200 THE ORIGIN OF SPECIES 



region cannot endure n tropical climate, or conversely. 

 So again, many succulent plants cannot endure a damp 

 climate. But the degree of adaptation of species to the 

 climates under which they live is often overrated. We 

 may infer this from our frequent inability to predict 

 whether or not an imported plant will endure our 

 climate, and from the number of plants and animals 

 brought from different countries which are here perfectly 

 healthy. We have reason to believe that species in a 

 state of nature are closely limited in their ranges by 

 the competition of other organic beings quite as much 

 as, or more than, by adaptation to particular climates. 

 But whether or not this adaptation is in mosi; cases very 

 close, we have evidence with some few plants of their 

 becoming, to a certrin extent, naturally habituated to dif- 

 ferent temperatures; that is, they become acclimatized; 

 thus the pines and rhododendrons, raised from seed col- 

 lected by Dr. Hooker from the same species growing at 

 different heights on the Himalaya, were found to possess 

 in this country different constitutional powers of resisting 

 cold. Mr. Thwaites informs me that he has observed 

 similar facts in Ceylon; analogous observations have been 

 made by Mr. H. C. Watson on European species of 

 plants brought from the Azores to England; and I could 

 give other cases. In regard to animals, several authentic 

 instances could be adduced of species having largely ex- 

 tended, within historical times, their range from warmer 

 to cooler latitudes, and conversely; but we do not posi- 

 tively know that these animals were strictly adapted to 

 their native climate, though in all ordinary cases we 

 assume such to be the case; nor do we know that they 

 have subsequently become specially acclimatized to their 



