GEN3EA OP EEENS AND THE-IE CLASSIFICATION. 65 



ent forms and aspects, efiPected by tte agency of man 

 and by various natural causes ; the difference from tlie 

 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 interinediate 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 

 wiU 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 specitio 

 name, or separate more or less of them as distinct 

 species. On iaspecting living examples of allied forms, 

 the latter view seems to claim adoption ; for although 

 words often faU to convey the differences between 

 individuals, still the eye readily detects them, and 

 knowing that eabh maintains its own peculiar phase or 

 habit from year to year, the scientific observer con- 

 siders himself justified in naming tliem 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- 



