CLASSIFICATION. 



31 



the four following genera, in whicli the covering is im- 

 perfect, the fructiticatiou is marginal, that is, it is borne 

 along the edges of the fronds. In two of these the cover 

 is formed by the bending back of the margin of the 

 frond. 



The w^hole margin rolled back forms a covering in the 

 Bracken {Pteris). (Fig. 18.) 



Fig. 11, Flg.l^. 



Lobes of the margin folded back forms the covering in 

 the Maidenhair {Adiantitm) . (Fig. 1.) 



In the remaining two genera, having an imperfect or 

 modified covering, one of these has a kind of special in- 

 dusium attached behind, and covering the spore-cases as ]i 

 with a hood, in Bladder Perns {Cij stopfer is). (Fig. 19.) 



jt'ig. ly. Fig. 20. 



The other has a roundish, somewhat cup-shaped recep- 

 tacle, with fringed margins (TVoodsia) . (Fig. 20.) 



Thus far we have given the prominent characters of all 

 the genera of British ferns in which the spore-cases are 

 surrounded by a vertical ring. It has already been ob- 

 served that there remains a small group, consisting only 

 of two genera, in which the ring is oblique, and these are 



