1904.] NATURAL SCIENCES OF PHILADELPHIA. 611 



4. A relict flora of a former widespread plateau region, similar to 

 the one mentioned for northeastern Pennsylvania, in which we find a 

 close similarity between the flora of some of the higher mountain sum- 

 mits and the flora of the coastal plain. We have previously mentioned 

 in the physiographic changes which have taken place in this mountain 

 region an explanation of such peculiarities of distribution. The pres- 

 ence of Hudsonia montana Nutt. on the summit of the Table Rock is 

 probably thus explained, for Table Rock represents an undenuded 

 remnant of a former jDeneplain. It is likely, therefore, that Hudsonia 

 montana Nutt. was once more extended in its distribution, but has been 

 isolated by the erosion of the plain on which it formerly grew in abun- 

 dance. The presence of LeiophyUum buxifolium Ell., Xerophyllum 

 asphodeloides Nutt., Amianthium rnusccBtoxicum Gray on the mountain 

 summits and on the coastal plain is also similarly explained. 



5. The distribution of plants in the southern extremity of Florida is 

 an interesting confirmation of the historic development of a flora. 

 Seven plant formations can be recognized, viz.: (1) The sea-strand 

 formation; (2) The mangrove swamp formation; (3) The everglade for- 

 mation; (4) The grassland (" prairie " ) formation; (5) The savanna 

 formation; (6) The pine-land formation; (7) The hummock-land for- 

 mation. Historically the sea-strand formation and the hummock-land 

 formation are the oldest, floristically speaking. The strand flora, con- 

 sisting of such plants as Uniola paniculata, Panicwn amarurti, Ipoincea 

 pes-caprce, Batatas littoralis, Iva imhricata, Cakile maritima, Agave 

 decipiens (ontropic section), has existed as an element of the flora of 

 peninsular Florida since the land was elevated above the sea, and 

 perhaps was derived from an earlier seashore flora which existed along 

 the shore of the mainland or the coasts of the larger and more elevated 

 sea islands. 



Nearly all the tropic species recently added to the flora of the United 

 States were discovered in or about the hummocks, which are essentially 

 duplicated by similar formations in the West Indies. The total area 

 of the hummock-land is relatively insignificant when compared with 

 the pine-lands, yet the flora, as shown in the enumeration below^, is 

 as rich, if not comparatively richer; 



Pine-lands, 43 per cent. 



Hummocks, 42 " 



Everglades, 15 " 



The hummocks consist of isolated groups of hardwood trees, shrubs 

 and vines. These hummock formations with an overlying soil thicker 

 than the pine-lands, due without doubt to the accumulation of vegetal 



