RARE LOCAL FERNS. 37 



sent out new fronds from time to time, until 1905. In the 

 summer of that j^ear it began to show signs of declining. At 

 present its fate hangs in the balance. Notwithstanding the 

 thousands and tens of thousands of spores shed upon the air by 

 this plant, the most determined search failed to show another 

 specimen anywhere in the region. This occurrence, therefore, 

 is as it were a sporadic case, a fortuitous and evanescent case, 

 of Asplcnium pinnatifidum in Delaware County. But when 

 it comes to a species as rare as this, a case is a case, and to 

 be noted. 



The gentlemen of the Philadelphia Botanical Club have 

 collected remarkably large and handsome specimens of this 

 species on the Susquehanna near York Furnace, and it is 

 understood that the extraordinary thrift of these plants is due 

 in all probability to the fact that they have, by some happy 

 chance, been permitted by their competitors to grow in a spot 

 less lean and exposed than usual. They have managed, 

 somehow, to preempt a little patch of rock where there is some 

 moisture, some shade, some depth of dark, rich earth. And 

 this is one of the reasons for saying that small cracks on blis- 

 tering rocks are, probably, for this species, locations not of 

 choice but of stern necessity. 



One of the most beautiful local ferns is the. cliff brake, 

 Ptihra at)vpnrpurca. In the Philadelphia region this species 

 is confined strictly to the limestone. It occurs in some scar- 

 city on the limestone ledge along Gulf creek, in great quan- 

 tity on the cliffs near Norristown, and thence south-westwardly 

 along the Chester Valley. It is known to grow from Canada 

 west to British Columbia and southward, mostly on limestone, 

 into Mexico. Another species, somewhat smaller, the Pclhra 

 Stellcri, has somewhat the same range, and should be found, 

 though it has not been, in this same vicinity. 



The wall-rue spleenwort { Asplcniiiui ruta-inuraria) has 

 been referred to. It is another limestone species. Dr. Dar- 

 lington, in his "Flora Cestrica," edition of 1837, gives: — 

 " Hab. Limestone rocks : near Brooke's Mill ; not common." 



