138 



The change in the herbaceous and shrubby flora and ground cover 

 is no less manifest. Corniis Baileyi and S'cropliiilaria leporeUa soon 

 appear ; Cclastnts scajidcns becomes a common hane ; and Zanthoxy- 

 luiii americanum grows high above the river. Following these, dense 

 mats of moss and Peltigera cover the sand and aid in the increase and 

 conservation of soil moisture. With them come such pronounced 

 mesophytes as Parictaria pennsylvanica, Aster ohlongifoUus, Any- 

 chia canadeiisis, and finally JVoodsia obtusa and Anenionc canaden- 

 sis. The last species, tog'ether with the soft maple, is sufficient proof 

 of the extraordinary change that has taken place in the w-ater factor. 

 Bare sand is seldom exposed, but is covered with the dense mats of 

 moss and Peltigera, and shaded by the luxuriant tang-le of herba- 

 ceous plants and shrubs. The few bare spots are still occupied with 

 the typical black oak vegetation of Artemisia caudata, Rudheckia liirta, 

 and other similar species. 



The further fate of this association will be described later in con- 

 nection with the vegetational history of the river dune as a physio- 

 graphic form. 



In ihe Hanover area, the conditions which lead to succession are 

 virtually the same as in the Havana area, but a much smaller area 

 has been affected. Psedera quinquefolia is one of the pioneers, as 

 usual, and is followed by a considerable number of species of meso- 

 phytic character. Among- these are the following. 



Trees : 

 Be tula nigra 

 Uhniis aviericana 

 Celtis occidentalis 



Fra.vin us pennsylvanica, 

 var. lanceolata 



Shrubs : 



Ribes gracile 

 Rubus idacus, 



var. aculeatissimus 

 Rubus occidentalis 



Lianes : 

 Sniila.v ecirrhata 

 Sniilax herbacea 

 Menisperniu ni canadensc 



Herbs : 



Polygonatuiu coinniutatuni 

 Silene stellata 



Primus virginiana 

 Rhus glabra 

 C can thus aniericanus 

 Cornus Baileyi 



Rhus Toxicodendron 

 litis vulpina 



Amphicarpa Pitcheri 

 Zica, aurea 



