VAKIATIOX AND IIKKEDITY 9 



cun'^e — not the result of iiiodilieatioiial effects — may viv- 

 idly bring- home the fact that the species is dividing into 

 two sub-species. " "^ Tlius, by means of statistics, which 

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

 species being born under our very eyes. 



The point we have just made shows how a species 

 might originate by the accumulation of extremely slight 



Figure 2. Curve of Distribution. 



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

 ganic structure may ]iass with seeming abruptness from 

 one position of equilibrium to another." Changes of con- 

 siderable amount sometimes occur at a single lea)). 

 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- 

 otlier ])y discontinnons lea])s and bounds as opposed to 

 the continuous process. He therefore l)eliev(^s that 



8 Thomson & Goddcs, op. cil., p)). l'Jl-li2'2. 



