io HOW TO KNOW THE FERNS 



feature of the Bracken is the continuous mar- 

 ginal sorus. There is no proper indusium, but 

 the leaf margin curls over and protects the 

 sporangia to some extent. 



(c) Aspidiece. The sorus is in the form of 

 a little rounded heap. The indusium, which is 

 usually kidney-shaped, is supported by a central 

 stalk, somewhat after the manner of a nastur- 

 tium leaf. The Male Fern (Nephr odium filix-mas) 

 belongs to this sub-family, as well as the Bladder 

 Ferns (Cystopteris) and the Woodsias. 



(d) Aspleniece. Here the sorus is elongated 

 or linear. The indusium arises from a vein to 

 which the sorus is attached. Some very charm- 

 ing Ferns belong to this sub-family. Many 

 botanists include the Lady Fern (Athyrium 

 filix-fcemina) in this section. Certain of the 

 Spleen worts (Asplenium) are common. The 

 Wall Rue (A. ruta-muraria) and *the Black 

 Maidenhair Spleen wort (A. adiantum-nigrum) 

 are well known. 



(e) Polypodies. The sori on the underside 

 of the leaves are without any indusium. They 

 are in rounded clusters, and look like small 

 buttons. Polypodium vulgare is one of our 

 commonest Ferns. Some of the other species 

 of this genus, such as the Oak Fern (P. 

 dryopteris) and the Beech Fern (P. phegopteris) , 

 are abundant in some localities. 



(/) GrammitidecB. The Gold and Silver Ferns. 

 The only British species is the Annual Maiden- 

 hair (Gymnogramma leptophylla). The plant 

 occurs in the Channel Islands. This species is 

 one of the few Ferns which are not perennial. 

 The sori, which follow the veins, have no in- 

 dusium. 



(g) Acrostichece. There are no British repre- 

 sentatives of this sub-family. In this case the 



