FERNS OF GREAT BRITAIN. 15 



* Capsules with a vertical elastic marginal ring, which 

 bursts irregularly. 



Sub-Order I. — PoLTPODiACEiE. 



1. PoLYPoDiUM (Poljrpody). — Capsules seated on the 

 back of the frond in circular clusters, without an indu- 

 sium; veins in the British species, simple or forked. 

 Name, from the Greek polg, many ; and pous, a foot ; 

 either from the shape of the frond, or from its numerous 

 roots. 



2. Gtmnogramma. — Capsules seated on the back of 

 the frond, in linear clusters, without an indusium ; veins 

 in the British species, simple or forked. Name, from 

 the Greek gymnos, naked ; and gramma, a line or letter ; 

 from the fancied resemblance of the forked veins to 

 alphabetical letters. 



3. Allosorus (Rock -brake). — Capsules on the back 

 of the frond, the edges of its lobes rolling under, and 

 forming an indusium. Fronds of two forms -. the barren 

 frond leaf-like; the fertile contracted, and bearing the 

 fructification at its margin. Name, from the Greek 

 alios, various, and soros, a mass. 



4. WooDsiA. — Capsules at the back of the frond, 

 covered by a roundish or kidney-shaped indusium, 

 attached beneath the clusters, and cut at the edges into 

 many thread-like segments. Name in memory of Joseph 

 Woods, Esq. Author of " The Tourist's Flora," &c. 



5. Lastrea. — Clusters at the back of the frond, nearly 

 circular, covered by a kidney-shaped indusium, attached 

 at the notched side; veins distinct after leaving the 



