188 THE ANATOMY OF SCIENCE 



comparable mth that given to chemistry by the 

 study of the atoms and the sub-atoms. As the 

 atoms are found to be the same in the stars and 

 on the earth, so the geneticists have discovered 

 the same mechanism of inheritance in all the 

 higher organisms. The chromosomes of plants 

 and animals are so much alike that when seen 

 under the microscope a trained observer would 

 frequently be at a loss to say which was which. 

 Mendel's law has not only given a remarkable 

 incentive to scientific research, but it is begin- 

 ning to exert a wide and powerful influence 

 upon the practical breeding of plants and ani- 

 mals. Yet when we inquire whether this law is 

 true, or, in other words, whether it is precisely 

 applicable to all cases which are assumed to 

 come within its scope, the answer will probably 

 be in the negative. The law states that the traits 

 of any one generation are determined according 

 to purely statistical laws by the traits of the 

 ancestors, and by nothing else. Tower's^ obser- 

 vation, of an apparently new species obtained 

 from the potato beetle by breeding in a refrig- 

 erator, has not yet been successfully duplicated. 

 Yet there seems to be no question that environ- 

 ment plays some part in determining the trend 



s Carnegie Institution Publications, No. 48 (1906). 



