4 PREFACE. 



of years to the preparation and publication of the " Species Filicum " and 

 other works on the same subject, the Author feels satisfied that these 

 doubtful and imperfectly described species form the greatest obstacle to 

 any satisfactory advance in descriptive Pteridology.* He in ay, indeed, point 

 with satisfaction to the fact, that before he undertook his work their 

 number was many times greater than that still cumbering the volumes. But 

 there is little satisfaction in the reflection that for the identification of a 

 great majority the Author is indebted more to some happy accident, to the 

 possession of copious and varying suites of specimens, or to circumstances 

 tfoaiiacted with fcfiti {ri$tory or locality of the species, than to their published 

 descriptions^ or to v scientific evidence. 



: ; ' s jljdt^ hav^bfteta l iW t fruitful sources of these " bad species" : the first, 

 the idea that geographical limits must limit the dispersion of species ; the 

 second, that any single characteristic, however minute, if only either con- 

 stant or prevalent in a given area, is of specific value. Such arbitrary 

 conclusions have led to the well-known Osmunda regalis receiving different 

 names in many different countries, and to the forms of our Aspidium 

 (Polystichum} aculeatum having even more names in our own country, and 

 still others in exotic regions. The errors arising from the first are corrected 

 as rapidly as botanical and geographical discoveries advance together ; but 

 it is not so with those due to the second source, for the difficulty of limiting 

 these variable species is so great, that it often becomes impossible to frame 

 such diagnoses as shall include all the varieties of one species, and exclude 

 the varieties of another closely allied species. In all these cases we must 

 trust to time and experience to test our conclusions ; and such difficulties 

 should teach us to look with indulgence on the views of those who differ in 

 opinion from ourselves. 



The same remarks apply to the genera as to the species of Ferns ; the 

 former having been, in the Author's opinion, unnecessarily multiplied. It 



* In connection with Fern history, Mr. Thomas Moore undertook the publication of 

 an extremely useful work under the title of " Index Filicum," to consist of a Synopsis, 

 with characters of the genera, and an enumeration of the species of Ferns, with 

 synonyms, references, &c. &c., accompanied by excellent outline figures of the genera. 

 It is compiled with great industry and ability, and enumerates in an alphabetical 

 arrangement of the genera, from A crophorus to Goniopldebium inclusive, 1,730 species of 

 true Ferns. The list of synonyms, both of genera and species, shows at a glance how 

 much Pteridologists have been at variance on these points. The species enumerated 

 in our "Species Filicum" amount to 2,401 ; according to Mr. Moore, the number of 

 known Ferns would be 2,782. 



