Palmer — Flora of the Grand Falls Chert Barrens. 107 



elsewhere, moisture, drainage, shade and other factors 

 are most important. After the region was elevated above 

 sea level, in the remote past, ages must have elapsed be- 

 fore any great amount of soil could have been formed 

 over most of the area. The greater part of the surface 

 must then have possessed the characters of a rocky bar- 

 ren, with plants gradually appearing that were adapted 

 to such a region. As the process of soil making pro- 

 ceeded the flora would of course undergo a corresponding 

 transition, through the extinction of the old forms, their 

 modification and the introduction of other species 

 adapted to the changed conditions. Possibly in the small 

 isolated rocky barrens of the present time we find sur- 

 vivors of some of the later stages of these ancient floras. 

 In the appended list the species regarded as local or 

 peculiar to the barrens are marked with an asterisk. 



POLYPODIACEAE. 



Cheilanthes lanosa (Michx.) Watt.* Common on cliffs, in fissures 

 and along ledges in barrens. 



Asplenium parvulum Mart. & Gal. Uncommon on faces of cliffs. 



Asplenium platyneuron (L.) Oakes. Common along ledges in bar- 

 lens. 



Asplenium Tricfiomanes L.* Common in clefts and on somewhat 

 protected cliff faces. 



Camptosorus rhizophyllus (L.) Link. Uncommon on moist shaded 

 cliffs. 



Dryopteris marginalis (L.) A. Gray.* Rare at two or three places 

 on shaded cliffs. 



Woodsia obtusa (Spreng. ) Torr. Very common along ledges and 

 in clefts in barrens. 



Equisetaceae. 



Equisetum arvense L. Uncommon in moist places. 



Selaginellaceae. 



Sclaginclla rupestris (L.) Spreng.* Very common in exposed parts. 



Gramineae. 



Digitaria filiformis (L.) Koehler.* Frequent in thin dry soil. 

 Panicum tennesseense Ashe. Common in thin dry soil. 

 Alopecurus geniculatus L. Frequent in wet depressions. 

 Aristida basiramea Engelm.* Common in dry exposed situations. 

 Eragrostis capillaris (L.) Nees. Similar situations to last. Com- 

 mon. 



