276 APPENDIX D 



HUGO DE VRIES considered himself led by his 

 work on the Evening Primroses and by confirm- 

 ing Galton's law of 'recession towards medio- 

 crity ', to the conclusion that evolution proceeds 

 by Mutation or Transilience alone, and that 

 individual differences, called by him 'fluctua- 

 tions', do not lead to marked or permanent 

 change. He does not hesitate to conclude that 

 'fluctuations' are both hereditary and acquired, 

 and that evolution proceeds by the intermittent 

 explosive discharge of an internal transforming 

 force. According to de Vries, the role of Natural 

 Selection is to determine the survival of the fittest 

 among the Mutations scattered in all directions 

 by species during their explosive periods. 



GKEGOR MENDEL. The thoughts of this wonder- 

 ful man should follow those of Darwin, but his 

 great discoveries were so long lost to the world, 

 that their final recognition has produced the most 

 recent of all the phases of evolutionary thought. 

 We are led by Mendel's researches, which it is 

 unnecessary to describe, to the conception of ' unit 

 characters ' : 



'By a unit character in the sense of Mendel's law, we 

 mean any quality or part of an organism, or assemblage of 

 qualities or parts, which can be shown to be transmitted in 

 heredity as a whole and independently of other qualities 

 or parts.' * 



We are also led to the conclusion that a unit 

 character is represented in the germ-cell by a 



1 W. E. Castle, in Fifty Years of Darwinism (1909;, 146. 



