TABLE OF BRITISH FERNS. 
13 
ing the spore-case, is the distinguishing peculiarity 
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 Trichomanineoe , without valves and bursting 
irregularly, but surrounded by urn-shaped involu¬ 
cres, the ring horizontal or oblique, complete. The 
second division has only one tribe or group : — 
Osmundinecz, spore-cases two-valved, opening verti¬ 
cally 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 Osmundinese. 
rOLYPODIACE^E. 
1.—PolypodinesD ; 2.—Trichomanincse; 3.—Osmun- 
dinese. 
P olypodines — fructification dorsal, that is, the 
spore-cases borne on the back of the frond. Com¬ 
prising the sub-groups Polypodiece , Gymnogrammece> 
Aspidiece , Aspleniece , Low,a,riecd or Plechnece , Pter- 
idece, Adiantece , Pystopteridece , Peranemece. 
Polypodies —Sori (or clusters of spore cases) round, 
and with no special indisum (or covering) : com¬ 
prising two genera— Polypodium Allosorus. 
