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 farther 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 

 of Lindscea, and more especially as it is soon obliterated by 

 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 Pteris aquilina. 

 In this the sporangia are seated as it were in a slit, similar 

 to that of Lindscea, 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 Pcesia, which Mr. Moore adopts, 

 and places it in his section Dicksoniece, next to Cibotium, but 

 with which it has no natural affinity, and cannot be well 

 separated from Pteris. 



* Sarmentum thick, fleshy, hypogeous. 

 Sp. 0. aquilina (Linn.) ; O.caudata (Linn.) j 0. esculenta 

 (Forst.) 



