104 THE THEORY OF MUTATIONS 



so to speak, from the main stem, and are not neces- 

 sarily advances or regressions ; that they attain 

 their full constancy at once, and that they exhibit 

 just the same fluctuations and variations as the 

 older species have. " But," he says (p. 569), " such 

 oscillating changes have nothing in common with 

 the mutations. Their essential character is the 

 heaping up of slight deviations round a mean, and 

 the concurrence of continuous lines of increasing 

 deviations, linking the extremes with this group. 

 Nothing of this kind is observed in the case of 

 mutations. There is no mean for them to be 

 grouped around, and the extreme only is to be 

 seen, and it is wholly unconnected with the original 

 type. It might be supposed that on closer inspec- 

 tion each mutation might be brought into some 

 connexion with some feature of the fluctuating 

 variability. But this is not the case." 



Take, for example, the dwarf form of CEnothera. 

 This is a distinct species. But there are larger and 

 smaller forms of the ordinary (Enothera. No doubt, V 

 but the small forms never approach 7Ke"size of 

 the dwarf species. There is always a gap ; and, 

 what is more, the small examples of the ordinary 

 species are weaklings whilst the dwarf species 

 itself is remarkably robust. 



It will be remarked that the observations on 

 which de Vries' theory is founded are entirely 

 drawn from the plant world ; and so far no one, 

 we believe, has pointed out any similar occurrences 

 in the animal kingdom. On the transformist hypo- 

 thesis, however, the two are continuous, and what 

 one finds in the one should be discoverable in the 



