19 
GENERA. 
The rst order of tlie Ferns is conveniently divided into the sub -orders Nuclce 
and ndusiatce, according as the sori are naked or covered with an indusium. 
The arrangement of the species into 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 linear or oblong, scattered Grammitis. 
Sori round, scattered Polypodium. 
INDUSIATJE. 
Indusium distinct from the Frond. 
Sorus round. Indusium cleft into capillary segments . . 
Sorus round. Indusium cucullate or bladder-shaped . . 
Sorus round. Indusium peltate, either round or reniform 
Sorus linear or oblong, transverse, solitary. Indusium 
from lateral veins, opening towards the midrib 
Sorus linear, transverse, in twin masses. Indusia folding 
over each other, and opening outwardly 
Sorus linear, longitudinal, close to the midrib. Indusia ’ 
opening outwardly 
Woodsia. 
Cistopteris. 
Aspidium. 
Asplenium. 
SCOLOPENDRIUM. 
Blechnum. 
Cover part of the Frond itself reflexed. 
Sorus linear, continued around the margin of the frond Pteris. 
Sorus on transverse veins, near to the margin Cryptogramma. 
Sorus in distinct spots, attached to the cover itself Adiantum. 
Thecae in pitcher-shaped, one-valved receptacles Trichomanes. 
Thecae in compressed, two-valved receptacles Hymenophyllum. 
Thecae petioled, reticulated, terminating a leafy frond . . Osmunda. 
Thecae sessile, smooth, in a separate compound spike . . Botrychium. 
Thecae sessile, smooth, in a separate simple spike Ophioglossum. 
Thecae attached to the root, free, and indehiscent Pilularia. 
Thecae imbedded in the base of the leaves Isoetes. 
Thecae of two kinds, axillary in a leafy spike, or stem. . Lycopodium. 
Thecae of one kind, in catkins, terminating a leafless stem Eguisetum. 
