Mat 4, 1906.] 



SCIENCE. 



683 



led him, as was stated, to this conclusion. 

 He then conceived the idea of searching in 

 nature for a species in a state of mutation. 

 The story of his discovery of mutating in- 

 dividuals of Lamarck's evening primrose, 

 CEnotliera lamarchiana, in the vicinity of 

 Hilversum, Holland, need not be repeated. 

 From specimens of this species he obtained 

 by pedigree cultures seven new forms, six 

 of which he has described as new species 

 and one as a new variety. Besides this 

 experimental evidence in favor of his 

 hypothesis, de Vries compiled a large 

 amoimt of data that give additional weight 

 to his conclusion. 



These are the three principal hypotheses 

 attempting to account for the origin of 

 new species. I think that it is not neces- 

 sary to give a special discussion of isola- 

 tion as a factor in evolution, as it does not 

 affect the validity or invalidity of any one 

 of the hypotheses stated. Isolation is a 

 passive, not an active factor; its impor- 

 tance, however, is beyond question. 



On the leaf following the title page of 

 'Species and Varieties, their Origin by 

 Mutation,' are three quotations: 



'The origin of species is a natural phe- 

 nomenon. ' — Lamarck. 



'The origin of species is an object of 

 inquiry. '—Darwin. 



'The origin of species is an object of 

 experimental investigation. '-De Vries. 



The history of any movement of thought 

 is always from a greater or less indefinite- 

 ness to greater definiteness and precision. 

 The solution of any complicated problem 

 mvist be preceded by the analytical work 

 that discovers the factors involved. 



The following will indicate the tenden- 

 cies and stages of such a movement : 



1. The accumulation of data, largely 

 through mere curiosity. 



2. An attempt to discover some causal. 



relation underlying the phenomena, and 

 the propounding of an hypothesis. 



3. The energetic accumulation of addi- 

 tional data, especially to controvert or 

 sustain the hypothesis already propounded. 



4. A critical reexamination of the ac- 

 cumulated data to discover if they are sus- 

 ceptible of a different interpretation, or if 

 there may not be some previously undis- 

 covered underlying principle. 



5. The announcement of a different in- 

 terpretation or a new principle will pro- 

 duce additional activity both in the accu- 

 mulation of data and in the attempts to 

 interpret them. 



6. There will be recurrent periods of the 

 accumulation of facts with reference to old 

 theories, and a continual critical reexamina- 

 tion both of facts and of theories. These 

 will lead to a more highly developed crit- 

 ical faculty and more refined methods of 

 research. 



Previous to Lamarck there were a num- 

 ber of zoologists and botanists energetic- 

 ally recording their observations, especially 

 as a result of the classification and system 

 of nomenclature proposed by Linnaeus. 

 Lamarck proposed the theory of evolution 

 that has been revived by the neo-Lamarck- 

 ian school. Darwin correlated the data 

 previously accumulated, supplemented by 

 a stupendous number of observations of 

 his own, and gave us his 'Origin of Spe- 

 cies.' The accumulation of data has con- 

 tinued, and the critical examination of 

 previously announced conclusions becomes 

 more acute. With this more highly de- 

 veloped critical faculty have come addi- 

 tional methods of investigating the prob- 

 lems of evolution. 



De Vries 's book, 'Species and Varieties, 

 their Origin by Mutation,' contains not 

 only a vast body of highly important facts, 

 but is pregnant from cover to cover with 

 suggestions regarding important lines of 



