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 

 and 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 gene- 

 rally local or confined to one area." 



In support of this may be mentioned the genera NipTio- 

 T}olus^ Drynaria, great part of Phymatodes, Platy cerium, and 

 Thamnopteris, which have their head-quarters in the regions 

 of the East, and by restricting Davallia, as I do, to the 

 species with articulate vernation, all belong to the Eastern 



