32 ON GENERA AND SPECIES. 



able number of new species, many of which appear to be 

 founded on very imperfect, and not well-authenticated 

 materials. A few of his new genera are admissible and 

 will be noticed in their respective places ; the greater 

 number, however, are untenable ; for instance, he describes 

 about fifty species of the genus Blechnum, of authors, which 

 he arranges under five genera, namely, Blechnum, Pardblecli- 

 num, Distaxia, Mesothema, and Blechnopsis ; the differential 

 character of these genera is, however, so slight that I do 

 not consider them worthy of adoption (see Blechnum). 



Another instance of creating genera on what may be 

 called fancied differences, is the genus Nipbobolus of Kaul- 

 fuss, of which Presl enumerates thirty-nine species arranged 

 under eight genera. On examining numerous sets of herb- 

 arium specimens said to be species of this genus, I find the 

 intermediate forms are so numerous that it is impossible to 

 collate them, so as to arrive at any satisfactory conclusion 

 as to what number of them are distinct species, for with all 

 the evidence that has come before me, I have not been able 

 to define more than about a third of the species recorded 

 by Presl, all of which I continue to retain under Niphobolus. 



Many other of Presl's genera have as little title to rank 

 as such as those of Blechnum and Niphobolus, and I deem it 

 best not even to notice them as synonyms, as it would only 

 add to the already overburdened Fern nomenclature. 



In the preface to this book it is shown that it is now 

 more than fifty years since the writer commenced to study 

 the collection of Ferns in the Eoyal Botanic Garden at 

 Kew, then amounting to about forty exotic species; and, 

 having had the opportunity of profiting by the verbal 

 observations of Robert Brown, who often directed my 

 attention to the mode of the arrangement of the veins 

 in different species of the genus Polypodium, as forming 



