margin is connected on the outer side with the back of the frond. 

 In habit and general appearance our native species of Woodsia are 

 at first sight very dissimilar to the species of the present genus, 

 but Woodsia Perriniana, a North American species, is so like Cys- 

 topteris fragilis, as to be generally confounded with it by a casual 

 observer, while the indusium is only fringed on the margin, thus 

 leaving its involucral character the sole feature of distinction. 



CYSTOPTERIS FRAGILIS. Brittle Bladder-Fern. TAB. XIX. 

 XX. 



Fronds erect, lanceolate, bipinnate : pinnae lanceolate : pinnules 

 ovato-lanceolate, deeply pinnatifid, the segments ovate or lanceolate, 

 sharply toothed or serrated. 



Cystopteris fragilis, Bernhardi. Hooker and Arnott. Babington. 

 Moore. Newman. Cystea fragilis, Smith, Eng. Fl. Cyathea 

 fragilis, Smith, Fl. Brit. E. B. Polypodium, Linnaeus. 



Abundantly distributed over the mountainous and rocky di- 

 stricts throughout the kingdom, and occasionally on old walls and 

 buildings in the lowland counties. It seems to prefer the moist 

 crevices of limestone rocks in the vicinity of waterfalls, but is by 

 no means exclusive in selecting a site, and though most flourishing 

 and exuberant in its growth under the conditions of shade and 

 moisture, is often met with occupying the most exposed situations. 

 The rhizoma is creeping, but extends slowly, branching and forming 

 new crowns around the old one, often several in number during 

 the same summer and autumn. The fronds rise in tufts from 

 these crowns in April, rapidly attaining maturity, and fading in 

 succession as their place is supplied by others throughout the 

 season, until the development is checked by frost. They vary in 

 height, according to circumstances, from two or three inches to a 

 foot or more, and differ much in form and division, even on the 

 same crown : the general outline is lanceolate, more or less elon- 

 gated ; the pinnse, distinct to the apex, occupy more than half the 

 length of the slender rachis, which is smooth, and nearly destitute 

 of scales ; they are for the most part distant, especially the lower 

 ones, not very regularly arranged, but with a tendency to alternate : 

 the pinnules are similarly arranged, equally distinct, and sharply 

 and deeply serrated, the lower ones being often, in fronds of larger 

 size, deeply pinnatifid, or even pinnate. The venation, easily dis- 

 tinguished owing to the delicate translucency of the leafy texture, 

 varies according to the division and serratures of the pinnules : in 

 most instances each secondary vein bears a sorus, not at its extre- 

 mity, but about half-way from its base ; thus the sori form a line 

 on each side, rather nearer to the midvein than to the margin, but 



