148 
HISTORY OF BRITISH FERNS. 
drawn out at the point, the lower pair always longer than 
the next above them. The pinnules, especially those on 
the larger pinnae, are again pinnate ; the alternate pinnules 
being deeply lobed, and the margins sharply serrate. 
The fronds are of a thick leathery texture, with nume¬ 
rous veins. To each pinnule there is a distinct midvein 
midrib or costa, bearing simple or branched veins, on 
which the sori are produced. All the ultimate divisions 
of the fronds, as well as all the larger lobes, have mid veins 
producing these simple or branched veins, and these bear 
the sori near their junction with the midvein, so that the 
sori are placed near the centre of every pinnule or lobe. 
At first the sori are distinct, and have the elongate narrow 
form common to this genus ; but as they become older, 
they often spread and become confluent, so that almost 
the entire under-surface of the frond is covered with the 
spore-cases. The indusium is narrow, with its free margin 
entire: this soon becomes pushed away by the growing 
sori, and is lost. 
This species is very variable. In dry and exposed places 
it is small, and obtuse in its parts, whilst in sheltered, 
shady places it is much drawn out or elongated. The 
extreme states have been considered as varieties ; that in 
