60 8 



The forms of these 14 species occurring in Andes-West-Indian islands and 

 South Brazil respectively are, however, very rarely quite uniform, but, on the other 

 hand, not so different that they can be separated from each other as species. Thus 

 a pronounced dilTerence between the fern-flora of the two regions is clearly seen, 

 but there is also a distinct resemblance, indicating that the whole tropical American 

 flora was in earlier periods not so specialized as in recent times. This resemblance 

 is shown mainly thereby that each of the two regions is inhabited by a long series 

 of species, which are, in the other region, superseded by other, but closely related 

 species. This circumstance can mean that the floristic separation of the two re- 

 gions took place so long ago, that the species, which were originally common to 

 both regions, have had time to be segregated into several daughter-species, but, 

 on the other hand, the segregation is till now not so far proceeded that separate 

 genera or groups of specially characterized species could have been developed. In 

 every case, such a specialization is in first beginning. 



277 species out of the 280 are found in America only. Two, D. mollis and 

 D. goiniylodes, are cosmopolitic within the tropics and subtropics, and one, D. 

 eriocoiilis from Brazil, is not specifically distinct from the West-African D. ciirhosa. 

 It is possible that some others of the South-Brazilian species occur also in tropical 

 West-Africa. 



