126 ACCLIMATIZATION. 



species is adapted to the climate of its own home : species 

 from an arctic or even from a temperate region cannot 

 endure a 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 most cases very close, we have 

 evidence with some few plants, of their becoming, to a cer- 

 tain extent, naturally habituated to different temperatures ; 

 that is, they become acclimatized ; thus the pines and rhodo- 

 dendrons, raised from seed collected by Dr. Hooker from 

 the same species growing at different heights on the Hima- 

 layas, were found to possess in this country different 

 constitutional powers of resisting cold. Mr. Thwaites in- 

 forms 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 ani- 

 mals, several authentic instances could be adduced of 

 species having largely extended, within historical times, 

 their range from warmer to colder latitudes, and conversely ; 

 but we do not positively know that these animals were 

 strictly adapted to their native climate, though in all ordi- 

 nary cases we assume such to be the case ; nor do we know 

 that they have subsequent!}'' become specially acclimated to 

 their new homes, so as to be better fitted for them than they 

 were at first. 



As we may infer that our domestic animals were origin- 

 ally chosen by uncivilized man because they were useful, 

 and because they bred readily under confinement, and not be- 

 cause they were subsequently found capable of far-extended 

 transportation, the common and extraordinary capacity in 

 our domestic animals of not only withstanding the most 

 different climates, but of being perfectly fertile (a far severer 

 test) under them, may be used as an argument that a large 

 proportion of other animals now in a state of nature could 

 easily be brought to bear widely different climates. We 



