146 
HISTORY OF BRITISH FERNS. 
Adiantum-nigrum^ which, in some of its states, very much 
resembles it ; but the outline of the fronds will, we believe, 
almost always separate them, those of lanceolatum being 
lance-shaped, or tapering from near the middle towards the 
base, while those of Adiantum-nigrum are triangular, or 
broadest at the base. The pinnae spread at nearly right 
angles with the rachis, often, but not always, opposite, and 
have an ovate-lanceolate form ; they are again pinnate, so 
that the frond is bipinnate. The pinnules are of irregular 
form, often obovate, or nearly so, sometimes unequally 
quadrate, but always indented on the margin with deep 
sharp teeth, the larger pinnules being first lobed, and the 
lobes toothed, the smaller ones simply toothed. The vena- 
tion is tolerably distinct ; the pinnules each having a 
tortuous midvein, which produces forked veins, and these 
produce veules, one of which extends towards each serra- 
ture. The sori have no very definite order ; they are at 
first oblong, and covered by an indusium of the same form, 
having a lacerated free margin ; but as they become old, 
the sides become bulged out so as to give them a roundish 
form, and the indusium becomes obliterated. 
The variety microdon is a very rare plant, met with in 
Guernsey, in Cornwall, and in Devon. It has pinnated 
