Natural Orders .] 
APPENDIX. 
585 
involucrum originates from the inner branch of a primary vein, which 
is usually the case, it opens inwards or towards the mid-rib of the frond 
from which the vein is derived ; and that when it arises from the lower or 
outer branch of a vein it opens outwards, or in an opposite direction, in- 
stances of which occur in several species of the genus, in some of those espe- 
cially w here the frond is simple. On the same law also depends the peculiar 
character of Scolopendrium, in wdiich the involucra are produced in pairs, 
one of each pair originating from the lower branch of a vein, the other from 
the upper branch of the vein immediately below it ; they consequently open 
pi opposite directions and towards each other. This law, however, in Asple- 
nium is only observed where the vein has but few branches, for when these 
are more numerous, and especially when, in consequence of their greater 
number, the vein has amanifest trunk or axis, the involucra of all its branches 
open towards this axis : the most remarkable instances ofthis occur in those 
species of the genus which authors have separated from it, under the name 
ofDiplazium, where, liow-ever, another peculiarity exists, depending on the 
same law. This peculiarity consists in the inner branch of the vein, or that 
adjoining the mid-rib, appearing to have a relation not only to the axis of 
the vein but to that of the pinna or frond from which the vein originates; a 
relation indicated by its having two involucra, one of which bursts towards 
the axis of the vein, the other towards the adjoining mid-rib. This double in- 
volucrum constitutes the character ofDiplazium, but as it is confined to the 
inner branch, all the others being simple, and opening towards the axis ofthe 
vein, there do not appear to be sufficient grounds for its separation from 
Asplenium. I consider the curved involucrum of Asplenium Filix Foemina, 
which exists only on this inner branch ofthe vein, as somewhat analogous 
to the double involucrum of Diplazium ;.but in another point of view it may 
be regarded as an approach to the structure of Nephrodium, to which this 
plant has been improperly referred. 
von. n. 
4 F 
