TRANSMISSION OF MODIFICATIONS 375 



To determine whether in the acclimatization of a race agen- 

 cies are involved other than selection operating upon individuals, 

 it is necessary either to eliminate the results due to selection or 

 else to discover cases in which it does not occur. While the 

 first is all but impossible of accomplishment with any feeling of 

 assurance, the second is, in the opinion of the writer, entirely 

 feasible, especially in certain lines. 



The importance of the whole question and the difficulty of 

 securing reliable data are sufficient excuse for introducing a 

 somewhat full discussion of certain topics which afford evidence 

 upon the question at hand. 



Extent of acclimatization. The power of the individual to 

 adapt itself to changed conditions is something marvelous, as 

 has been seen under the subject of causes of variation and in the 

 discussion of relative stability. This same elasticity of organi- 

 zation is characteristic of races as a whole. By means of this 

 adaptability many species of both animals and plants have 

 totally changed their habitat, and with this change have under- 

 gone the most sweeping alterations. The whale is developed 

 from a land mammal and is suffering degeneracy as a conse- 

 quence. Swine have been adapted from a diet of roots and 

 flesh to one mainly of grain. Horses and cattle in their wild 

 state subsisted entirely on pasture, but with us their diet is 

 from 25 to 75 per cent grain. Sheep are mountain animals, but 

 they have been adapted to the richest pastures and the lowest 

 plains. The turkey, native to North America, is making his 

 way over all the earth, as chickens have scattered broadcast 

 from their native habitat in southeastern Asia. 



The potato, native to the mountains of Peru, is now grown 

 everywhere in temperate regions, though it never succeeded in 

 acclimating in the tropics except in high altitudes. There are 

 evident limits, or else the possibilities are not yet exhausted. 



Corn (maize) will endure but slight change in locality without 

 suffering seriously, yet after a few years it appears to recover 

 tone and succeed. In this way the culture of this crop has been 

 gradually moving northward in the United States, until now it 

 is fully acclimated in regions in which a quarter of a century ago 

 its culture was impossible. So sensitive is the corn plant to 



