BORDER SPECIES. 289 
of our species last for several years, and commonly do 
not fruit until more than a year old. Instead of produc- 
ing fresh sori yearly, the bristles simply elongate and bear 
new crops of sporangia at their bases. In the northern 
parts of its range the Killarney fern is usually found 
beneath overhanging ledges where there is unfailing 
moisture. Our illustration is from specimens collected 
at Havanna, Alabama, by Prof. Underwood. 
Trichomanes Petersit. 
This, the most diminutive of North American ferns, is 
found only in a small area in northern Alabama where it 
grows on the sides of dripping sandstone cliffs. It is 
so small that a silver quarter of a dollar will cover a 
whole colony. The rootstock is creeping, very small 
and threadlike, and the fronds, on the slenderest of stipes, 
seldom grow to be three-quartersof an inch long. They 
are about obovate with usually entire margins. The sori 
are borne on the apex of the fronds and surrounded by 
a slightly two-lipped involucre. The bristle-like re- 
ceptacle is not exserted as in radicans. Our illustra- 
tion is from specimens collected by Prof. Underwood. 
There are nearly two hun- 
dred species of filmy ferns 
in the world about evenly 
divided between the two 
Trichomanes Petersii. genera Trichomanes and 
Natural size. 
Hymenophyllum. They are 
found mostly in tropical regions in sheltered situations . 
on wet rocks, the trunks of trees and on damp earth. 
Only the first mentioned genus is represented with us 
