88 Bulletin 1, Biological Society of Washington, 1918. 



reduced or eliminated. Applying these facts to the situa- 

 tion in Maryland and Delaware, and bearing in mind that 

 70.5 per cent of the characteristic pine barren plants are 

 known to occur, it would seem that the chief reason for the 

 lack of true Pine Barrens is that large tracts of the soils 

 which Pine Barren plants are able to monopolize are 

 wanting. 62 



The fact that some of the very elect ° 3 of the Pine Barren 

 flora occur here and there tucked away in bogs, where they 

 are protected from competition with the ordinary vegetation 

 of the district, shows that our region had its chance for Pine 

 Barrens in that there certainly was a movement of the Pine 

 Barren flora over the area. 



This idea is further supported by the character of the 

 fossil flora of the region which includes such Coastal Plain 

 types as Osmunda, Taxodium, Myrica, Planera and Andro- 

 meda. Even Dendrium, one species of which now is a char- 

 acteristic Pine Barren plant, has been found. (See espe- 

 cially papers by Dr. E. W. Berry, Bulletin Torrey Botanical 

 Club, 33, 1906, pp. 103-182 ; 37, 1910, pp. 19-29, and American 

 Naturalist, 43, 1909, pp. 432-436.) 



Leaving in abeyance the question of absolute origin of the 

 Pine Barren flora, it may be stated that general agreement 

 is to the effect that at one time there was a great body of 

 this flora along much, possibly most of the Atlantic Coast. 

 Then came one or more of the later subsidences to which the 

 Coastal Plain has been subjected. These were exceedingly 

 slow, of course, and there was ample time for plants to shift 

 their stations in response to the ever encroaching coast line. 



M In this connection consider R. M. Harper's conclusions: "The most 

 satisfactory system of geographical classification of the vegetation of 

 temperate Eastern North America is one based on geology," and "The 

 coastal plain, which is defined on strictly geological grounds, is probably . 

 the most distinct natural subdivision of temperate Eastern North America, 

 differing notably from all other subdivisions in soil, topography, and 

 geological history, and to a corresponding extent in its flora." (A Phyto- 

 geographical Sketch of the Altamaha Grit Region of the Coastal Plain of 

 Georgia, Ann. N. Y. Ac. Sci. 17, Part I, 1906, p. 342). Also Witmer 

 Stone's remark: "I heartily agree with Dr. Hollick's contention that 'the 

 mechanical structure of the soil' is the most potent factor in the distri- 

 bution of plants" (Plants of Southern New Jersey, p. 81). 



*Lycopodlum carolinianum, Tofieldia racemosa, Abama amerioana, 

 Poli/gala lutea. Ludwigia hirtella, and others. 



