68 
species as Aihynain, A, UyaJode-yium, so Lastran-\\kG in oharacter that 
I sliould not liavc hesitated to accept a former Tiame in either group. 
Aspidium Fawiei Christ is likewise rather an Atlnjntini, but on the 
border. Atkyrium meets all the demands previously laid down of a 
fern to be regarded as primitive. 
The constant restriction' of the sorns to one side of its vein is the 
most obvious character distinguishing Asplenium from AViyrium, while 
the equal and long development of both sides of the vein, and the conse- 
quent breaking apart of the halves of the indusiuni, characterize Dlplor 
zium. The larger part of AiJiyrium is nearer to Diphzhim, and, as the 
genera are usually construed^ tliere is probabl}' more than one point of 
contact; that is, the line between them is not quite natural and can not 
be made sharp. Most Athyria share the stout habit and rather harsh, 
dark palca; of Diplazium. Diplaziutu as a natural group is also charac- 
terized by the exceedingly deep and irregular cells of the nether epidermis 
(figs. 29, 30). Athyrium sihatiaim shares this character also^ and is 
very much nearer to every species of Diplazium than it is to the primitive 
Athyria.- Yet, if a line is to be drawn between the genera, the indusiuni 
nmst be the diagnostic character, leaving Diplazium, what Athyrium can 
not be made, a clear-cut, defina])le, and within itself a natural group; 
but, even so, I have some apparently undescribed plants not positively 
referable to one or the other. 
Callipteris is an offshoot of Diplazium, still so close that its generic 
separation is a matter of taste. Diplaziopsis, of Christcnson^ long known 
as Allantodia, is a near derivative of CaUipteris, confined to this part 
of the world. 
Bleclinum is an old group. The distribution of the genus, and of 
some species attests this, as do its general morpliological isolation and the 
varied specializations of different species. A very close connection with 
any other forms is no longer to be expected. The merging-point between 
Euhlecltnum and Lomariu must be older than one subgenus and is likely 
to be as old as either, and is therefore most likely to give a clue to the 
affinities of both. Blechnuvi egregium is in this position. It is a stout 
but not very large fern, with stout, erect caudex; rigid, black, partly 
subaerial roots; harsh, black palese, and very deep epidermal cells of the 
upper surface of the frond, those of the nether surface being very irregular 
{fig. 31). Tliese are all notable characters, and their combination in 
this Blechnum, and in Diplazium, and in Athyrium silvaticum^ is 
unmistakable proof of affinity. 
The nearest affinity of Asplenium is to the more primitive part of 
Athyrium. Within itself, it is as diversified in form as might be 
expected of a nonprimitive genus growing in every land in all save 
extreme habitats. But, unlike our other large genera, it is clearly 
definable, and has not given rise to a large" number of other groups 
conveniently distinguished as genera. The reasons for this are tliat 
