` B — — deus sient. 
their ‘fructification, yet a great many differ so widely in. 
general habit and mode of growth, that any systematic 
arrangement, founded on genera so constituted, must be : 
| received as purely artificial, and only admissible on the 
principle of its bringing together under a few brief cha- 
racters a number of species possessing such characters in ` 
common. This being the case, modern Pteridologists have 
found it necessary to seek for other characters in order to 
classify the various groups in accordance with their natural 
relationship to one another, as exhibited by their general 
appearance in habit and mode of growth. This became 
the more necessary on account of the great increase in the 
number of species from time to time brought into notice  . 
by botanical collectors as previously explained. Robert ` i 
Brown was the first to point out and use an additional 
character for defining genera, In 1810, in characterising 
the genera Cyathea, Hemitelia, and Alsophila, he took into 
account the difference of the position of the sori on the | 
p veins, and this he again brought into special notice in the ` 
character of his genera Matonia and Hypoderris, first de- 
scribed in Wallich's “Plante Asiatice. Rariores.” In 
: dium into groups of species naturally allied in general 
2 habit, on characters derived from the structure of the 
s 2 venation and position of the 
f commenced a work entitled « 
