62 FERNS : BRITISH AND FOREIGN. 



endowed with very different natures, for tte vitality 

 and tensicity of life is much greater in the Eremoi 

 hryous than in the Desmohryoiis division j and it is not 

 a little remarkable that so far as observations upon 

 cultivated plants enable me to ascertaiuj 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 Hfe in Eremohrya I may men- 

 tion that in importations of Ferns from distant countries 

 those belonging to that division generally arrive in a 

 living state, while Desmohryous 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 



