Races which Have 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. 1 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- 
ci nil tin and some related Ericaceae. 2 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. 
2 P. ASCHERSON and P. MAGNUS, I'crhandl. d. k. k. zool.-botau. 
Gesellschaft in iricn, 1891, p. 677. 
