VARIATION AND HEREDITY 9 



curve not the result of modificational effects may viv- 

 idly bring home the fact that the species is dividing into 

 two sub-species. Thus, by means of statistics, which 

 seems the dryest of all methods, we are able to see a 

 species being born under our very eyes. 8 



The point we have just made shows how a species 

 might originate by the accumulation of extremely slight 



FIGUBE 2. Curve of Distribution. 



variations. But evidence is at hand to show that or- 

 ganic structure may pass with seeming abruptness from 

 one position of equilibrium to another. Changes of con- 

 siderable amount sometimes occur at a single leap. 

 These sudden jumps or changes are called "discontinu- 

 ous variations," or sometimes, "sports," and, in certain 

 cases, "mutations." Professor Hugo de Vries has made 

 some very interesting and important experiments and 

 observations on the origin of species in the plant king- 

 dom. He found that species often arise from one an- 

 other by discontinuous leaps and bounds as opposed to 

 the continuous process. He therefore believes that 



s Thomson & Geddes, op. cit., pp. 121-122. 



