GENERA. 
The first order of the Ferns is conveniently divided into the suborders 
Nudce and Indusiatce, according as their sori arc naked or covered with an 
indusium. Their arrangement into Tribes and Genera depends upon the 
shape and position of the Sori, together with the nature, the adherence, and 
the manner of opening of the indusium when there is one. In the other 
orders the same principles are adopted, as far as their structure will admit. 
As the orders of the Fern Allies contain each but one British genus, the 
characters of that genus are but a recapitulation of those of the order itself. 
NUDJE. 
Sori round, scattered Ploypodium. 
Sori linear or oblong, scattered Grammitis. 
INDUS I AT M. 
Indusium distinct from the Frond. 
Sorus round. Indusium cucullate or bladder-shaped Cistofteris. 
Sorus round. Indusium cleft into capillary segments . . Woodsia. 
Sorus round. Indusium peltate, either round or reniform Asfidium. 
Sorus linear or oblong, transverse, solitary. Indusium ) 
from lateral veins opening towards the midrib I Asplenium. 
Sorus linear, transverse, in twin masses. 5 Indusia > Q 
folding over each other, and opening outwardly $ Scolofendrium. 
Sorus linear, longitudinal, close to the midrib. Indusium ) T1 
opening outwardly ^ Blechnum. 
Cover part of the Frond itself reflexed, 
Sorus linear, continued around the margin of the frond Fteris. 
Sorus on transverse veins, near to the margin Cryttogramma. 
Sorus in distinct spots, attached to the cover itself. . . Adiantum. 
Theca: in pitcher-shaped, one valved receptacles Trichomanes. 
Theca: in compressed, two valved receptacles Hymenophyllum 
Theca: petioled, reticulated, terminating a leafy frond. . Osmunda. 
Theca: sessile, smooth, in a separate compound spike Botrychium. 
1 heca: sessile, smooth, in a separate simple spike . . OrnioGLossuM. 
Theca: attached to the root, free, and indehiscent Pilularia. 
Thecae imbedded in the base of the leaves Isoetes. 
I lieea: of two kinds, axillary in a leafy spike, or stem. . Lycotodium. 
( heca: of one kind, in catkins, 1 ermine ting a leafless si cm Equisf.tv m 
