88 



SCIENCE. 



[N. S. \ OL. XXIV. No. 603. 



its use Avould be rather to destroy than to build 

 up. But besides this negative result there is a 

 positive result too, and the same discontinuity 

 which in the old structure had no place may be 

 made the framework round which a new structure 

 may be built.°^ 



And the following cautious statement from 

 Darwin : ' We are led to conclude that species 

 have generally originated by the natural selec- 

 tion, not of abrupt modifications, but of ex- 

 tremely slight differences.' " Their origina- 

 tion by the natural selection of the ' abrupt 

 modifications ' is rejected, among other rea- 

 sons, because " we have no evidence of the 

 appearance, or at least of the continued pro- 

 creation, under nature, of abrupt modifica- 

 tions of structure." ^ Since the work of de 

 Vries the last statement no longer holds true. 



The critic " is unable to see where he [de 

 Vries] draws the line between variations * * * 

 and mutations." The following quotation seems 

 written in anticipation of that statement : 

 " The relation between mutability and fluctu- 

 ating variability has always been one of the 

 chief difficulties of the followers of Darwin.°* 

 The majority assume that species arise by the 

 slow accumulation of slight fluctuating devia- 

 tions, and the mutations are only to be con- 

 sidered as extreme fluctuations, obtained, in 

 the main, by a continuous selection of small 

 differences in a constant direction." 



" My cultures show that quite the opposite is 

 the fact. * * * Oscillating changes have noth- 

 ing in common with the mutations." ^ " Muta- 

 tions are going on in all directions, producing, 

 if they are progressive " (they are not all 

 alike), "something quite new every time. 

 Fluctuations are limited to increase and de- 

 crease of what is already available." " 



One point is stated with terse accuracy: 

 de Vries has not only not ' solved the old 

 sophistic problem of how much must be added 



"Bateson, I. c, p. 568, 1894. 



" ' Animals and Plants Under Domestication,' 

 p. 495. Italics mine. 



'^ Darwin, I. c, p. 495. 



^° ' Species and Varieties,' p. 7. Even Wallace 

 had this difficulty. Ibid. 



*" ' Species and Varieties,' pp. 568-569. Cf. pp. 

 715, 718 and 459. 



"'Species and Varieties,' p. 719. 



to a small thing to make it a large one,' but has 

 clearly demonstrated, in his lecture on ' The 

 Origin of the Peloric Toad-Flax' that, so far 

 as the origin of species is concerned, the 

 problem is incapable of solution. 



The discoverer of ' the fallacy of the muta- 

 tion theory ' tells us that mutations have been 

 observed chiefly among domestic forms. If 

 this were true, the suggestion is, not to reject 

 mutation on this account, but to initiate ex- 

 tensive experiments among a wide systematic 

 range of wild plants (and of animals also), and 

 see if what now appears to be the case is in 

 reality a general truth, or only an expression 

 of limited experience. 



We are told ^^ that if de Vries should ' claim 

 that species could be made out of mutations, 

 he would be right.' Well and good. The 

 quotation"' has already been given. Elemen- 

 tary species ' are combined into species * * *.' 



If the rarity of mutations" seems to be a 

 stumbling-block toward accepting them as the 

 material on which natural selection may oper- 

 ate, it will be wholesome to recall that the 

 formation of new specific groups (species of 

 the systematists) is far more rare in nature 

 than in the writings of systematic botanists 

 and zoologists. 



Mutation has, indeed, ' always ' °° been re- 

 garded as a special form of variation, and so 

 it is in ' Species and Varieties,' notably in 

 lecture I., and throughout the entire book. 

 But if ' Consequently, nothing is left of de 

 Vries's mutation theory but the bare facts 

 represented by his experiments,' science has 

 been munificently enriched thereby, to say 

 nothing of the new method of research in the 

 study of evolution, entirely ignored by the 

 above statement, and the contribution for 

 which science is de Vries's greatest debtor. 



" To my mind," says de Vries, " the real 

 value of the discovery of the mutability of the 

 evening-primrose lies in its usefulness as a 

 guide for further work." 



I may repeat, in closing, what was stated in 



^^ Ortmann, I. c, p. 747. 

 ^ From ' Species and Varieties,' p. 459. 

 ** Ortmann, I. c, p. 747. 



" That is, since the process has been recognized 

 and described. 



