Accliinatization. 93 



no effect or that partial adaptations appear, of the kind 

 with which we are acquainted through Bonnier's ex- 

 periments with alpine plants.-^ It may also happen that 

 the species in its old locality consists of a group of sub- 

 species of which some are suited to the new climate while 

 some are not; in such a case all that remains to be done 

 is to find out which are suited and which not. 



On the theoretical side we may apply the theory of 

 acclimatization to the solution of the problem of the 

 distribution of a single species over vast regions, as for 

 example in the case of maize in America. The climate 

 of a locality determines the subspecies which inhabit it, 

 sometimes favoring a tall luxuriant plant laden with 

 large ears heavy with seed, som.etimes small plants ripen- 

 ing in a few weeks wnth little ears and seeds (Fig. 20). 



But whether such subspecies have arisen by gradual 

 selection or by mutations can of course no longer be de- 

 termined empirically. 



The process, however, which is really interesting to 

 us here, is the conscious or unconscious selection of in- 

 dividuals which are best adapted to the new conditions : 

 in other words the establishment of a new race bv means 

 of the material supplied by fluctuating variation. 



Before passing on to consider this case in detail I 

 should like to mention an example which more than any 

 other shows how careful we must be in using practical 

 experience for the solution of scientific problems. It is 

 the case of a result obtained by one of the most distin- 

 guished growers in Germany, J. IMetzger, and of its 

 scientific application by Darwin himself, It is the case — 

 so well known and so often quoted — of the transforma- 

 tion of an American variety of maize into the ordinary 



Compare also § 17, pp. 144-146. 



