332 THE SURVIVAL OF THE UNLIKE. [xiX. 



there was a difference of about twenty -three days in 

 favor of the individual of the colder locality, in that of 

 the carpinus about eighteen days, and in that of the 

 tulip tree a similar result was obtained when the com- 

 parison was restricted to buds of the same size and 

 development. The catalpa of the northern locality 

 developed twenty days in advance of the other."* In 

 the instances of the tulip tree and catalpa, "of which 

 very few generations can have been raised in Europe," 

 we have clear acclimatization. 



Winter and spring wheats afford a striking example 

 of acclimatization. In endeavoring to prove the com- 

 mon origin of these wheats, Monnier has given us a 

 case of distinct adaptation to climate : "He sowed 

 winter wheat in spring, and out of one hundred plants 

 four alone produced ripe seeds ; these were sown and 

 re -sown, and in three years plants were reared which 

 ripened all their seed. Conversely, nearly all the 

 plants raised from summer wheat, which was sown in 

 autumn, perished from frost ; but a few were saved and 

 produced seed, and in three jears this summer variety 

 was converted into a winter variety."! 



Plants undoubtedly adapt themselves to dry cli- 

 mates by modifications in form and structure of vari- 

 ous organs. Deep-rooted trees endure drought best. 

 Professor Budd writes to the Iowa State Register that 

 "it is also interesting to note that the deep-rooted 

 sorts [of apples] that endure drought perfectly are 

 native to sections of the earth where this habit of 

 growth is a necessity. As instances : Gros Pommier 

 is native to the sandy, gravelly knolls of east 



•Asa Gray, in American Journal of Science, .'Id ser. x. I'M. Cited also In 

 Essay XVII. 



t Darwin, I.e. i. 380. 



