II. UNCERTAINTY OF SPECIES. 43 



studied the descriptive works relating to the same species 

 of plants in adjacent countries. Yet the books of this 

 Botanist show much uncertainty and variability. And 

 by the instance of the Dryas before adverted to, on page 

 38, we may see that the uncertainty can be extended to 

 one of the oldest and most widely recognized species, by 

 splitting it most unequally in twain. 



A second example of an Author widely at variance with 

 himself on species, may be taken from a work devoted 

 exclusively to the Ferns of Britain. The beautifully 

 illustrated ' History of British Ferns ' by Mr. Newman, 

 has had three editions, dated in 1840, 1844, 1854. These 

 editions differ remarkably in the number of species de- 

 scribed in them as distinct, namely, 33, 40, 50 species, — 

 plus also some demi- species to increase the latter high 

 number. Yet during the interval of 1840 — 1854 scarcely 

 half a dozen actual novelties were added to the lists of 

 British ferns ; the changes of number being otherwise 

 induced by subdividing some of the species of the earlier 

 editions into two or more species of the later editions. 



With reference to the former remarks on generic 

 groups, page 18, it seems to be further deserving of note 

 here, while attending to Mr. Newman's botanical writings, 

 that the number of genera also has a corresponding 

 increase in them. The 33 species of the first edition 

 were arranged under or into 18 genera ; and in the thii'd 

 edition the same species are divided among 23 genera. 

 It would thus seem to be a fair inference from the prac- 

 tice, of our best Pteridologist, that the genera of ferns are 

 also in some degree conventional or optional, equally 

 with the species. The fact is so ; but simply because 

 sometimes one character, sometimes another character, is 

 arbitrarily adopted as a distinctive test of a genus, ac- 

 cording to the whim of the individual writer. To revert 



