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 pinnae or are often twice pinnate in the lower part. 

 The lobes of the pinnules are fre- 

 1)^ quently toothed, especially at the 



ends, and the rachis is green and nar- 

 rowly winged. 



The sori are borne on the lobes of 

 the P innules 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 Hymenophyllaceae 

 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 



