THE CLASSIFICATION OF FERNS. 
47 
the most important additional characteristic called into 
requisition being that derived from the presence or absence 
of a general 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, up to the present time. 
Another feature has, however, latterly been adopted by 
many botanists skilled in the knowledge of Ferns, as form- 
ing the leading characteristic of their family relationship, 
the groups thus brought together representing the modern 
classification of Ferns. The feature thus adopted, as 
affording the marks of family recognition, is the veining 
of the fronds. This character, as employed at the present 
day, in conjunction with the characters derived from the 
clusters of spore-cases and their covers, leaves but little 
scope for further improvement. The tendency of the sys- 
tem is, however, towards subdivision of the family groups, 
and in this direction it is perhaps somewhat liable to err. 
