genera in which ` ` 
the species are most closely allied to one another are t ger 
rally local or confined to one area,” 
In support of this may be mentioned the genera Nipho. — S 
bolus, Drynaria, great part of Phymatodes, Platycerium, and : SE 
Thamnopteris, which have their head-quarters in the regions ; 5 a 
of the East, and by restricting Davallia, as I do, to tho 
species with articulate vernation, all belong to the € E 
