Sadler, in his enumeration of true Ferns, assigns 1508 species 

 to the whole world, sixty-seven to Europe, and thirty-six to 

 Britain ; we have, therefore, but ^ part of the entire number. 

 Supposing that the 1508 species were arranged in the most unex- 

 ceptionable manner, all their characters carefully investigated, 

 and their position in some system fixed in strict accordance with 

 those characters, there still must exist many a gap between 

 species and species, or how could those numerous ferns still un- 

 discovered be hereafter admitted into the arrangement ? Granting, 

 then, the imperfection of any arrangement, however numerous 

 the species it may embrace, how can we hope to arrive at any- 

 thing approaching a continuous series, when our materials can 

 scarcely be supposed to reach ^]^ part of the entire number ? 

 How idle would it be to expect that in our mere handful of 

 Ferns, each should approach another by that gentle gradation 

 which would indicate the existence of a connected and harmonious 

 whole? Fully impressed with the difficulty of the case, I 

 am by no means disposed to complain of errors in the arrange- 

 ments of those authors who have preceded me, neither have I 

 any argument to adduce in favour of my own. 



It is curious to remark how each character by which Ferns 

 have been distinguished has yielded to a new and more precise 

 one. Sir J. E. Smith observes that Ray, Tournefort, Plumier, 



