424 PROCEEDINGS OF THE ACADEMY OF [Julv, 



spermaphytes, in a region of great physiographic diversity comprises 

 822 genera and 2502 species, yielding a generic coefficient of 32.8 

 per cent. 



However, if we use Coulter and Nelson's New Manual of Botany 

 of the Central Rocky Mountains (1909), we find that 23.7 per 

 cent, is the generic coefficient for that region where the diversity of 

 land configuration is great and where the ecologic conditions present 

 striking differences. There are listed in this manual 649 genera 

 and 2733 species. 



The differences presented by the generic coefficients of different 

 countries is illustrated by reference to the Flora of the State of 

 Washington, by Charles V. Piper (1906), and by an enumeration 

 of the genera and species given in Jepson's Flora of Western Middle 

 California (1901). The first work gives 614 genera and 2279 species, 

 as the richness of the Washington flora, while Jepson's book includes 

 421 genera and 1449 species. The generic coefficient for the flora 

 of Washington was determined to be 26.9 per cent, and for that of 

 western middle California 29 per cent. 



In such regions as the Appalachian Mountains, which represent 

 an ancient upheaval, and are covered with a deciduous forest, which 

 has occupied the region since the Miocene, the chronologic factor 

 must be considered as one of the factors influencing the numerical 

 richness of the flora. This fact is also illustrated in California, 

 where the diversity of the coast flora in endemic types, as contrasted 

 with that of the Sierra Nevada Mountains, is linked intimately with 

 the past geologic history of the country. Although possessing many 

 species in common, the flora of the coast ranges of California Is 

 decidedly different from that of the Sierra Nevada. Jepson regards 

 the flora of the California coast ranges as a decidedly endemic one, 

 much older and more unique than that of the Sierra Nevada. An 

 examination of a list of plants peculiar to the coast ranges and 

 the Sierra Nevada will show that the coast ranges lack those northern 

 genera which we may call boreal-alpine, while the list of genera 

 found in the Sierra Nevada includes such boreal-alpine genera as 

 Bryanthus, Cassiope, Sibbaldia. This difference at once emphasizes 

 the fact, that to explain the floral diversity and the generic coefficient, 

 we must emphasize not only present conditions of physiography 

 as effective, but we must study the geologic history of the region as 

 \vell, as the past distribution and past successional phases of the 

 land and water plants. 



Before summarizing, it is important to give a few additional 



