shrivels and becomes hidden by the bursting of the thecse, or falls 

 off altogether. In some instances, the opening takes place in the 

 centre, the indusium investing the sorus like a cup, when it is 

 styled, though erroneously, an involucre ; while in others, the epi- 

 dermis from both surfaces of the leaf extends beyond the margins, 

 including the thecae between them, and fulfilling the office of indu- 

 sium without being regarded as such : occasionally this marginal 

 separation and extension of the leaf-membrane takes place unin- 

 terruptedly along the whole edge, but it is often only local and 

 about the soriferous extremities of the lateral veins. In a few 

 genera the indusium cannot be traced, the sori appearing to be 

 produced externally : but this, probably in all cases, arises from 

 the very early period of growth at which the disruption takes 

 place, as careful examination of some species of Polypodium readily 

 discovers. 



The application of the term frond to the leaf of a fern is 

 objected to by some botanists ; but the association of organs, that 

 in other plants are simply conservative, with the reproductive 

 function in those before us, is a feature sufficiently remarkable 

 to justify the distinction, and it has thus become almost universally 

 adopted. 



The elegance and variety of the foliage of ferns, rendering them 

 valuable objects in amateur cultivation, with the modes of treatment 

 that experience has proved most successful, will be found in detail, 

 accompanying the descriptions of the several species; but, as a 

 previous provision of material is requisite, and a few general rules 

 applicable in most instances, much repetition may be avoided by 

 a short preliminary notice. No plants are better adapted than are 

 the hardy species of ferns, for filling up shaded nooks in the garden 

 and shrubbery, and for covering the sheltered parts of ruins, 

 grottos, and rock-work, or the margins of ponds and fountains ; 

 shade and moisture being generally favourable to their develop- 

 ment, as is evinced by the natural localities affected by most of the 

 species, which flourish especially under the shelter of woods and 



