THE TUNBRIDGE FILM FERN. 303 
long, usually ovate, lanceolate-ovate, or oblong, more or less elon- 
gated, pinnate below. Pinn® or primary divisions alternate, 
decurrent so as to form everywhere, except at the base of the 
larger fronds, a narrow entire wing to the rachis; distichous, ascend- 
ing or sub-vertical, nearly rhomboid in circumscription, furcately 
bipinnatifid, that is to say, twice divided with the ramifications on a 
dichotomous or forked plan, the divisions alternating, and. so placed 
as to show an apparent excess of development on the anterior side 
caused, as may be seen, by the medial or axial vein, which may be 
recognised, curving upwards. Ultimate segments linear, obtuse, 
spinulosely serrate. 
Venation consisting of a series of dichotomous ramifications (two 
or three times repeated) of the wiry ribs which branch alternately 
from the main rachis, each ultimate segment having one of these 
divisions along its centre, and not quite reaching to its apex. Thus 
the fronds might be said to consist of slender branching wiry 
ribs everywhere bordered with a flat delieately cellular pellueid- 
membranaceous margin. 
- Fructification usually produced in the upper half of the fronds, 
extra-marginal, 7. e. the two valved involueres replace the lowest 
anterior segment, and are projected outwards from the margin, the 
opening being exterior. Sori consisting of numerous spore-cases 
clustered around the short receptacle, on which they are sessile. 
Receptacle formed of the altered apex of the vein (usually the lowest 
anterior vein of the pinna) spongy, oblong-clavate, free and central 
within the involucre, and shorter than its valves, therefore inclu- 
ded. Involucres sessile, supra-axillary 4. e. borne in the axils of the 
pinn or primary divisions, short, compressed, the base somewhat 
inflated, cuneate and more or less sunk in the segment, two-valved, 
the valves semiorbicular, flattish, spinulosely serrate at the upper 
margin. Spore-cases sessile, affixed obliquely, vertically compressed, 
thus lenticular, with a transverse ring. Spores minute, irregularly 
oblong, or triangular. In ordinary cases the lower anterior segment 
of each pinnæ only is fertile, but sometimes one or more others are 
also soriferous. 
Duration. The rhizome is perennial. The fronds are also per- 
ennial, growing up in the course of the summer, attaining their full 

