GENERA OF PERNS AND THEIR CtASSIITCATION. 59 



ferences pointed out by him constant, wliich. they are 

 not, the organs themselves are so minute that the 

 study of Perns would he impeded rather than facili- 

 tated by the laborious microscopic examination de- 

 manded. The spores also vary at different ages, and 

 are thus apt to mislead. No practical advantage is 

 gained by the introduction of such characters ; and 

 natural groups and alliances can be established without 

 them, by employing such tangible characters as do 

 not require much aid from the microscope for their 

 observation. 



I now come to consider the characters taken from 

 mode of growth. My long connection with the Eoyal 

 Botanic Garden at Kew, where an unrivalled collection 

 of Ferns exists, has given me abundant facilities for 

 the observation of growing plants, and after an atten- 

 tive study and close examination of many years I am 

 induced to attach a higher value for systematic pur- 

 poses to the different modes of growth than my con- 

 temporaries may be disposed to do. My views upon 

 this subject were first published in Seemann's 

 "Botany of the Voyage of H.M.S. Herald" (p. 226), 

 and subsequent observations have but confirmed them. 



Ferns present two very distinct modes of growth, 

 the one of which I term Eremobrya, and the other Bes- 

 w,obrya, and these are comparatively as distinct as the 

 primary divisions of flowering plants ; but I do not, as 

 has been suggested, consider that there is any analogy 

 between the structure of the stems of Eremobrya 

 and EndogenS) and Eesmobrya and Exogens, that 

 their respective modes of development are identical, 

 or that Eremobrya and Desmobrya are of equal value 

 in a general systematic point of view with Exogen and 



