REAL FACTORS IN ACCLIMATIZATION. 39 



at an altitude of 12,000 feet on Long's Peak, in the form of a 

 dwarf shrub scarcely a foot high. That trees show great dif- 

 ferences in their adjustability is too well-known for comment, 

 but it has not been so clearly recognized that the restricted range 

 of a native species may be due as much to a lack of migration 

 as to the difficulty of adjustment to physical factors. The 

 plumed pine (Piiius aristata) is in general restricted to the 

 region of the upper timber line, and the piiion (P. cdiilis) to the 

 lower. This distribution is primarily a matter of migration, 

 shown by the fact that the plumed pine is represented by many 

 outposts due to migration taking place more readily down the 

 mountainside than upward. 



The whole question of acclimatization hinges upon the 

 meaning given to the term climate. In ordinary usage, climate 

 means weather, and it is applied to conditions and areas of the 

 vaguest limits both physically and geographically. General 

 meteorological results which are chiefly restricted to "tempera- 

 ture and rainfall are taken as the usual criteria, and factors of 

 greater importance, water content, humidity and evaporation, 

 largely ignored. The first step toward the exact study of ac- 

 climatization must rest upon a thorough investigation of the 

 many factors that compose a climate. This can only be done by 

 an extensive and intensive study by means of instruments. 



By climate we usually understand the atmospheric factors 

 of a region merely, and, as indicated above, soil factors are 

 equally important, and often more important. For these rea- 

 sons, the ecologist prefers to substitute the term habitat, as the 

 sum of all factors that aflfect the plant, for climate, and to re- 

 place acclimatization by the word ecesis, the process of becoming 

 established in a new home. These terms at least serve the 

 purpose of emphasizing the fact that all of a plant's environment 

 must be taken into account in studying its behavior and struc- 

 ture. Climate is too general as well as too restricted a con- 

 cept for scientific purposes, at least for the biologist. Botanist 

 and horticulturist alike speak of the climate of Colorado, of 

 Nebraska, etc., when as a matter of fact the differences be- 

 tween sets of physical factors, or habitats, within each are often 

 much greater than differences between neighboring States. 



