ONE-SIDED FILMY FERN. 179 
in the One-sided than in the Tunbridge species; the 
_ pinne are always one-sided, being only half pinnate, and 
 eonyex above, while those of the Tunbridge are usually 
flat: the One-sided Filmy Fern has a more erect, the 
Tunbridge a more horizontal, and indeed a somewhat 
drooping, habit, so that on the trunk of a tree, the 
fronds seem to rest one on another, like the tiles of a 
: house. The involucre of the One-sided Filmy Fern 
is very different from that of the Tunbridge; it is 
elongate, swollen at the base, and its exterior edge 
perfectly even; when the seeds are mature it opens 
at the top, and, splitting down the middle, remains 
widely gaping. The reader is especially referred to 
the figures of these two delicate moss-like ferns, the 
smallest of all our species. 
‘The range of Unilaterale, as far as known in foreign 
countries, is coextensive with that of Tunbridgense ; 
two species are frequently found growing near 
each other. The range of this species in Great 
Britain appears to be more extensive than that of 
Tunbridgense: it also seems to be a more northern 
‘species, and generally to prefer a greater elevation 
and more exposed sites; still, as already stated, the 
plants are often found in close proximity, pat 
arly about the waterfalls in the neighbourhood of 
ey. In the Shetland Isles it grows in.one 
overhanging a subalpine stream near Ska, Unst, 
. lnxuriance and abundance. In the ae 
M 
