I'llILirnXE SPECIES OF ATllYUU'M. ^ 287 
species. If they be classified arbitrarily by tbe sori, some species appar- 
ently related to other Afhyria, but withoiit kjiown equally near relatives iu 
Dryopteris, will fall unnaturally in the latter genus. Also 1 have recently 
ascribed to Dryopteris, as D. duhia,^ a fern the most of whose sori are 
atln-rioid; the reason being that it seemed more closely related to certain 
unmistakable species of Dnjopteris than to any Athyrium, and it is ap- 
parently as near to Acropliorus as to either of these genera. 
I\Iilde's anatomical criteria seem to serve almost perfectly for the 
distinction of Athyrium from AspJenlum. Th^ difference in sorus form 
is convenient-, but^ by itself^, an unreliable criterion. As a matter of 
fact, the DlpJazia with asplenioid sori always betray their true nature to 
the naked e3'e by characteristics of form, and of color and texture of the 
fronds, roots, and paleae. The other derivatives of Athyrium are easily 
distinguished by obvious and familiar characters. 
ATHYRIUM Roth. 
The central and most primitive genus of Asplcnicae, typically distin- 
guished from Dryopteris and other primitive Pohjpodiaccae by having 
an elongate, indusiate sorus, and the critical primitive Athyria having 
usually finely cut and non-deltoid fronds; distinguished from Aspleniam 
by having paleaB with thin lateral walls and pigment in the lumen, by 
having in the base of the stipe two vascular bundles which unite above 
to form a peri})heral horse-shoe-shaped one, and by usually having some 
or all of the sori curved across the vein or occupying both sides of it: 
distinguished from DipJaziopsis by the rupturing indusium of the latter 
and its combination of thin lamina and anastomosing veins; and from 
Bleclinuni by having the sori on veins which run directly or obliquely 
toward the margin. 
There are known to me more than fifty Philippine species, all terres- 
trial; but several of these, apparently undescribed, are not taken up in 
this paper. 
•Elmer's Leaflets, 1 (1907) 235. 
