ON GENERA AND SPECIES. 



I must state that after much study of this arrange- 

 ment I have not been able sufficiently to understand it to 

 make it practically useful. I do not clearly see what 

 object the author gains by introducing sectional names not 

 before used in the genus, more especially as these names 

 (Ccenopteris, Eupteris, Neuropteris, Doodya, Pleocnemia, &c.) 

 are apparently not given as special sectional names, but 

 used comparatively that is, all the species under Ccenop- 

 teris, Eupteris, &c., are presumed to have venation similar 

 to Ferns bearing those names. Therefore, in order to 

 ascertain the venation of one Fern, it is first necessary to 

 be acquainted with the venation of that with which it is 

 put in comparison. As, for example, to know Dictymia, it 

 is first necessary to be acquainted with the character of 

 the venation of Doodia and Pleocnemia. Unfortunately 

 too, the analogy in these two cases is far from obvious, the 

 genera in both cases being in every respect of quite dif- 

 ferent habits. I therefore see no good reason for making 

 such genera as Doodia and Pleocnemia types for arranging 

 other genera by venation. 



With regard to his arrangement of Phegopteris and 

 Aspidium, of which he enumerates in consecutive order 

 299 species thus viewing them as parts of a single genus 

 of these sixty-eight belong to the first part, Phegopteris ; 

 the remainder to the second part, Aspidium. I do not 

 consider it necessary to enter into further details. I will 

 only add that the sectional names are upon the same 

 principle as those of Polypodium, and that, in my opinion, 

 a simple generic name for groups of naturally allied 

 species, would render their study much easier than the 

 complicated comparative similitude with one another. 

 Mettenius has also published a memoir on the genus, 

 Asplenium and several other genera. 



