58 Bulletin 1, Biological ^oeieti/ of Wa-'^lriiu/ton, 1918. 



Seneca Creek — Quemis digitata, Querciis i)liellos, Teeoma 

 radicans. 



In the reverse direction there is a similar graduation in 

 the ranges of the iiphmd forms, for instance: 



Great Falls — Asplenium montanum, Khus aromatica, 

 Viburnum pubescens. 



Stubblefield Falls— Betula lenta. 



Little Falls — Raptisia australis, Lathyrus venosus, Cea- 

 nothus ov'atus, Allium cernuum, Eupatorium altissimum, 

 Rudbeckia triloba, Coreopsis tripteris. 



Rosslyn — Bicuculla canadensis, Bicuculla cucullaria, 

 Cornus alternifolia, Solidago canadensis. 



Marshall Hall — Cystopteris fragilis, Athyrium pycno- 

 carpon. 



Occoquan — Pinus strobus, Tsuga canadensis. Rhododen- 

 dron maximum. 



Charles County, Md. — Quercus imbricaria. 



If the whole catalogue of plants were searched for such 

 records, and the whole body of other organisms laid under 

 contribution, there would hardly be a rod of ground along 

 the Potomac that would not be distinguished as the farthest 

 point in the upward or downward extension of some species. 

 No doubt a similar condition exists with reference to species 

 whose chief ranges lie to the east and to the west of this 

 region. 



As previously remarked, this state of affairs makes it 

 diflHcult to point out significant lines between distributional 

 areas. In a country without salient topographical features 

 the odds against success are practically prohibitive. Where 

 natural barriers exist the task is more hopeful. A barrier 

 does exist in the vicinity of Washington, and its importance 

 is such that the distribution of life of this area cannot be 

 properly conceived nor adequately discussed without taking 

 cognizance of it. This barrier and boundary line, or rather 

 zone, is the common border of the Atlantic Coastal Plain 

 and the Piedmont Plateau usually referred to as the Fall 

 Line. 



So far as it conveys the idea of a sharp division between 

 phj'siographic i^rovinces, the term Fall Line is a misnomer. 



