PHILIPPINE SPECIES OF ATHYRIUM. 
287 
species. If they be classified arbitrarily by the sori, some species appar- 
ently related to other Athyria , but without known equally near relatives in 
Dryopteris, will fall unnaturally in the latter genus. Also I have recently 
ascribed to Dryopteris, as D. dubia 3 a fern the most of whose sori are 
athyrioid ; the reason being that it seemed more closely related to certain 
unmistakable species of Dryopteris than to any Athyrium, and it is ap- 
parently as near to Acrophorus as to either of these genera. 
Milde’s anatomical criteria seem to serve almost perfectly for the 
distinction of Athyrium from Asplenium. The difference in sorus form 
is convenient, but, by itself, an unreliable criterion. As a matter of 
fact, the Diplazia with asplenioid sori always betray their true nature to 
the naked eye by characteristics of form, and of color and texture of the 
fronds, roots, and paleaa. The other derivatives of Athyrium are easily 
distinguished by obvious and familiar characters. 
ATHYRIUM Roth. 
The central and most primitive genus of Asplenieae, typically distin- 
guished from Dryopteris and other primitive Polypodiaceae by having 
an elongate, indusiate sorus, and the critical primitive Athyria having 
usually finely cut and non-deltoid fronds ; distinguished from Asplenium 
by having paleae 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 peripheral 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 Diplaziopsis by the rupturing indusium of the latter 
and its combination of thin lamina and anastomosing veins; and from 
Blechnum 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. 
3 Elmer’s Leaflets, 1 (1907) 235. 
