1915.] NATUKAL SCIENCES OF PHILADELPHIA. 425 



comparative figures. Small includes in his Flora of the South- 

 eastern United States (1913), 6364 species and 1494 genera, giving 

 a generic coefficient of 23 per cent. The total number of genera 

 and species in Gray's ManuaP^ is 821 genera and 3413 species, or 

 24 per cent., for the British flora 734 genera and 2964 species, or 

 24 per cent., and for Switzerland 659 genera and 2453 species, or 

 27 per cent. 



If we place in sequence the numbers which we have given above, 

 it becomes evident that we can arrange our regions so that we dis- 

 cover that no two places are alike with respect to the diversity of 



the physiographic conditions. 



Generic 

 Region. Species. Genera. Coefficienr. 



Point Pelee, Ontario 623 466 74.7 per cent 



Florida Keys 533 346 65 



Miami, Florida 796 466 .59 



Hartsville, South Carolina 628 344 54.6 " 



Altamaha Grit Region, Georgia 797 404 50 



Pine Barrens, New Jersey 555 250 45 



Jackson County, Missouri 1141 500 43.8 



Lancaster County, Pennsylvania 1464 617 42.1 "■ 



Yosemite National Park (incomplete) 741 311 41.9 " 



Upper Susquehanna 1105 462 41.8 



Columbia, Missouri 1058 435 41.1 



Tennessee 628 344 34 



Alabama 2.502 822 32.8 



Connecticut 1942 621 31.9 



New York and vicinity 2038 830 31.3 



Pennsylvania 2275 680 29.8 



Switzerland : 24.53 659 27 



State of Washington 2219 614 26.9 



Colorado 2912 702 24.1 



Northeastern United States 3413 821 24 



Great Britain (Druce) 2964 734 24 



Central Rocky Mountains 2733 649 23.7 



Southeastern United States 6364 1494 23 



The figures of this table are a partial confirmation of Jaccard'.s^ 

 law of plant distribution, applied for the first time to a statistic 

 .study of the American flora. It seems, therefore, ''that the generic 

 coefficient is inversely proportional to the diversity of ecologie 

 conditions." Such regions as the central, northeastern and south- 

 eastern United States, central Rocky Mountains, Great Britain, 

 and Switzerland have ecologie conditions of the greatest diversity, 

 and hence low generic coefficients, while the Pelee region, the Miami 

 region and that of the Florida Keys with fairly uniform physiography 

 have relatively high generic coefficients. 



'« Robinson, B. L., and Fernald, M. L.: A Handbook of the Flowering Plants 

 and Ferns of the Central and Northeastern United States and Adjacent Canada, 

 1908. 



