1909.] NATURAL SCIENCES OF PHILADELPHIA. 389 



(sp. gr. 1.0000), while Pluchea camphorata mixes its growth with the 

 sedge, as does J uncus Gerardi (J), which surrounds a low sand dune 

 covered with Panicum virgatum. In three isolated areas is found an 

 association of Spartina patens (V), while back of Spartina stricta 

 maritima (X) on the roadside of the lagoon occurs an association of 

 J uncus Gerardi (J), at one end of which Limonium carolinianum enters 

 the association. At the head of the lagoon, at the inner edge of the 

 marsh soil, Cyperus erythrorhizos and Polygonum ramosissimum, which 

 indicate beginning fresh water conditions, have established themselves. 

 Outside of the influence of the salt water, where the inner edge of the 

 salt marsh (sp. gr. 1.0000) owes its wetness to rains and fresh water 

 springs, just in front of the river bluff occur plants of fresh water 

 swamps, such as the shrubs Alnus serrulata, Pyrus arbutifolia, Clethra 

 alnifolia and the herbs Vernonia noveboracensis , Eupatorium pur- 

 pureum, Polygonum sagittaturn, Osmunda cinnamomea, Sagittaria 

 variabilis, Cicuta maculata and Lobelia cardinalis. 



Transition to Fresh Water Ponds. 



Upper Wreck Pond. — We have seen that the appearance of Spartina 

 patens indicates that the soil is only periodically flooded with salt 

 water. Above the carriage road, where the forest approaches the 

 water's edge, Spartina stricta maritima gradually thins out, and its 

 place as a border plant is taken by Scirpus pungens (sp. gr. 1.000), 

 Scirpus lacustris and Spartina polystaehya . But the persistence of this 

 grass here, where the fresh water conditions are becoming pronounced, 

 is perhaps explainable by the fact that the periodic entrance of salt 

 water prevents the replacement of this grass entirely by typic fresh 

 water vegetation, which is unable to survive a short exposure to salt 

 water; while Spartina stricta maritima not only withstands salt water, 

 but actually thrives in it, and also adapts itself to growth in water 

 which varies its salinity within wide limits, becoming almost fresh 

 when the inland rains are especially heavy or when the inlets of the 

 streams are closed by sand bars during severe storms, as during the 

 summer of 1909. During this summer the outlet of Wreck Pond was 

 closed to the sea until, as indicated by the hydrometer, the water 

 became entirely fresh, and yet Spartina stricta maritima and Spartina 

 patens persisted in their usual habitats, flowering as usual, even when 

 partially submerged by the overflow of fresh Avater during heavy 

 summer rains. 9 However, before we reach the place where this change 



9 This matter, as indicated by the sp. gr. hydrometer, will appear in a later 

 paper, but it should be emphasized here that salt water plants stand submer- 

 gence in fresh water much better than fresh water plants in salt water. 



