288 BORDER SPECIES. 
the polypody, osmunda, adder’s-tongue and climbing fern 
families. 
Our species is one of the most widely distributed of its 
tribe. It is found in the Tropics of both Hemispheres 
and in many parts of the Temperate Zones. In America 
it grows from Kentucky to Florida, inhabiting wet rocks. 
The rootstock is slender, cordlike, covered with dark 
hairlike scales and often creeps extensively. In the 
warmer parts of the earth it ascends trees to heights of 
several feet. There is considerable variation in the 
fronds from different regions. In specimens from Ken- 
tucky and Alabama the blades are long and narrow and 
an inch or more wide at base, tapering upward to the 
slender apex. They are pinnate, with ovate, deeply cut, 
blunt pinne or are often twice pinnate in the lower part. 
The lobes of the pinnules are fre- 
quently toothed, especially at the 
ends, and the rachis is green and nar- 
rowly winged. 
The sori are borne on the lobes of 
the pinnules, usually on the outer 
basal lobe. The sporangia are clus- 
tered around a slender bristle which 
A FRUITING PINNULE. is a prolongation of a vein and are 
surrounded by a vase-like, slightly two-lipped involucre. 
In old fronds the bristles become long exserted and quite 
conspicuous and have obtained for the plant the name 
of bristle fern. It is called Killarney fern from the fact 
that it is found about the Lakes of Killarney. 
All the species belonging to the Hymenophyllacee 
have very thin and delicate fronds and are commonly 
called filmy ferns. Frequently the blades consist of a 
single layer of cells. Although so delicate, the fronds 
