78 DEVELOPMENT AND HEREDITY. 



summer of a cold climate more rapidly than in 

 the longer summer of a more southerly locality. 

 It has been shown by experiment that if wheat 

 be taken from a southern locality to one much 

 farther north, that the wheat will in a few gener- 

 ations grow and ripen as quickly as. the native 

 wheat ; and further, if the seed of this same wheat 

 be returned again, and raised in the south, it 

 requires several generations to regain its normal 

 rate of growth. In this case of the wheat, the 

 difference observed in the different localities must 

 be primarily due to a difference in the "forcing" 

 qualities of the season, i.e. the more sudden change 

 of temperature and other seasonal conditions gives 

 a stronger and more effective stimulus, and a 

 gradual change gives a weaker stimulus. How- 

 ever, the chief interest lies in the persistence of 

 the effects. We have only to imagine the peculiar 

 conditions of an environment to have acted for 

 an indefinitely greater time, in order to account 

 for the production of permanent methods of growth 

 which produced the so-called "fixed" or hereditary 

 characteristics of species. 



