62 
FERNS : BRITISH AND FOREIGN. 
endowed with very different natures, for the vitality 
and tenacity of life is much greater in the Eremo- 
Imjous than in the Desmobryous division ; and it is not 
a little remarkable that so far as observations upon 
cultivated plants enable me to ascertain, the latter are 
freely reproduced from spores, while the former are in 
proportion rarely reproduced by that means. In confir- 
mation of this tenacity of life in Eremobrya I may men- 
tion that in importations of Ferns from distant countries 
those belonging to that division generally arrive in a 
living state, while Desmobryous ones, particularly those 
with sarmentum, are often killed in the transport. 
I have now briefly reviewed in chronological order 
all the organs or structures upon which pteridologists 
rely for the formation of genera. Unfortunately, 
scarcely two can be found who agree as to the 
principles upon which genera of Ferns should be 
founded, or as to the value of the several organs for 
generic purposes. Some apply to Ferns the princi- 
ples which characterize the genera among flowering 
plants, depending for the most part upon characters 
taken from the organs of reproduction. Others place 
great reliance upon the different modifications of 
venation ; whilst I believe I stand alone in endeavour- 
ing to obtain natural genera, that is, genera having 
species associated by general habit and appearance, 
and by employing auxiliary characters taken from 
the modes in which the plants grow. Habit is not 
excluded from generic characters of flowering plants ; 
indeed numerous instances might be quoted in which 
it is allowed by eminent botanists to constitute the 
chief distinction between allied genera, and by intro- 
ducing it into the characters of Fern genera, more 
