VARIATION AND HEREDITY 125 



it will tend to re-establish itself, but if the 

 range is overpassed, it will topple over into 

 a new position; also that both of them are 

 more likely to topple over towards the posi- 

 tion of primary stability than away from it." 



THE MUTATION THEORY. In 1900 Professor 

 Hugo de Vries of Amsterdam published under 

 the title " The Mutation Theory " an account 

 of his very interesting and important experi- 

 ments and observations on the origin of 

 species in the vegetable kingdom. The most 

 striking of his conclusions was that species 

 arise from one another by discontinuous 

 leaps and bounds, as opposed to a continuous 

 process. Whereas Darwin relied on the action 

 of selection on minute individual variations 

 or fluctuations, de Vries believes that these 

 have nothing to do with the origin of species, 

 which appear " all at once " by mutations. 

 Let us quote some of his characteristic state- 

 ments. 



"Jy the mutation theory I mean the 

 proposition that the attributes of organisms 

 consist of distinct, separate and independent 

 units. These units can be associated in groups, 

 and we find, in allied species, the same units 

 and groups of units. Transitions, such as 

 we so frequently meet with in the external 

 form both of animals and plants, are as 



