CLASSIFICATION. 33 
III. .spleniese=I ) orsal-fruited ferns, whose son, 
covered by scale- like indusia, are oblong or elongated 
in form, and spring from the sides of the veins. 
Iv. Blechneae=Dorsal-fruited ferns, -whose linear 
sori, covered by special indusia, are borne longitudinally 
between the midrib and margin of the divisions of the 
frond. 
v. Pterideae=Dorsal-fruited ferns, whose con- 
tinuous or interrupted aggregations of spore-cases are 
covered by the reflexed margin of the frond, altered 
in texture and becoming indusioid. 
* * Ring of spore-cases horizontal or oblique 
vL Hymenophylleae=^larginal"fruited ferns, 
whose spore-cases are clustered around veins (re- 
ceptacles) which project from the frond, and are sur- 
rounded by urn-shaped or two-valved involucres. 
H. OSMUNDACEJE=Ferns whose vernation is 
circinate and whose two-valved spore-cases have no 
elastic ring. 
III. OPHIOGLOSSACEJE=Ferns whose verna- 
tion is plicate, and whose two-valved spore-cases have no 
elastic ring. 
The distinguishing characters of the genera are the 
following : 
I. (i.)-Polypotlieoe. 
Sori circular, exposed 1. Polypodium. 
Sori circular, becoming confluent 
and concealed by the reflexed 
margins of the frond, unaltered in 
texture 2. Allosorus. 
Sori linear forked 3 . Gymnogramma. 
