342 DARWINISM TO-DAY. 



vation, of persistent compilation of other men's observing, 

 and careful weighing and consideration of the data in 

 hand. In de Vries's case too there was added a large 

 amount of experimental testing of his conclusions. This 

 experimental study of the species-forming problem de 

 Vries and his followers rather seem to claim as a distinct- 

 ively new part of the basis for the mutations theory, but as 

 a matter of fact Darwin himself, in much less degree per- 

 haps, and in somewhat different manner, appealed to experi- 

 ment to test many of his conclusions. The actual forming 

 of new species by selection could not be experimentally 

 tested or proven by Darwin. Whether biologists are ready 

 to accept de Vries's pedigree-culture work and results as 

 of the same nature of rigid experimental test and proof as 

 there exists in experimentation in chemistry and static 

 physics (for that is the claim for the new "experimental 

 method" in biology) remains, perhaps, a moot point. De 

 Vries's general statement of the character and the amount 

 of the evidence on which he rests his belief in the formation 

 of species by mutation is contained in the following para- 

 graphs from his book "Species and Varieties" (p. 22). 



"Mutations are occurring from time to time in the wild 

 state as well as in horticulture and agriculture. A selec- 

 tion of the most interesting instances will be given later. 

 But in all such cases the experimental proof is wanting. 

 The observations, as a rule, only began when the mutation 

 made its appearance. A more or less vague remembrance 

 about the previous state of the plants in question might be 

 available, though even this is generally absent. But on 

 doubtful points concerning possible crosses or possible intro- 

 duction of foreign strains, mere recollection is insufficient. 

 The fact of the mutation may be very probable, but the full 

 proof is, of course, wanting. Such is the case with the 

 imitative origin of Xanthium commune Wootoni from New 

 Mexico and of (Enothera biennis cruciata from Holland. 



