ON GENERA AND SPECIES. 53 



searclics of future writers, and which ought therefore to be 

 gratefully acknowledged ; a middle course has been 

 pursued between the highly multiplied genera of Presl and 

 J. Smith, and the too meagre enumerations of Willdenow, 

 Sprengel, Link, Kunze, and others." 



By adopting the above view, hundreds of species become 

 massed under one generic name, regardless of their dis- 

 similar habits and anatomical structure. For instance, tlie 

 genus Polypod'ium, as characterised in the " Species Fili- 

 cum," contains 407 species, amongst which are found the 

 greatest diversity of size and mode of growth, as also in 

 anatomical structure. The small grass-like species cha- 

 racterised by Swartz and others under the genus Gram- 

 mitis, and the many small pinnatifid species represented 

 by Pohjpndimn tricliomanoides, Swartz, and P. fectinaimn^ 

 Linn., and others, rank with the largo fronded genus 

 Drynaria of Bory, and the large decompound subarbores- 

 cent species of the section Fhegopteris. This is consequent 

 on all Ferns having round or oblong sori being placed 

 under the genus Polypodmm. Upon such data, setting 

 aside habit, the Tree-Fern genus, Alsophila, R. Br., mig-ht be 

 coi-rectly referred to Polypodmm. The same applies to 

 Aspidium and Neplirodiuin, which, between them, contain 

 227 species of very varied habit and venation. 



Then, again, all species with linear naked sori diverg-ing 

 from the mid-rib, whether on free or anastomosing veins, 

 and of whatever habit of growth, are placed under Gyinno- 

 gramma, of which he enumerates seventy-four species, even 

 including the genus SelUguea of Blume, which differs from 

 the whole of the Gymnograrmna alliance in having articu- 

 late venation. With regard to Aarostichum, 1C7 species 

 are described, which Fee and other authors have placed 

 under fifteen genera, many presenting a very distinct habit 



