May 12. 1910] 



NA TURE 



305 



cuie must admire the patience and enthusiasm which 

 he has brought to the task, and if the naturalist must 

 be permitted to criticise the result from his point of 

 view, he cannot but approve the scrupulously fair and 

 instructive way in which de Vries has published every 

 detail cf his research. 



In order to do justice to the theory which de 

 Vries has founded on his observations, it is necessary 

 to attach some precise meaning to the technical terms 

 used. Darwin was nothing if not a naturalist. It is 

 impossible to read de Vries 's pages without feeling 

 that he is not quite at his ease with the naturalist's 

 technique. On p. 21 I find, for example, the follow- 

 ing statement : — 



"It is most remarkable that in the * Index 

 Kewensis,' which was published at Darwin's expense 

 after his death, no distinction is drawn between varie- 

 ties and synonyms." 



I do not suppose it was intended, but this might be 

 construed to mean that the work as executed failed 

 to carry out Darwin's intention. That this would be 

 the reverse of the fact I can state with confidence, as 

 the plan was discussed and settled between Mr. Dar- 

 win' and myself in his own house. What he told me 

 he wanted was to be able to trace to its source any 

 specific name that he met with. This the " Index " 

 does, and it is an incalculable boon to those who use 

 it. But its purpose is merely bibliographical, and it 

 was not intended to express any opinion as to the 

 validity of the species which it catalogues ; nor was 

 there ever any suggestion that it should catalogue 

 varietal names. 



14: would be quite possible for a discussion of de 

 Vri«s'g theory- to evaporate into a mere logomachy, a 

 mere dispute as to the meaning of words. That I 

 hope to avoid, but if I fail, he himself will have 

 to share the blame. The word " mutability," which is 

 peculiarly de Vries's property, and, indeed, contains 

 the kernel of his theory, is an example. So far as I 

 caa -find, it does not occur in Darwin's writings. Yet 

 on p. 202 I find the following summarj- of the Dar- 

 winian theory : — 



" Mutability may take place in almost all directions ; 

 and' it is natural selection which operates in one 

 direction during long geological periods " ; 



and that there may be no mistake, he adds that this 

 "obviously represents the view of Darwin." This is 

 emphasised on p. 198, where " species-forming varia- 

 bility " and "mutability" are treated as synonyms. 

 But;de Vries's whole contention is that, in the or- 

 dinary acceptance of the terms, they are profoundly 

 different. This is apparent from the following 

 passage in the author's "Plant Breeding" (pp. 5-6), 

 a book which, I confess, seems to me to be written 

 with more precision that the larger one. 



**The phenomena that follow Quetelet's law aro 

 now considered as one group, which is called fluctua- 

 ting variability or fluctuation, since the individual 

 qualities fluctuate around their average. The pro- 

 cesses b\' which new qualities are produced must be 

 studied separately. Under the assumption that these 

 processes are neither slow nor invisible, but consist 

 in -leaps and jumps such as are popularly indicated 

 by the name of sports, they are now called mutations, 



NO. 21 15, VOL. %-T^ 



and the great subdivision of the phenomena of varia- 

 bilitv is designated, in consequence thereof, as muta- 

 bility." 



Now there is no want of precision about this state- 

 ment. It of course assumes the very f>oint which 

 has to be proved, that " fluctuating variability " does 

 not produce " new qualities " ; but that is another 

 story. 



De Vries has elsewhere employed the words con- 

 tinuous and discontinuous, as descriptive of the two 

 processes. Unfortunately, Bateson used these at the 

 same time in a different sense, and this has added 

 another pitfall to the discussion of the subject. .At 

 first sight we seem to have a sharp distinction be- 

 tween the theories of Darwin and of de Vries, the 

 one accounting for the origin of species b}- the accumu- 

 lation of small variations, the other by "sports." If 

 we take, as an example of the latter, the production 

 of the nectarine from the peach, there can be no doubt 

 that the leap may be considerable. While the occur- 

 rence of sports is undeniable, de Vries appears to draw 

 a distinction between the part attributed to them by 

 Darwin and Wallace in the production of species 

 (pp. 12 and 39). Wallace regards them "as absolutely 

 without significance " (p. 40). But Darwin, with 

 more caution, doubts whether they "are ever perma- 

 nentlv propagated in a state of nature " (" Origin." fifth 

 edition, p. 49'), and this is practically the same thing. 

 De Vries himself is led gradually to minimise their 

 magnitude. He finds (p. 53) "sports" "not a happy" 

 term, and prefers "jerky variability" where "jerks 

 mav only induce quite small changes." Later on he 

 finds (p. 55) that " many mutations are smaller than 

 the differences between extreme variants." He 

 quotes Galton's polyhedron which, when disturbed, 

 "oscillates round its position of equilibrium " (fluctua- 

 tion), and finally "comes to lie on a new side " (muta- 

 tion). But when the faces are ven>- small, the illus- 

 tration is obviously not helpful ; when the variation 

 is verv small, the distinction between the two kinds 

 is inappreciable. 



To meet this difficulty, de Vries sets up other criteria. 

 These he has drawn from a mass of experimental 

 work for which it is impossible to conceal one's 

 admiration, and is a {wsitive addition to our 

 knowledge. But it is, of course, permissible to draw 

 from it somewhat different conclusions. "Mutants" 

 arise without transitional forms (p. 248). It appears, 

 however (p. 504), that such do occur, but simul- 

 taneously, and not before ; the mutants, therefore, are 

 artificially selected from a varying population. But 

 they possess from the first absolute stability; this is 

 an extremely interesting point ; it is, of course, 

 irnplied that they were self-fertilised, and that the 

 conditions were unchanged. It is, however, to be 

 noticed that it was not universally the case, as three 

 of- the mutants studied "proved to be inconstant," 

 and some actually reverted to the original parent 

 Cp. 508). Such mutants he calls "elementary species," 

 a term for which he invokes (p. 57) the authority of 

 Darwin, who, however, only said that "varieties are 

 incipient species," a very different thing. 



It follows ■ that " specific characters are absolutely 



