ACCLIMATISATION 153 



limited in their ranges by the competition of other organic 

 beings quite as much as, or more than, by adaptation to par- 

 ticular cHmates. But whether or not this adaptation is in 

 most cases very close, we have evidence with some few 

 plants, of their becoming, to a certain extent, naturally 

 habituated to different temperatures; that is, they become 

 acclimatised: thus the pines and rhododendrons, raised from 

 seed collected by Dr. Hooker from the same species grow- 

 ing at dififerent heights on the Himalaya, were found to pos- 

 sess in this country different constitutional powers of re- 

 sisting 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 extended, within 

 historical times, their range from warmer to cooler lati- 

 tudes, and conversely ; but we do not positively 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 

 acclimatised 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 originally 

 chosen by uncivilised man because they were useful and be- 

 cause they bred readily under confinement, and not because 

 they were subsequently found capable of far-extended trans- 

 portation, 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 pro- 

 portion of other animals now in a state of nature could 

 easily be brought to bear widely different climates. We 

 must not, however, push the foregoing argument too far, 

 on account of the probable origin of some of our domestic 

 animals from several wild stocks; the blood, for instance, 

 of a tropical and arctic wolf may perhaps be mingled in our 

 domestic breeds. The rat and mouse cannot be considered as 

 domestic animals, but they have been transported by man to 

 many parts of the world, and now have a far wider range 



