450 GENERA OF FERNS. 
Ililust. Hook. et Bauer Gen. Fil. t. 31. Hook. et Grev. Ic. 
FAL t. 9. 
Obs. According to the description of authors, this and the 
following genus Hymenophyllum may be considered as form- 
ing a distinct natural group of about one hundred species, 
differing from most other ferns by their very delicate mem- 
braneous texture, as also by the apparent peculiar attach- 
ment of the sporangia, and direction of the ring. The spo- 
rangia being sessile, and closely seated round a columnar 
receptacle which is formed by a free prolongation of the 
venule, and either wholly included or much exserted beyond 
an urceolate or bilbabiate cystiform indusium, is a struc- 
ture analogous to other genera of Dicksoniee ; but what 
marks the present genera as peculiar, is, in the ring of the 
sporangia being more or less transverse or oblique to the 
point of attachment, which, if admitted as a character of 
primary importance, would be a reason for separating these 
genera from having any direct affinity with any tribe of ferns ; 
and which has been so done by several authors of eminence 
who have separated them from Polypodiacee, (as characterized 
with a vertical ring,) and forming of them the order Hy- 
menophyllee ; while again others place them in Gleicheniacee, 
with which they have no affinity except in the supposed ana- 
logous direction of the ring; but I am not inclined to 
consider the difference of structure of such importance as to 
justify their separation from true Polypodiacee ; for, according 
to my view, the peculiarity of the ring is to be accounted for 
by the sporangia being sessile and compactly seated round 
the columnar receptacle, in an imbricate manner, the pres- 
sure giving each sporangium a flattened form, their point of 
attachment being more or less excentric on the inner side or 
base, the upper edge of each inclining a little outwards, over 
which the ring passes, and therefore its direction appears to 
be more or less vertical, oblique, or transverse, according to 
the attachment and direction of the sporangia, and which is a 
structure quite analogous to the flattened sporangia of Also- 
phila, Cyathea, and other genera in which the sori are com- 
