374 George E. Nichols, 



The association-types of oxbow ponds. — Oxbow ponds have 

 been observed in a few places, as at Margaree Harbor and 

 Pleasant Bay. Such ponds usually support a luxuriant aquatic 

 vegetation, notably such species as the following: 



Sparganium angiistifoliuin Ranunculus aquatilis capillaceus 



Potamogeton hupleuroides Callitriche palustris 



Potamogeton epihydrus Ludvigia palustris 



Scirpus suhterminalis Myriophylliim verticillatum 



Nymphaea advena Utricularia intermedia 



NympJiaea microphylla Utrictdaria vulgaris 

 Castalia odorata 



The marginal vegetation here requires no particular comment. 

 It may include any of the wet marsh species of the flood plain 

 series, in addition to various of the herbaceous plants and shrubs 

 elsewhere listed as characteristic of well-drained swamps. 



4. The Formation-types along the Seacoast 



a. INTRODUCTORY 



In this group may be included all association-complexes of 

 hydrarch origin whose ecological aspect is influenced directly by 

 the proximity of the sea. This influence is seen most obviously 

 in the eflfect of salt water on the character of the vegetation. 

 But beside this, from the standpoint of physiographic ecology, 

 the dynamic agencies which are associated with the activity of 

 waves and currents are of prime importance, either directly or 

 indirectly: the formation and destruction of barrier beaches, 

 which may result in the development of coastal ponds of all 

 degrees of salinity — from completely salt to completely fresh; 

 the deposition of sediment, which under favorable conditions 

 may lead to the development of coastal swamps, etc. With 

 reference to these physiographic agencies, just as was pointed 

 out in discussing the vegetation of uplands along the seacoast, 

 it is possible to divide the associations of lakes and swamps here 

 into two groups : associations along eroding shores, and associa- 

 tions along depositing shores. Little attention has been given, 

 however, to the associations of the first group, which comprise 

 primarily the formation (or formation-complex) of seaweeds 



