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 AcUantum-nigrum are triangular, or 

 broadest at the base. The pinnse 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 



