44 HISTORY OF BRITISH PERNS. 



2. Allosorus = Dorsal -fruited Perns, with, the sori 



covered by reflexed, unaltered margins of the frond. 



B. ASPIDIEJS= Perns whose sori have a special indusium, 



of a circular or roundish form, and springing here 

 and there, from the back of the veins. It contains 

 the genera Wood&a, Lastrea, Polystichum, and 

 Cystopteris. 



3. Woodsia = Dorsal-fruited Perns, having the in- 



dusium attached beneath the sori, and divided 

 into hair-like segments. 



4. Lastrea = Dorsal-fruited Perns, having a reniform 



indusium, attached by its indented side. 



5. PolysticJium = Dorsal-fruited Perns, having a cir- 



cular indusium, attached by its centre. 



6. (^fo^fem==Dorsal-fruited Perns, having a cucullate 



or hooded indusium, attached by its broad base. 



C. ASPLENIE^: = Perns whose sori have a special indusium, 



of an oblong or elongated form, and springing from 

 the sides of the veins. It contains the genera 

 AtJiyrium, Asplenium, Ceterach, and Scolopendrium. 



7. AtJiyrium = Dorsal- fruited Perns, having an oblong 



reniform indusium, attached by its concave side, 

 the other side fringed with hair-like segments. 



