102 Bulletin 1, Biological Society of Washington, 1918. 



cultivated land usually being separated from the river by a 

 belt of forest. 



The general fauna and flora of the Upper Potomac hills 

 undoubtedly is shared by the Piedmont Plateau for an indefi- 

 nite distance in each direction away from the river. Ap- 

 parently the variety of animals and plants really is less, 

 back from the river, although it must be admitted that such 

 areas have been much less thoroughly explored. 



Be that as it may, it is highly evident that the Potomac, 

 like most rivers, forms a highway for animals and plants, 

 along which movements are much more obvious than else- 

 where. The Virginia Bluff, because of its practical con- 

 tinuity with the mountainous region upstream and its cool 

 slopes, harbors a fauna and flora, related in many ways to 

 that of the mountains. Illustrative of this fact is the occur- 

 rence of such plants as white pine, Table Mountain pine, 

 hemlock, sweet birch, and rhododendron; such mammals as 

 the wood rat and Microsorex; and such beetles as Cychrus 

 andrewsii, C. viduus, C. unicolor, Ptomophagus ulkei, Plec- 

 trodera scalator and Boros unicolor. 



The Maryland shore of the Potomac, being in direct phy- 

 sical connection with the large Coastal Plain element of our 

 fauna and flora, and having more warm exposures, is more 

 apt to yield organisms of southern affinities. Thus the 

 sweet gum, Spanish oak, willow oak, and trumpet creeper 

 ascend the river much farther on the Maryland than on the 

 Virginia shore. The same is true of such bugs as Echtri- 

 chodia cruciata, Oncocephalus, Stenopoda, Ploariodes, 

 Banasa euchlora and Cosmopepla camifex. Thus it seems 

 that for northern forms the south side of the river is most 

 favorable, and for southern forms the north side. 



The role of the river as a biologic highway is perhaps most 

 evident from the flora of the islands and floodplains. There 

 is a distinct tendency for Piedmont plants to reach their 

 farthest downstream points on islands, for instance, Quercus 

 muhlenbergii and Arisaema dracontium, on Analostan Id., 

 and Cacalia reniformis and Silene nivea, on Alexanders Id. 

 It should be mentioned here that one of our plants appar- 



