21 . 
THE BRITTLE BLADDER FERN. 
C ystopteris frajilis. 
Plate 5, Fig. 4, Page 225. 
A small but very beautiful group is formed by our British 
Bladder Ferns. The common name is neither euphonious 
nor poetical, and the botanical name is but a literal rendering 
of its English designation. The word c.y stop ter is, in fact, 
comes from two Greek words, Icystos, a bladder, and pteris, 
a Fern. Frcigilis translates itself, and as applied to the 
present species, refers to the brittle, or fragile, and peculiarly 
herbaceous nature of the fronds of this little plant. The 
generic name has reference to the peculiar character of the 
indusia or coverings of the spore cases. In the Cystopteri* 
group these organs, which are roundish in shape, are raised 
over the sori in the form of hoods or bladders. Hence the 
name of the genus, which, however, was formerly, in company 
with the two genera of Polystiehum and Lastrea, included 
under the genus Aspidiuvi. C ystopteris frag il in may be 
described as a rock-loving Fern, its favourite habitats being 
the moist and shady clefts and crevices of limestone rocks, 
but it is sometimes found growing on buildings, such as 
church and garden walls. 
Description. — The rootstock of this beautiful Fern is 
tufted, having fibrous rootlets, the crown being composed of 
a little nest of incipient or unrolled fronds, from six inches 
