75 



et scq., of which the limits of the present work will not admit an 

 extract. 



In the durability of the fronds for several successive years, in 

 general habit and texture, Trichomanes has all the characters of a 

 tropical species, and though naturalized in our sister island, under 

 the influence of a very moist and temperate climate, would pro- 

 bably not bear exposure even in corresponding localities in Eng- 

 land, where the winters are so much more severe, and the drying 

 effects of the easterly winds in the spring so generally prejudicial 

 to vegetation. 



Genus 15. HYMENOPHYLLUM. 



GEN. CHAR. Sori marginal. Thecse sessile on a columnar sub- 

 clavate receptacle within a two-valved involucre of the same 

 texture as the frond. 



The name, from v/j,r)v, a film or membrane, and (frvXXov, a leaf, 

 is expressive of the pellucid filmy texture of the frond. The genus 

 formed a part of the Linnsean Trichomanes, but was separated by 

 Sir J. E. Smith, in consequence of the bivalvular involucre and 

 short receptacle. The division is rather one of convenience than 

 admissible on a structural foundation. The two British species 

 carry a fragility of form and t.exture almost exclusively charac- 

 teristic of the smaller species of tropical ferns, to the highest lati- 

 tudes in which it seems capable of existing. 



HYMENOPHYLLUM TUNBRIDGENSE. Tunbridge or Common Film 

 Fern. TAB. XLIL 



Fronds membranaceous, pinnate : pinnse distichous, pinnatifid, 

 decurrent, forming a broad wing on each side of the rachis ; the 

 segments linear, undivided or bifid, spinosely serrated. Involucre 

 solitary, axillary, suborbicular, compressed; the valves spinosely 

 serrated. 



Hymenophyllum Tunbridgense, Smith. E. B. 162. Hooker and 

 Arnott. Babington. Moore. Newman. Trichomanes Tun- 

 bridgense, Linnceus. 



Abundantly distributed in the north-western and southern coun- 

 ties of England, in mountainous and rocky districts ; in Wales ; 

 and less frequently in the Highlands of Scotland, and in Ireland ; 

 growing on shady wet rocks, and among moss on the trunks and 

 roots of old trees, or on the ground near lakes and rivulets. The 

 black and thread-like rhizoma spreads and branches widely, form- 

 ing a kind of turf over the surface on which it grows, and from 

 ' . * K2 



