DE VRIES'S THEORY OF MUTATIONS. 219 



created, whereas the species had come from these, as so many local 

 deviations. 



Who would deny that Linnaeus 's work has facilitated the task of 

 those that have come after him ? Nevertheless, many species have been 

 repeatedly subdivided. We must henceforth admit that when a species 

 goes through a period of mutation, or has just gone through it, the 

 number of elementary species that keep up their independent existence 

 by the side of the parent species may be considerable, as we have seen 

 with CEnothera. And it is easily understood that a tendency arises to 

 denominate for convenience those numerous elementary species not by 

 their own names, but by a collective name. This happens in most 

 handbooks of systematic botany for well-known European plants, as, 

 e. g., Draba verna, of which not less than 200 perfectly stable ele- 

 mentary species are known, Viola tricolor, etc. 



Henceforth, however, we may no longer allow ourselves to be guided 

 by opportunism. Systematic botany will have to take her watchword 

 from physiology. De Vries has combined the qualities of the experi- 

 menter, who dares to look the physiological problem in the face, with 

 those of the systematist, who observes and appreciates with uncommon 

 sagacity the slightest shades of difference, and who with utmost deli- 

 cacy of touch sifts and deals with species and races, mutations and 

 variations. 



The elementary species are stable. Selection calls forth different 

 races within the limits of these species, but whenever selection ceases 

 the races turn back to the parent form. The maximum deviation in 

 these races is generally obtained after three or four generations of 

 continuous selection; it takes about as many generations to bring back 

 the parent form. 



It is superfluous to say that many of these phenomena must be yet 

 submitted to experimental investigation. De Vries has started this, 

 and both in the domain of fluctuating variation and formation of races 

 and in that of crossing and hybridizing he has already partly com- 

 pleted, partly only just commenced, elaborate experiments. Others 

 besides himself have of late years analyzed the phenomenon of variety 

 closely. The Cambridge zoologist, Bateson, has attempted to trace in 

 his well-known work, 'Materials for the Study of Variation,' what it 

 really is that variability offers towards the making of species, both in 

 the most different species of animals and with respect to their divergent 

 organs. He has, however, not seen his way out of the labyrinth, and 

 although he came to the conclusion that it is not fluctuating variability 

 which presides over the formation of species, but that a discontinuity 

 must necessarily play a part, yet he, too, has committed himself to the 

 assumption that the determination of the width of the fluctuations 

 can furnish us with valuable data for understanding the gradual forma- 



