TIIK Tl'NimilKiK FILM FERN. 



Vernation circulate. 



Frond* smooth, pel lucid -mem bra naceous, minutely cellular, dcep-olivc or sometimes brightish green, 

 from one to four or live inches long, varying in outline, usually ovate, lanceolate-ovate, or oblong, more 

 or less elongated, pinnate below, f'intuv or primary divisions alternate, decurrent so as to form 

 everywhere, except at the base of the larger fronds, a narrow entire wing (o the rachi* ; distichous, 

 ascending or sub-vertical, subrhomboid in circumscription ; fureatuly bipinnatiiid, that is to say, twico 

 divided with the ramifications on a dichotomouft or forked plan, the divisions alternating, and so placed 

 as to show an apparent excess of development on the anterior side from the medial or axial vein (which 

 may be recognised), curving upwards. Ultimate segments linear-obtuse, spinuloscly serrate. 



Venation consisting of a series of dichotomous ramifications (two or three-times repented) of the 

 wiry ribs which branch alternately from the main rachis, each ultimate segment having one of these 

 divisions along its centre, ami not quite reaching to its apex. Thus the fronds might be said to 

 consist of slender branching wirv ribs everywhere; bordered with a delicately cellular pcllucid- 

 membranaceons margiu. 



Fructification usually produced in the upper half of the fronds, extra-marginal, u *\ the two valved 

 involucres are projected outwards from the margin, the opening being exterior. Sort consisting of 

 sessile sporc-e^scs, clustered around the receptacle. JtcwptacU formed of the altered apex of the 

 lowest anterior vein of the pinna, spongy, oblong^clavate ; free, central and shorter than the valves of tho 

 involucre, therefore included. Involucres sessile, supra -axillary, i A borne in the axils of tho pinmu or 

 primary divisions, short, compressed, the base somewhat inflated, cuncate and more or less sunk in tho 

 segment ; the anterior part two-valved, the valves scmiorbicular, flattish, Kpinulosely serrate at the upper 

 margin, fiporc-caics sessile, affixed obliquely, vertically compressed, thus lenticular, with a transverse 

 ring. Spores minute, irregularly oblong, or triangular. Normally the lower anterior branch of the 

 pinme only is fertile, but sometimes one or more others are also soriferous. 



Duration, Tho rhizome is perennial. The fronds arc also perennial, growing up in the course of 

 the summer, attaining their full growth during the season, but enduring two or three years under 

 favourable circumstances. 



The two British ffi/menophyUums, may bo known from other Ferns by the matted growth of their 

 thread-like rhizomes, by the small size, the pellucid, and finely cellular texture of their fronds, whose 

 segments have each only a central rib, and by tho two-valved marginal fructifications. They may be 

 best known from each other by the form of tho involucres and of their valves ; for although they may 

 probably always be recognised by a practised eye by their peculiarities of growth, yet these latter are 

 not features to be generally depended on. In //. tunbridff&w the valves of the involucre arc roundish 

 and flattish, and the upper margin is spinulosely-serrate, like the margin of the segments of the pinna; ; 

 whilst in //. unitaterate tho valves are ovate and convex, and the margin is quite even* In the former 

 the involucres arc usually sessile and erect ; in the latter stalked and deflcxed in an opposite direction 

 to the segments. No varieties of importance have been observed in the British Sym&xophyUum*. 



