366 * BOTANICAL GAZETTE [may 



with the St. Mark's River, which emerges from a subterranean 

 course as a series of sinklike ponds, and finally as a surface stream 

 flowing across the sands to the Gulf. At the natural bridge the 

 banks are definite and rise directly from the water level. A rich 

 hammock borders the banks, the trees and shrubs growing close 



to the water's edge. 



Summary 



This local study of the Gulf section of the coastal plain may 

 serve to suggest several points in the successional history of the 

 plant associations of the region. Extremes of xerophytic, hydro- 



meso 



most 



by the long-leaved pine 



oak forest of sterile, sandy soil. The most mesophytic associ 

 is that of the hammocks, occurring on the upland as the c 

 and also as a temporary climax in the river valleys, being com 



and evergreen, of which 



difolia 



most significant deciduous tree, and Magnolia grandiflora L. the 

 principal tree among the broad-leaved evergreens. Between these 

 two extremes are the gradations from pioneer pines through the 

 pine-oak and oak-hickory stages. Telescoping and rapid growth 

 in the later stages are characteristic and confusing. 



The long-leaved pine-saw palmetto association on the flat, 

 poorly drained sands presents a large edaphic problem. With 

 improvement in drainage, aeration of the soil, and consequent pro- 

 motion of soil organisms and their work, the change to a mixed 

 forest can take place, as is seen along the streams as well as in local 

 hammocks which have evidently been built up gradually. Drain- 



palmetto 



into association with the long-leaved pines, and the succession out- 

 lined from dry pine woods to the climax forest will naturally follow. 

 With slight depression of the surface a change to a moorlike swamp 

 results. 



The various types of swamps, characterized by the prevailing 

 species, as the cypress swamps, gum bogs, pine swamps, and bays, 

 and their transitions to the surrounding forest, furnish opportunities 

 for intensive studies. 





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