298 -CHARACTERS OF TRIBES AND GENERA. 
Pteris aquilina marks it as a type of a small group, distinct 
from the preceding genus, and as such it is further distin- 
guished by the presence of what is supposed to be an 
interior indusium, of which the author of the “ Species 
Filicum " says, “ Easily as the outer involucre of Pteris 
aquilina is to be seen, even with the naked eye, the inner 
one, except in a peculiar state of the sorus (before it is 
mature) can only be brought to view by careful dissection 
under the microscope. I have, however, satisfied myself 
of its existence, though I have often failed to detect it; 
indeed the fact appears to be ignored by the most distin- 
guished writers on Ferns.” My observation on this point 
is, that there is to be seen in the early stage of the sorus, — 
rising from the interior side of the receptacle, a narrow, 
thin, elevated fimbriate ridge, but which in my opinion 
cannot be considered a special indusium analogous to that ud 
of Lindsea, and more especially as it is soon obliterated by 7 
the growth of the sorus. However, a more evident interior 
indusium is to be seen in Pteris glutinosa, a Fern of special ` ` 
habit, having alternately branched decompound fronds, ` 
agreeing in general mode of growth with Pieris aquilina. a 
In this the sporangia are seated as it were in a slit, similar ` 
to that of Lindsæa, but, although such is the case, I cannot = 
view the interior lobe of the slit otherwise than as a 
thickened lamina. It is, however, a specially marked cha- 
racter, and it is supposed to be the Fern described by St. 
. Hilaire under the name of Pesia, which Mr. Moore adopts, ` 
and places it in his section Dicksoniew, next to Cibotium, but 
. With which it has no natural affinity, and cannot be well ` 
separated from Pteris, | 
* Sarmentum thick, fleshy, hypogeous. a 
Sp. O. aquilina (Linn.) ; O.candata (Linz.) ; O. esculenta | 
(Forst.) : 
