193 



closely resembles the flora of a similar stage in sandstone than a young- 

 limestone topography resembles an old limestone topography. A limestone 

 ravine resembles a sandstone ravine far more than a limestone ravine re- 

 sembles an exposed limestone bluff, or a sandstone ravine resembles an 

 exposed sandstone bluff. "We may make the above statements in another 

 form. Rock as such or even the soil which comes from it, is of less im- 

 portance in determining vegetation than are the aerial conditions, es- 

 pecially exposure. And it is the stage reached by the evolution of the to- 

 pography which determines thft exposure." 



Much might be said on this subject of the chemistry versus the physics 

 of the soil. It is discussed by both Schimper and Warming, and even the 

 latter says that the chemistry of the soil best accounts for the halopliytes. 

 In making observations and recording experiments both sides ot the ques- 

 tion must be kept in mind if our conclusions are to be accurate. 



The soil, or edaphic influence is local, and is in direct contrast to that 

 of climate which is widespread. To the latter are due our pineries of the 

 north and also our own growth of deciduous trees. Beech-maple-hemlock 

 forests, the climax type, toward which, it may be said, eveiything is tend- 

 ing, are climatic. Oak societies, on the other hand, are a predominant but 

 not permanent feature of Winona Lake, and the conifers of the Atlantic 

 coast are edaphic, being due to soil or local atmospheric conditions. The 

 first plant societies of a region are the result of extreme or pronounced local 

 conditions and are edaphic. Less pronounced conditions gradually obt<ain 

 and we have climatic types. And even then the types ai*e not permanent, 

 for we have climatic changes. The earth is perhaps gradually growing 

 colder and a period of glaciation may be approaching. Beech fossils m 

 Sweden show the former existence of beech forests in a region which is 

 now too cold for their growth. 



It is the purpose of the author to indicate some of the changes which 

 are now taking place in the region under discussion and to show how 

 edaphic are giving way to climatic influences as the territory develops from 

 youth to maturity. 



Crustal movements and erosion, with its consequent deposition, must 

 be taken into account. By erosion we have the constant wearing away 

 of hills, which is retarded in no small degree by the vegetation growing 

 upon them and the deposit at a lower level of the material carried away. 

 By this process, which is hastened by the decay of plants, in swamp and 

 lake, xerophytic hills and hydrophytic lowlands both become more meso- 



