44 HARPER 



Middle Georgia. Others are often weeds, growing in various 

 situations in the southeastern states. The rest are mostly 

 species which have strayed in from the neighboring pine-barrens, 

 hammocks, or sand-hills. 



The origin of this rock outcrop flora, particularly the rarer 

 members of it, is a mystery. As rocks of this kind are so few and 

 far apart it is difficult to imagine how some species could have 

 migrated from one rock to another, a hundred miles away, 

 apparently without establishing themselves in intermediate 

 territory. There is no reason for supposing that the total area 

 of these rocks was ever (at least since the coastal plain received 

 its present plant population after the last submergence) greater 

 than it is now. Perhaps the rock-loving plants from farther 

 inland were among the first to take possession of the coastal plain 

 as it emerged from the sea, and have been gradually driven to a 

 last stand on the rocks, to which they were best adapted from 

 previous experience in the Piedmont region. The origin of the 

 three nearly endemic species first mentioned is another problem. 

 The Marshallia and Azalea do not differ very much from some 

 of their relatives, but the Pentstemon is very distinct. 



Further study will doubtless tend to elucidate these problems. 

 In the meanwhile we will pass on to the next habitat-group, 

 namely, 



2. Dry Pine-Barrens. 



The summits and upper slopes of all the ridges (except the 

 sand-hills which will be described later) are covered with dry 

 pine-barrens, which constitute probably at least half the area 

 of the whole Altamaha Grit region. This habitat-group has 

 suffered most from the effects of civilization, for in it are located 

 nearly all the dwellings, farms, and other works of man. Lumber- 

 ing and turpentining have already destroyed the finest pines, and 

 the fires which sweep over this area every winter and spring do 

 great damage to the young trees. But dry pine-barrens are 

 so abundant that suitable portions of them for study can be found 

 on almost any square mile, and it is easy to allow for the effects 

 of civilization and imagine just what the natural condition of 

 this group should be. (For illustrations see Plate II.) 



