68 
species as Athyrium, A. hyalostegium , so Lastrcea-like in character that 
-I should not have hesitated to accept a former name in either group. 
Aspidium Fauriei Christ is likewise rather an A thyrium, but on the 
border. Athyrium meets all the demands previously laid down of a 
fern to be regarded as primitive. 
The constant restriction of the sorus to one side of its vein is the 
most obvious character distinguishing Asplenium from Athyrium, while 
the equal and long development of both sides of the vein, and the conse- 
quent breaking apart of the halves of the indusium, characterize Dipla- 
zium. The larger part ■ of A. thyrium is nearer to Diplazium, and, as the 
genera are usually construed, there is probably 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 pale* of Diplazium. Diplazium as a natural group is also charac- 
terized'by the exceedingly deep and irregular cells of the nether epidermis 
(figs. 29, 30). Athyrium silvaticum 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 indusium 
must be the diagnostic character, leaving Diplazium , what Athyrium can 
not be made, a clear-cut, definable, and within itself a natural group ; 
but, even so, I have some apparently undescribecl 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 Christensen, long known 
as Allantodia, is a near derivative of Callipteris, confined to this part 
of the world. 
Blechnum is an old group. The distribution of the genus, and of 
some species attests this, as do its general morphological 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 
Euhlechnum and Lomaria 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. Blechnum 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 pale*, and very deep epidermal cells of the 
upper surface of the frond, those of the nether surface being very irregular 
(fig. 31). These 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 that 
