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HISTORY OF BRITISH FERNS. 
The pinnae are jointed to the rachis, and when old are 
readily displaced, so that eventually the black rachis is 
left denuded among the tuft of fronds. A distinct midvein 
passes through each pinna, giving off on each side a series 
of veins bearing venules, the anterior of these producing 
the linear sorus just within the margin of the pinnae. 
The sori, which in the young state are covered by thin 
indusia having a somewhat crenulated free margin, very 
frequently in a later stage become confluent, and cover the 
whole of the under-surface. 
A very rare and very curious variety of this species, 
named incisum, has the pinnae deeply pinnatifid, with 
linear notched segments. Another, equally rare and still 
more beautiful, has the ends of the fronds tasselled ; this 
is called cristatum. There are some forms with the fronds 
two or three times forked, the pinnae depauperated, and in 
one instance deeply lobed. 
The species occurs rather plentifully, growing on rocks, 
old walls, and ruins, and less frequently on hedgerow 
banks. It is pretty generally distributed throughout the 
United Kingdom and Ireland ; and also occurs through¬ 
out Europe, and in each of the other divisions of the 
globe. 
