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. 



Tricbomanes Petersii. 



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-quarters of 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 



Trickomanes Petersii. g C n C T a TrichomaUCS 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 



