106 HISTORY OF BRITISH FERNS.
C ystopteris fr a g il is , Bernhardi.—The Brittle Bladder-
Eern. (Plate X. fig. 1.)
This is a tufted-growing plant, spreading, if undisturbed
under congenial circumstances, into large patches of numerous
crowns, each of which throws up a tuft of several
fronds, growing from six inches to a foot, sometimes more,
in height. The stipes, which is very brittle, dark-coloured,
and shining, with a few small scales at the base, is usually
rather more than a third of the length of the frond, and
generally erect. The form of the frond is lanceolate ; it is
bipinnate, the pinnæ lanceolate, the pinnules ovate acute,
cut more or less deeply on the margin, the lobes furnished
with a few pointed teeth. In some of the plants, and
usually owing to their vigour, the pinnules are so very
deeply cut as to become pinnatifid, almost pinnate, the lobes
themselves then resembling the smaller pinnules nearer the
apex of the pinnæ and frond.
The venation is very readily seen, owing to the delicate
texture of the frond. In the ordinary-sized pinnules there
is a somewhat tortuous midvein, which gives off a lateral
branch or venule to each of the lobes into which the margin
is cut, these venules branching again into two, three, four,
or more veinlets, according to the size of the lobes, and each
ill
Plate X.
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