1915.] NATURAL SCIENCES OF PHILADELPHIA. 419 



THE DIVERSITY OF ECOLOGIC CONDITIONS AND ITS INFLITENCE ON THE 



RICHNESS OF FLORAS. 



BY JOHN W. HARSHBERGER, PH.D. 



The ecologic conditions of vegetation are those which are con- 

 nected with the influence of the environment on the plants. The 

 factors which influence the growth and the cUstribution of species 

 may be divided into Climatic, Edaphic, Physiographic, Biotic, and 

 Chronologic (Geologic-Historic). The climatic factors include the 

 influence of temperature, moisture, light and wind. The edaphic 

 factors are connected with the conditions of the soil. The physio- 

 graphic factors are concerned with the physical structure of the 

 geosphere (land surface) and the hydrosphere (water surface) of 

 our planet. The biotic factors are those in which plants and animals 

 (including man) are influential. The chronologic factors deal with 

 the past geologic and paleontologic conditions of the earth, while the 

 historic data are concerned chiefly with the past distribution of 

 plants and their probable successional history. The diversity of 

 ecologic conditions is the diverse character of the climate, soil, 

 physiography, life and chronology of any region. 



The richness of a flora may be considered from a number of different 

 points of view. We may consider it numerically, that is the actual 

 number of species ; or we may consider its richness in generic types, in 

 endemic types, in introduced plants, in common plants, in rare plants, 

 in relict species, in biologic forms (such as xerophytes, hydrophytes) 

 and in growth forms (trees, shrubs, lianes) or in the types suggested 

 first by Raunkiaer, namely, the phanerophytes, the chamsephytes, the 

 hemicryptophytes, the helophytes and the geophytes. If we use the 

 system of Raunkiaer and arrange the above types by percentages, 

 then we would have a climatic spectrum which would enable us to 

 make a comparison with the floras of other lands and climes simi- 

 larly arranged. An attempt will be made to study the diversity of 

 ecologic conditions and its influence on the richness of the floras of 

 a number of different phytogeographic regions of North America. 

 Those regions will be chosen with which the writer is more or less 

 familiar, and regions which have been studied carefully by other 

 botanists and their floras catalogued. 



