Races which Hai'c Arisen Suddenly in Nature. 95 



§ 10. INSTANCES OF RACES WHICH HAVE ARISEN 



SUDDENLY IN NATURE. 



In nature, elementary species are, as is well known, 

 not connected with their closest allies by transitional 

 forms. Nevertheless fluctuating and transgressive varia- 

 bility frequently bring about the appearance of contin- 

 uous series, which however on closer examination espe- 

 cially by statistical methods dissolve into perfectly dis- 

 tinct component units. ^ In very many cases these tran- 

 sitional forms are absolutely lacking, and the separation 

 of a particular form as variety, subspecies, elementary 

 species, or even species, is mainly founded on their ab- 

 sence. 



The absence of transitional stages in the case of forms 

 which have been long familiar and are widely distributed 

 obviously tells little concerning their mode of origin. 

 Results are more likely to follow from the investigation 

 of those cases in which the types in question are local 

 in occurrence and in which, therefore, if transitional 

 stages should occur, one would expect to find them in the 

 locality inhabited by the plant. In some instances an 

 exhaustive and minute study of the geographical distribu- 

 tion of certain varieties has led to the discovery of the 

 center from which distribution took place. Ascherson 

 and Magnus obtained a result of this kind with the 

 pale fruited varieties of the European species of Vac- 

 cininni and some related Ericaceae.^ In inquiries of this 

 kind, the absence of transitions at the present time points 

 to the conclusion that they may never have existed. 



' See Vol. I, Part II, § 25, p. 430. 



^ P. Ascherson and P. Magnus, J'ciiiaiidl. d. k. k. zooL-hotan. 

 GcscUschaft in JVicn, 1891, p. 677. 



