PHENOMENA OF INHERITANCE 217 



of evolution, but that the case is quite different 

 with "sports" ("Hereditary Genius," prefa- 

 tory chapter). 



More recently the entire biological world 

 has been greatly influenced by the "Mutation 

 Theory" of deVries, which has placed a new 

 emphasis upon the importance of sudden vari- 

 ations in the process of evolution. At first 

 deVries was inclined to emphasize the degree 

 of difference, that is the discontinuity, in these 

 variations, but in later works this distinction 

 is given a minor place as compared with the 

 question whether variations are inherited or 

 not. Inherited variations, whether large or 

 small, are called by deVries "mutations," 

 whereas non-inherited variations are known 

 as "fluctuations." The former are caused by 

 changes in germinal constitution, the latter by 

 alterations in environmental conditions; the 

 former represent changes in heredity, the latter 

 changes in development. 



3. Mutations and Fluctuations. — This clear 

 cut distinction between mutations and fluctu- 

 ations marks one of the most important ad- 

 vances ever made in the study of development 



