1915.] NATURAL SCIENCES OF PHILADELPHIA. 421 



Harper^ finds that there are 404 genera and 797 species of plants, 

 giving, therefore, a generic coefficient of 50 per cent. 



Miami Florida, is situated on the oolitic limestone formation of 

 south Florida. •* The flat, featureless country is relieved by short 

 streams which drain the Everglades (of simple topography) into 

 the Atlantic Ocean. The sea beaches are of silicious sand. Small 

 enumerates 466 genera and 796 species in his Flora of Miami, and 

 the calculated generic coefficient is, therefore, 59 per cent. 



The Florida Keys^ are of even simpler configuration than the 

 adjoining mainland. There are no running streams and the lime- 

 stone soil is singularly porous. Besides, the islands are narrow and 

 their shores are rocky, of calcareous sands, or mud-fringed. The 

 entire number of genera is, according to Small, 346 and the number 

 of species is 533, giving the exceptionally high coefficient of 65 per 

 cent. 



Selecting a number of other localities, we find that the vegetation 

 of the upper Susquehanna*^ in New York and Pennsylvania is de- 

 veloped on a soil of glacial origin, in fact the whole region was glaci- 

 ated. Here there is a relatively rich flora of 462 genera and 1105 

 species of seed plants and ferns. The generic coefficient of the upper 

 Susquehanna flora, is, therefore, 41.8 per cent. 



Lancaster County, Pennsylvania, is in a region of rich, agricultural 

 development, which has been dependent on the limestone soils, 

 suitable to the tobacco plant, which thrives upon such soils without 

 depleting seriously the natural mineral fertilizers. The county is 

 in the rolling Piedmont district where the hills are rounded, the 

 streams quiet and the topography comparatively simple and unmoun- 

 tainous with broad, fertile valleys between the ranges of hills. The 

 Susquehanna River runs along the western })oundary for about 

 forty miles and for over one-half of this distance it passes through a 

 canyon with steep sides and a southern exposure where plants of a 

 more southern distribution are at home. Sphagnum swamps among 

 the hills have a more northern flora. Shale and sandstones border 

 the northern part of the county, and south of the middle belt of 

 limestone, schistic rocks occur with some outcrops of serpentine. 



3 Harper, Roland M.: Atm. N. Y. Acad. Set., 17 : 323. 



^ Harshberger, John W.: The Vegetation of South Florida south of 27° .30' 

 North, exclusive of the Florida Kevs, Transactions Wagner Free Institute of 

 Science of Philadelphia, VII, Part 3, October, 1914, p. 183. 



" Small, John K.: Flora of Miami, 1913; Flora of the Florida Keys, 1913. 



* Clute, Willard N.: The Flora of the Upper Susquehanna and its Tributaries^ 

 1898. 



