No. 565] CHANGES PRODUCED BY SELECTION 45 



Mutations may occur. We have shown the origin of 

 one family by a very wide mutation. In this particular 

 case it was not difficult to show that a constitutional 

 change took place in a single germ cell of the mother 

 plant. It was only by a lucky chance that this fact could 

 be demonstrated, for with smaller changes such proof 

 would be impossible ; but there is no reason to believe that 

 this phenomenon is unique or even rare. It is much more 

 reasonable to assume that mutations usually arise in 

 single gametes than that the same change occurs simul- 

 taneously in many germ cells. One should expect the 

 somatic result of a mutation in an hermaphroditic plant 

 — the sporting plant itself— not to breed true, therefore, 

 but to behave as an Fj hybrid between a mutating and an 

 unchanged germ cell. It is true that the mutations ob- 

 served by DeVries in (Enothera Lamarckiana are sup- 

 posed to have bred true, but this is sometimes question- 

 able even from DeVries's own data. The Lamarckiana 

 "mutants" that did breed true are much more reason- 

 ably explained as segregates from complex hybrids. 

 They can be interpreted by Mendelism with no essential 

 outstanding facts, but if they are to be interpreted as 

 mutations, several discrepancies between what actually 

 occurred and what should be expected on DeVries's own 

 theory must be explained. It must be shown why the 

 changes took place in numerous germ cells,— in both the 

 male and the female gametes— and why these germ cells 

 always fused at fertilization ; for the changed germ cells 

 must have fused with each other because many Lamarck- 

 iana plants were produced by the same mother plants that 

 produced the mutations, while the mutations are sup- 

 posed to have bred true. On the only other possible theory 

 of mutation, that the change occurred in the developing 

 zygote after fertilization, one would have to explain why 

 the mutants did not often appear as bud variations, in- 

 stead of these being much rarer than the supposed muta- 

 tions, as is actually the case. 



We do not deny the theory of mutation as modified to 



