GENERA OF FERNS AND THEIR CLASSIFICATION. 59 
ferences pointed out by him constant, which they are 
not, the organs themselves are so minute that the 
study of Ferns would be 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 Royal 
Botanic Garden at Kew, where an unrivalled collection 
of F erns 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 
<c 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 Ees- 
mobrya , 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 Eesmobrya are of equal value 
in a general systematic point of view with Exogen and 
