614 



PROCEEDINGS OF THE ACADEMY OF 



[Sept., 



groves becomes dry ground and eventually grassland (in Florida 

 " prairie" ). 



The results of this survey as to the southern extremity of Florida 

 may be arranged below: 



Ancient Strand Flora 



Ancient Sea Island Flora 



Northern Element 



Plain Flora 



Swamp Flora 



Savanna Flora -^ 



Grassland 



Present Strand Flora 



\ > 



Pine-land Flora 



Present Hummock Flora 



Lastly are the ruderal plants and weeds that, introduced by the 

 hand of man, have become established in America. The history of 

 the introduction and spread of many of these plants is known to an 

 exactness, whereas many have appeared and become established the 

 history of which is involved in considerable doubt. The time which 

 has elapsed since the advent of these outsiders does not exceed two or 

 three hundred years, and yet in that time many American varieties 

 of common European plants have by mutation or otherwise arisen 

 to demarcate the American from the European forms. 



I have endeavored to present in this paper the fact that the compo- 

 nent elements of the flora of eastern North America have had an his- 

 toric development, and I have attempted to give the methods of 

 determining their relative or comparative age, as well as the philo- 

 sophic reasons underl3ang their distribution. The outcome of these 

 observations may be tabulated and arranged as follows, the top of 

 the table representing the oldest elements of our flora: 



