HISTORY OF BRITISH FERNS. 



investing membrane or cover to the spore-cases,, and its 

 form,, origin., and mode of bursting when present. This, in 

 fact, brings us to the basis of the classification which has 

 prevailed till within comparatively very few years, and even, 

 to some extent, to the present time. 



Another feature has, however, latterly been adopted by 

 many botanists skilled in the knowledge of Perns, as forming 

 the leading characteristic of their family relationship, the 

 groups thus brought together representing the modern classi- 

 fication of Perns. The feature thus adopted, as affording 

 the marks of family recognition, is the veining of the fronds ; 

 and probably, as at present employed, in conjunction with the 

 characters derived from the clusters of spore-cases and their 

 covers, there is but little scope for further improvement. 

 The tendency of the system is, however, towards subdivision 

 of the family groups, and in this direction it is perhaps 

 somewhat liable to err. "We shall introduce a summary of 

 the groups and species adapted to Mr. John Smith's plan of 

 arrangement, in accordance with the venation ; the picture 

 presented by our few native species must riot, however, be 

 taken as a proper representation of this system of classifica- 

 tion. In the more detailed descriptions it will be more con- 

 venient if we follow an alphabetical order. 



