1904.] NATURAL SCIEXCE3 OF PHILADELrHIA. 613 



and numerous shrubs, shrubby herbs and herbaceous perennials, 

 together with a few annuals. Four species of palms belonging to the 

 genera Sabal, Serenoa, Coccothrinax, and the Sago palm, Zamia 

 floridana, are prominent representatives of the pine-land formation. 

 These pine-lands are light and any, with comparatively thin soil. 

 The growth of timber is scattered and the plants found in this for- 

 mation are not duplicated in the West Indies. Relatively, then, the 

 flora of the pine-land formation is younger than that of the hummocks, 

 and may be older or younger than the everglade formation, according 

 to whether this association of species encroached on elevated plain 

 land or whether it captured grassland or an everglade formation. 

 The evolution of the pine woods may be represented for sake of 

 clearness diagrammatically as follows : 



Very Shallow Water 



Dry Elevated Sea Bottom Swamps 



I 

 Savanna Grassland 



Pine Woods 



The culmination from either condition has been a pine forest. 



The everglades, then, historically speaking, may be older than the 

 pine woods, or they may be younger. WTiatever their position in point 

 of time, they cover an area of about one hundred miles wide and perhaps 

 one hundred and fifty miles long, the elevation being about eighteen 

 feet above sea-level. This area consists of an extended saw-grass 

 swamp traversed by winding river channels, and covered with scattered 

 hmnmock-lands. Its flora consists of grasses, sedges and other herba- 

 ceous plants, among which are many aquatic and mud-inliabiting plants. 

 The vegetation of the everglades is of a more northern character than 

 that of the hummock-lands. 



The mangrove formation represents an important element in the 

 flora of southern Florida. The mangrove swamps are particularly 

 abundant along salt or brackish shores and along the sea islands, the 

 so-called Florida Keys.^ Their vegetation is confined almost exclu- 

 sively to the mangrove trees and such few Tillandsias and orchids as 

 grow upon their branches. Frequently on the borders of these swamps 

 occurs a large showy species of AcrosticJium with leaves often six to 

 eight feet long. The area shut off from the sea by the fringe of man- 



* Phillips, O. P., "How the Mangrove Tree adds New Land to Florida," The 

 Journal of Geography, II, 1-14, January, 1903. 



