70 ON GENERA AND SPECIES. 



I have also to notice that articulation is not confined 

 to the stipes alone ; the segments of fronds laciniee, 

 pinnse, 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- 

 chlcena, 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, Platy cerium, 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 they 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 j 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 

 Linnaeus and Swartz ; while others, as shown in the pre- 

 ceding pages, break up these large genera into a number 

 of smaller ones. 



These different views are consequent on there being no 



