ON GENERA AND SPECIES: ? 
Species will vary according to the evidence possessed by 
different authors, and the views they take of the apparent 
transition forms. 
In verification of what is stated above respecting species, 
I quote the words of an eminent botanist, that “the pre- 
liminary exact determination of what is a species no one 
has yet succeeded in giving.” It is well known that phæ- 
nogamous plants assume different forms and aspects brought 
about by natural causes or the agency of man ; the differ- 
ence 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 species, and originally created as such. With 
Ferns, we possess but little evidence of new forms having 
come into existence in modern times, the chief examples 
being found in several intermediate states in the genera 
|... Gymnogramme and Pteris, which of late years have made 
: their appearance in gardens, some being so different from 
their supposed parents that, if they had been found wild 
~ they would by some botanists be considered sufficiently 
_ distinct to rank as species. If such changes do actually 
E 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, great difficulty must 
-~ attend any attempt to define species of Ferns. 
These observations show the principal conflicting causes 
that have led to the confusion in the nomenclature of Ferns. - 
. This may be considered a sufficient history of species. I 
Will now treat of genera and their classification ; but to 
Parta of EH on which pu are ) founded and SANE Ss SE 
Make the subject well understood, I deem it best to give X = 
first a general exposition of the structure of the different ` 
