TABLE OF BRITISH FERNS. 
13 
rounding the spore-case, is the distinguished pecu- 
liarity of the True Ferns. Polypodiacese are divided 
into those whose spore-cases are without valves and 
those which are two-valved. In the first division 
are two tribes or groups : — Polypodinece, without 
valves, bursting by an irregular and transverse cleft, 
the elastic ring vertical and nearly complete ; and 
Trichomanines , without valves ; and bursting irregu- 
larly, but surrounded by urn- shaped involucres, the 
ring horizontal or oblique, complete. The second 
division has only one tribe, or group : — Osmundines, 
spore-cases two-valved, opening vertically or at the 
top, the ring merely rudimentary. 
Ophioglossaces are Ferns whose young fronds are 
folded up straight , and whose spore- cases have no 
ring. They are two-valved like the Osmundineae. 
POLYPODI ACE.ZE . 
1 . — Polypodineas ; 2. — Trichomaninese ; 3. — Osmun- 
dineae. 
Polypodineae — fructification dorsal, that is, the 
spore-cases borne on the back of the frond. Com- 
prising the sub-groups Polypodies, Gym, nogrammes, 
Aspidies, Asplenies, Lomaries or Blechnes, Pter- 
ides, Adiantes, Dystopterides, Peranemes. 
Polypodies — Sori (or clusters of spore-cases) round, 
and with no special indusium (or covering) : compris- 
ing two genera — Poly podium, Allosorus. 
