EERNS OP GREAT BRITAIN. 61 



7. Ctstopteuis (Bladder-fern). 



1. C.frdgilis (Brittle Bladder-fern). — Wrowd lanceo- 

 late, twice pinnate ; pinnce lanceolate ; pinnules oblong, 

 rather narrowed below, deeply pinnatifid; aegmenU sharply 

 toothed or serrated. This fern, hke all the other species 

 of the genns, is fragile and deUcate in texture, their 

 membrane-hke natnre readily distinguishing the Blad- 

 der-ferns from most of our native plants. The beautiful 

 little species called Brittle Bladder-fern varies very 

 much in form and ia some of its distinctive features, 

 always, however, retaining its fragile nature. Its 

 fronds, which are from five or six inches to a foot high, 

 grow in tufts. The stalk is erect, slender, glossy, of 

 a purpEsh black colour, with a few scales at its base. 

 The variable fronds may be generally described as 

 lanceolate and twice pinnate, having in most specimens 

 their pinnules pinnatifid. Owing to their thin texture the 

 veining is very apparent. Prom a somewhat winding 

 mid- vein a lateral branch runs into each of the lobes ; 

 this again branches into smaller veins, almost every one 

 of these bearing a cluster of capsules at about the 

 middle of its length. The cluster, which is of roundish 

 form, has a loose white membranaceous indusium, at- 

 tached by its broad base at one side only, beneath the 

 cluster. It soon tears into jagged segments, curling 

 under at the part which is jagged, and finally disappears 

 altogether. The roundish form of the indusium in the 

 genera Lastrea, Polystiehum, and the Bladder-ferns, led 

 earlier botanists to include them aU in the Aspidium, or 

 Shield-fern genus. In Cystdpteris, however, the indu- 



