1910.] NATURAL SCIENCES OF PHILADELPHIA. 545 



differences and geographic notes on the component features will be 

 considered later . 



The upland barrens are mostly covered by a sparse growth of 

 timber of markedly xerophytic type. Quercus stellata is abundant on 

 all barrens, Quercus marylandica on most, while with these on the 

 State-line Barrens Pinus rigida becomes a predominant tree. Asso- 

 ciated with these may occur Sassafras sassafras, Acer rubrum and 

 Prunus serotina (the latter two usually in a stunted condition). The 

 round bushy growth of the thick-leaved oaks, with open park-like 

 spaces between, is the characteristic feature of this woodland. 



It is but a step from this type of woodland to that where the open 

 predominates, then to where on the barest ridges there is but scant 

 covering above the rock for any growth whatever. In such exceed- 

 ingly shallow soil, usually a greenish sand with fine portions of Ser- 

 pentine and talc rock interspersed, there is a scattered growth of 

 thin grasses, Aristida cliehotoma, A. gracilis, and Sporobolus vagince- 

 florus, with the nearly equally delicate Polygonum tenue and Aster 

 parviceps pusillus. It is here, locally, that Talinum teretifolium is 

 found. 



In slightly deeper soil, or on rock-ledges, Arabis lyrata, Asclepias 

 verticillata, J uncus secundus and Panicum philadelphicum become 

 predominant plants. Here Arenaria stricta is noteworthy as a local 

 plant. 



In all these the xerophytic habit is marked, mostly taking the form 

 of reduced, narrow or involute leaves, in Talinum teretifolium of 

 succulency; in Arabis lyrata the entire growth is made in the rela- 

 tively moist spring season. 



Scarcely less xerophytic is the herbaceous growth in the numerous 

 park-like openings mentioned. Grasses and sedges form the bulk 

 of the vegetation. Andropogon scoparius (both brown and purplish 

 forms), Panicum philadelphicum, P. spharocarpon, Aristida cliehotoma, 

 A. gracilis, and Scleria pauciflora are abundant, while constant, but 

 individually less numerous, are Sorghastrum nutans, Paspalum pubes- 

 cens, Syntherisma filiformis, Panicum annulum, P. huachucce silricola, 

 P. scribnerianum, Aristida purpurascens, Sporobolus vaginaflorus, 

 Danthonia spicata, Eragrostis pectinacea, Cyperus filiculmis macilentus, 

 Car ex triceps hirsuta and Car ex glaucodea. 



Other constant herbs of the dry open barrens are Juncus secundus, 

 Sisyrinchium mucronatum, Comandra umbellata, Polygonum tenue, 

 Cerastium oblongifolium, Arabis lyrata, Saxifraga virginiensis , Poten- 

 tilla pumila, Hypericum punctatum, Helianthemum majus, Viola 



