Natural History of District of Columbia — McAtee 57 



DISTRIBUTION OF LIFE IN THE DISTRICT OF 

 COLUMBIA REGION. 



THE PIEDMONT PLATEAU AND COASTAL PLAIN AS 

 FATJNAL AND FLORAL PROVINCES. 



In previous chapters some reference has been made to 

 species characteristic of the Piedmont Plateau and of the 

 Coastal Plain. The common boundary of these physiographic 

 provinces is known as the fall line, and its significance as 

 a line of separation of faunas and floras is well worth fuller 

 consideration. 



No matter where the naturalist may carry on his re- 

 searches, he finds species that are near or at the limit of their 

 range. One species leaves off at a certain place, another 

 presses a little farther on ; the observer finds himself at the 

 northern limit of some forms, and at the eastern or western 

 or southern limit of others. 



The problem of defining boundaries that seem significant 

 because of their nearly or quite coinciding with a sufficient 

 percentage of the totality of range limits usually is a most 

 difficult one. To illustrate the case by local instances, it 

 may be noted that present information indicates among 

 others the following terminations of range as the Potomac 

 River is ascended : 



Marshall Hall — Taxodium distichum, Polypremum pro- 

 cumbens, Pluchea camphorata. 



Hunting Creek — Sabbatia dodecandra, Micranthemum 

 micranthemoides, Utricularia macrorhiza. 



Little River Marshes — Echinochloa walteri, Jussiaea 

 decurrens, Cyperus erythrorrhizos, Cyperus michauxianus, 

 Hyla evittata. 



New Cut Road — Liquidambar styraciflua. 



Chain Bridge Flats — Sagittaria rigida, Zizania aquatica, 

 Scirpus debilis, Quercus prinoides. 



Great Falls — Rhynchospora corniculata, Carex decom- 

 posita, Quercus michauxiana, Rumex verticillatus. Parony- 

 chia dichotoma, Ilex decidua. 



