GENERA OF FERNS AND TIIEIR CLASSIFICATION. 65 
ent forms and aspects, effected by tbe agency of man 
and by various natural causes ; the difference from the 
original types being often so great, that if evidence of 
the change were not on record, the botanist of the 
present day would be justified in describing them as 
distinct originally created species. With Ferns we 
possess but little evidence of new forms having come 
into existence, the chief examples being found in sev- 
eral intermediate states in the genus Gymnogramme, 
which of late years have made their appearance in 
gardens, and seem to have as good right to be re- 
garded as species as the original typical forms first 
known. If such changes do actually take place, and 
we are to deduce from them that races of intermediate 
forms originate in the progress of time and through the 
causes above alluded to, then great difficultymust attend 
any attempt to define species of Ferns. This is espe- 
cially applicable in determining species from extensive 
suites of herbarium specimens. The number of species 
will be diminished or increased in accordance with the 
botanist’s idea of specific differences : he will either 
amalgamate a number of allied forms under one specific 
name, or separate more or less of them as distinct 
species. On inspecting living examples of allied forms, 
the latter view seems to claim adoption ; for although 
words often fail to convey the differences between 
individuals, still the eye readily detects them, and 
knowing that each maintains its own peculiar phase or 
habit from year to year, the scientific observer con- 
siders himself justified in naming them distinct species. 
It is a botanical rule to retain the names under which 
species are first described, whether continued in their 
original genus, or in whatever genus they may after- 
