ON GENERA AND SPECIES. 58 
searches 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 
3 massed under one generic name, regardless of their dis- 
similar habits and anatomical structure. For instance, the 
dE Polypodium, 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 Polypodium trichomanoides, Swartz, and P. pectinatum, 
Linn., and others, rank with the large fronded genus 
Drynaria of Bory, and the large decompound subarbores- 
cent species of the section Phegopteris. This is consequent 
on all Ferns having round or oblong sori being placed 
. under the genus Polypodium. Upon such data, setting 
 &side habit, the Tree-Fern genus, Alsophila, R. Br., might be 
correctly referred to Polypodium. The same applies to 
Aspidium and Nephrodiwm, which, between them, contain 
227 species of very varied habit and venation. 
Then, again, all species with linear naked sori diverging 
from the mid-rib, whether on free or anastomosing veins, 
3 including the genus Selliguea of Blume, which differs from 
the whole of the Gymnogramma alliance*in having articu- - 
late venation. With regard to Acrostichum, 107 species ` 
j are deseribed, iui Fée and other authors have placed ` ` 
under fifteen genera, many presenting a very distinct habit — 
and of whatever habit of growth, are placed under Gymno- dd 
gramma, of which he enumerates seventy-four species, even SS 
