158 
ONE-SIDED FILM FERN. 
alternately from the rachis, forking again so as to ex- 
tend a vennle to each segment ; and after leaving the 
midrib are furnished with a narrow membranous leafy 
wing or border (which the rib itself has not). The 
sori are collected round the free ends of the veins and 
contained in the urn-shaped covers or involucres, 
which differ from those of H. Tunbridgense in being 
more or less obviously stalked instead of sessile, and 
in having their valves entire instead of serrated at 
the upper margin. Mr. Clowes notices also a farther 
difference between the species : that the fronds of H. 
Tunbridgense are annual, “ never grow more than one 
year;” while those of H. unilaterale are perennial, 
lasting for several years and annually renewing their 
growth, bearing spores year after year. 
HABITATS. 
Patterdale, Ambleside (J. Bowerbank) ; Stock Gill 
( Miss Beever ) ; Dungeon Gill, Scafell, (Black Rocks 
and Great End), Bowfell, Ennerdale (Dr. Dickinson) ; 
Scale Force ( E . C. Watson ) ; Honister Crag (Bev. G. 
Binder) ; Gatesgarth Dale, Borrowdale, Lodore (Miss 
Wright) ; Keswick, near Hawkshead (Miss S. Cow- 
burn) ; Coniston Old Man, Silverdale (Miss Beever) ; 
Dalegarth (Bob son) ; High Stile (Binder). 
