88S jDLKXAL OI' T^OKKSTin 



climate because the north aspect or higher elevation influences vegeta- 

 tion through increased moisture, diminished temperature, or dififerences 

 in wind exposure. Undoubtedly climate includes the dominant set of 

 factors, and where climate changes radically' in short distances, as it 

 does in the mountainous regions of the West, climatic influences is 

 more noticeable. Where the climate is fairly uniform over large areas, 

 as in a large part of the East, the differences in vegetation are largely 

 due to soil. This condition has been too often ignored, with conse- 

 quent mistakes and confusion. 



Fernald presents convincing evidence of the importance of the chem- 

 ical composition of the soil. With precise detail he gives the occur- 

 rence of jack pine (Piniis banksiana) and of white cedar (Thuja occi- 

 dcntolis) and the character of the geological formation on which each 

 is found. Jack pine is confined to formations without lime ; white 

 cedar, on the other hand, grows best on limestone. On soils deficient 

 in lime it grows poorly or not at all. He states (page 63) that "TJiuja 

 occidcntahs is almost as pronouncedly calcicolons as Piuits banksiana 

 is calciphobious." 



Fernald lays great stress on the importance of recognizing the dis- 

 tinction between plants which grow on lime soils and those which grow 

 on soils without lime. He quotes Praeger's Irish Topographical Hot- 

 any, saying: "The presence and absence of lime is the most impor- 

 tant particular in which petrology affects the distribution of plants. 

 "Why," asks Fernald, "is this almost axiomatic law blindly ignored or 

 only grudgingly admitted by so many American physiographic ecolo- 

 gists and phytogeographers ?" The answer is not far to seek. The 

 ignoring of this axiom is based on a fixed idea, and nothing is more 

 difficult than to change men's views toward an idea which has taken 

 root. A new discovery they will readily accept, but an old theory based 

 on half truths they cling to tenaciously. 



There is such a theory which holds that soil is of little or no impor- 

 tance except in so far as its physical properties, coarseness or fineness, 

 are concerned. For this we have to thank, it seems, the Milton Whit- 

 ney school in the Bureau of Soils. Physical properties are important, 

 but the fertility of the soil in many cases varies greatly without corre- 

 sponding variation in the physical properties.^ Not until the soil is 

 studied from the chemical and biological as well as the physical point 

 of view will the relations between natural factors and vegetation — 

 plant ecology — begin to be adequately understood. 



^ Jolm S. Burd : "Chemical criteria, crop production, and physical classification 

 in tvva soils." »Soil Science. Vol. 5, No. 5. pp. 405-419. May, iQiS. 



