35 



nules ; this is especially the case where the plants are grown in 

 pots in the greenhouse, or in very sheltered situations in the open 

 fernery. 



P. angulare and its yarieties are less hardy than aculeatum, and 

 are not so strictly evergreen, a consequence probably of the greater 

 laxity of their tissue. They seem to require more careful drainage, 

 a lighter soil, and complete shelter from the sun and cold winds. 

 It might be a subject of question, whether these facts may not 

 indicate that very specific distinction which previous remarks tend 

 to set aside ; but in opposition to any suggestion of this kind, it 

 may be remarked, that division, variegation, or laxity of the foliage, 

 constituting variety among the higher orders of plants, is almost 

 universally accompanied by a less robust constitution than that 

 belonging to the normal condition of the species. 



Genus 5. CYSTOPTERIS. 



GEN. CHAR. Sori roundish. Indusium attached by its broad 

 hooded base beneath the sori, with a lengthened, fringed, free 

 margin, opening towards the apex of the segment. 



The British species of this genus are small, elegant ferns, of a 

 very delicate, almost fragile texture; they are well adapted for 

 house culture, throwing out their beautiful fronds, profusely 

 sprinkled with fructification, in all seasons, when sheltered from 

 the frost, the first approach of which, however, destroys them in 

 the open air. They grow naturally on rocks and walls, chiefly in 

 alpine and subalpine districts ; and notwithstanding their delicate 

 appearance, few of the smaller ferns are equally capable of living 

 in a dry atmosphere, or exposed to the action of the sun. 



The indusium is hollow at the base, forming a sort of hood fixed 

 by its inner margin, that is curved beneath the sorus; the remark- 

 able extension of the outer margin is best observed when the thecse 

 have recently burst through their membranaceous cover, which is 

 then seen to be broken unequally into a fringe of narrow, often 

 capillary segments, that becomes eventually reflected. 



The generic name is a Greek compound of /cuo-n?, a bladder, 

 and TTxept?, a ferny in allusion to the peculiar character of the 

 indusium. 



This genus is very nearly allied to Woodsia, differing from it 

 chiefly, if not solely, in the form and attachment of the indusium ; 

 which, in the latter, has its point of attachment beneath the sorus, 

 inclosing it equally all round, and opening in the middle, when it 

 divides into numerous capillary segments forming an involucral 

 fringe around the thecae. In Cystopteris, on the contrary, the 

 attachment of the indusium is rather lateral than basal, and the 



