1909.] NATURAL SCIENCES OF PHILADELPHIA. 391 



One, therefore, notices the entire absence of such typic salt plants 

 as Spartina stricta maritima, Distichlis spicata, Salicornia herbacea, 

 S. mucronata, Limonium carolinianum and Suceda linearis, while the rem- 

 nant of this true salt marsh vegetation left at the margin of the pond, 

 owing to the occasional entrance of salt water, consists of such plants 

 as Spartina patens and J uncus Gerardi. 



Vegetation in Proximity to the Ocean. 



The low ground margining Sylvan Lake at its seaward end is occu- 

 pied by Scirpus pungens at the water's edge, while back of it occur 

 Spartina patens. Hibiscus moscheutos and J uncus Gerardi, together 

 with Elodes virgin tea and J uncus canadensis. The tall reed grass 

 Phragmitcs communis forms a pure association at this level, as does 

 also Cladium mariscoides mixed with. Solidago sempervirens. The 

 cattail, Typha angustifolia, is found in small cove-like indentations 

 of the shore, while Nymphcea odorata with Panicum crus-galli occur 

 in small sloughs found here and there along the outer shore line. The 

 low sand levels above the marsh are covered with Myrica carolinensis, 

 in association with Panicum virgatum, Baccharis halimifolia, Stro- 

 phostyles helvola, Baptisia tinctoria, Vaccinium atrococcum, Ilex glabra 

 and Prunus maritima, extending back to the edge of the woods behind 

 what was formerly, before grading operations altered the original 

 conditions, the dune complex of my earlier papers. The following 

 plants, Vaccinium atrococcum, Ilex glabra and Baptisia tinctoria, which 

 enter the dune formation, may be considered to be elements which 

 have invaded the formation from an inland pine barren source of 

 supply. 



Vegetation Controlled by Fresh Water. 



Early in my study of the flora of Sylvan Lake my attention was 

 directed to the north shore, because the south shore of the lake had 

 been altered too much by the encroachment of the building line of 

 Avon-by-the-Sea. Only a few patches of the original vegetation was 

 left, and so much altered as not worth a detailed study. Three strips 

 of vegetation can be recognized along the northern shore of the lake, 

 and in the description of them which follows the plants will be men- 

 tioned in the order in which they were collected in walking from the 

 western end to the eastern end. This plan is pursued because it was 

 found impossible to recognize associations of the species, because they 

 were so mixed together, especially in the second strip, as not to be 

 separable into distinct groups. 



