TRANSACTIONS OF WAGNER 



102 



VEGETATION OF SOUTH FLORIDA 



others have been formed by gradual solution and by the falling of roofs of 

 subterranean water courses. Few of the holes are large enough to be 

 termed sinks. The vertically walled banana holes extending down to per- 

 manent water level form natural wells, the shallow hollows are best termed 

 pot-holes. G. C. Matson and F. G. Clapp* of the Florida Survey, estimate 

 that the rate of solution in the limestone section of central Florida is about 

 400 tons per square mile annually. If evenly distributed, this would lower the 

 surface of the limestone about three decimeters in five or six thousand years. 



The soil which fills these rock basins is a sandy loam and rich in organic 

 matter owing to the collection of vegetal material formed partially under 

 standing water. The edge of these sinks may be a rock rim with vertical 

 sides, or it may blend by gradual slope with the rock surface of the surrounding 

 pineland. These depressions have been formed probably in irregular areas 

 of softer oolite which, less resistant to the solvent action of rain water, has 

 been removed by gradual solution. These pot-holes in South Florida with 

 their characteristic vegetation suggest the limestone sinks in Bermuda, which 

 are filled with a vegetation quite distinct from the cedar-covered hillsides. 

 The "Cockpit Country" in Jamaica is a region of limestone sinks, but in a 

 mountainous country and on a far grander scale. 



Ecologic Considerations. It is noteworthy that a slight difference of eleva- 

 tion makes an entire difference in the vegetation of South Florida. A difference 

 of twenty to forty centimeters may mean a change in the plants which enter 

 into any particular plant formation. Here under practically the same climatic 

 conditions we find plant formations which owe their character to the con- 

 trolling edaphic, or soil conditions. Here on a scale not found elsewhere 

 in North America, the ecologist can study the influence of varying amounts 

 of soil water on the native vegetation of the country. 



The banana holes (Plate III, Figs, i and 2), as depressions in the flat 

 woods, owe their ecologic character to their size, the character of their soil, 

 richer or poorer in humus and the presence, or absence, of standing water dur- 

 ing the whole, or a part of the year. In wet weather some of these pot-holes 

 are filled with water, but during dry weather, the water disappears by seep- 

 age, or by rapid evaporation. The occupancy of these banana holes by the 

 migration of plants, is purely fortuitous,! but the survival of any one species, 



* Matson, G. C., and Clapp, F. G.: Second Annual Report, Florida State Geological Survey, 

 1908-09: 34; Cf. Geikie, Archibald: Text Book of Geology (third edit.): 344. 

 f See what follows under heading " Means of Distribution." 



