70 ? |. QN GENERA AND SPECIES. 
I have also to notice that articulation is not confined : 
to the stipes alone; the segments of fronds—lacinia, 
pinne, and pinnules—being in many instances articu- 
late with their respective rachis, whether primary or 
secondary. This is particularly characteristic of the 
genera Drynaria, Arthromeris, Schellolepis, and Photino- 
pteris in Eremobrya; and Nephrolepis, Isoloma, Didymo- 
chlena, Cystodium, and others in Desmobrya, as also in 
Scaphobrya. 
: By paying attention to these points they are found: 
serviceable in determining the natural affinity of species. 
Several of the above genera, as also Arthrop teris, Cerato- 
pteris, Platycerium, and Amphiblestra, possess characters 
peculiar to themselves, which necessitates their considera- 
tion as aberrant genera ; consequently the nature of their 
fructification, venation, and habit, must be conjointly 
viewed in determining the tribe to which a seem most ` 
naturally to belong. 
On taking a retrospective view of the preceding obser- 
. vations, it will be seen that every defined form of the - 
organs or structure that serve for defining genera, whether - 
‘artificial or natural, are liable to vary more or less from — 
the adopted typical normal form, and thus afford ample 
scope for Pteridologists to name and classify genera 
according to their views of the value of the several ` 
organs. On this point two authors seldom agree; hence 
great confusion is introduced into the nomenclator of ` 
Ferns. Some may be called conservative, such as Hooker 
and Mettenius, who maintain entire the old genera of 
Se and Swartz; while others, as shown in the pre- 
 eeding pages, break up these large genera into a number 
of smaller ones, 
These different views are consequent on there VE 
