CHARACTERS OF TRIBES AND GENERA. 327 



186. ATHTRIUM, Both. (1788). 



Allantodia sp., E. Br., 1810 ; Asplenium sp. auct., sect. Atliy- 

 rium, Hook. Sp. Fil., J. Sm. Ferns Brit, and For. 



Vernation fasciculate, erect or decumbent, solitary or 

 becoming caespitose. Fronds bi-tripinnatifid, 1 to 4 feet 

 high, ultimate segments dentate, or deeply laciniated. Veins 

 forked ; venules free. Sporangia unilateral, or often bi- 

 lateral on the lower exterior venule. Indusium generally 

 vaulted, single or binate, or oblong reniforme, forming 

 linear, straight, or curved, generally unequal-sided sori. 



Type. Asplenium Filix-foemina, Bernh. 



Illust. Hook, and Bauer. Gen. Fil., t. 16 ; Moore Ind. 

 Fil., p. 37, A. ; Hook. Syn. Fil., t. 4, fig. 38, E. 



OBS. The form of the sori in the species included in this 

 genus is very variable, some being unilateral as in Asple- 

 nium, others binate as in Diplazium, while in others the 

 iiidusium is oblong reniform as in Fadyenia, but the lobes 

 are generally unequal, such differences being in many 

 instances found in the same frond. In many the indusium 

 is cylindrical and vaulted like that of true Allantodia. 



In the " Species Filicum," as well as in " Ferns, British 

 and Foreign," Athyrium is ranked as a section of Asplenium, 

 but, for the sake of a more natural grouping of species, I 

 deem it best to allow it to rank as a genus ; more distin- 

 guished by its habit of growth and the soft and brittle 

 nature, and highly compound character of the fronds, than 

 by the character of the sori ; and the species may be viewed 

 as having more relationship with the compound-fronded- 

 species of Diplazium than with Asplenium. 



In the " Species Filicum " twenty-nine species are enu- 

 merated, but in the " Synopsis " the number is reduced to 

 nineteen, ten of which have come under my observation in 



