128 FILICES 
They are distinctly stalked, and serrated at the margins, a little spine sur- 
mounting each serrature. The under surface of the frond is of a delicate 
sea-green colour, with small, brown, chaffy scales about it. The upper sur- 
face is of a deeper hue, but not of a full green tint. The pinnules taper to 
a broad angled base, and are attached to the rachis of the pinne by a short 
and slender stalk. A very elegant variety, called P. subtripinndtum, has its 
pinnules at the base very deeply lobed ; and a form termed P. angustdtun 
has all its pinnules narrow and acute. 
7. BLADDER-FERN (Cystdépteris). 
1. Brittle Bladder-fern (C. fragilis). —Frond lanceolate, twice pinnate ; 
pinne lanceolate ; pinnules oblong, rather narrowed below, deeply pinnatifid ; 
segments sharply toothed or serrated. This fern, like all the other species 
of the genus, is fragile and delicate in texture, their membrane-like nature 
readily distinguishing the Bladder-ferns from most of our native plants. The 
beautiful little species called Brittle Bladder-fern varies very much in form 
and in some of its distinctive features, always, however, retaining its fragile 
nature. Its fronds, which are from five or six inches to a foot high, grow in 
tufts. The stalk is erect, slender, glossy, of a purplish-black colour, with a 
few scales at its base. The variable fronds may be generally described as 
lanceolate and twice pinnate, having in most specimens their pinnules pinna- 
tifid. Owing to their thin texture the veining is very apparent. From a 
somewhat winding mid-vein a lateral branch runs into each of the lobes; 
this again branches into smaller veins, almost every one of these bearing a 
cluster of capsules at about the middle of its length. ‘The cluster, which is. 
of roundish form, has a loose white membranaceous indusium, attached by 
its broad base at one side only, beneath the cluster. It soon tears into jagged 
segments, curling under at the part which is jagged, and finally disappears 
altogether. - The roundish form of the indusium in the genera Lastréa, 
Polystichum, and the Bladder-ferns, led earlier botanists to include them all 
in the Aspidium, or Shield-fern genus. In Cystépteris, however, the indusium 
is hooded, and not round and flat, and it is also sufficiently like a bladder to 
have given this name to the plants. The clusters of capsules are at first 
distinct, but they increase very rapidly, in some cases finally crowding into 
a mass. 
This fern is very widely distributed throughout the United Kingdom, 
preferring moist rocky places and walls in mountainous districts, and 
attaining the greatest luxuriance on limestone soils. It forms most beautiful 
patches of somewhat pale green verdure, springing from rocky crevices, its 
numerous fronds growing in tufts from its rhizome, and its black and wiry 
roots penetrating into the clefts. This plant has received much attention 
from botanists, as it has several forms or varieties, which are, however, inti- 
mately connected. That termed C. angustdta, which is the most distinct, is, 
however, by some writers on ferns, considered as a variety of C. dentdta. The 
frond in this variety is oblong-lanceolate, twice pinnate ; the pinnules linear 
lanceolate, more or less forming a wing, acutely pinnatifid or toothed. It is 
rather longer than the ordinary form, and tapers more towards the point of 
the frond, and also towards the points of the pinne. 
