No. 642] VAEIATION IN INDIVIDUAL GENE 



45 



ably very much more— before half of them became 

 changed. This puts their stability about on a par with, 

 if not much higher than, that of atoms of radium— to use 

 a fairly familiar analogy. Since, even in these latter ex- 

 periments, many of the mutations probably occurred 

 within a relatively few rather highly mutable genes, it is 

 likely that most of the genes have a stability far higher 

 than this result suggests. 



The above mutation rates are mere first gleanings — we 

 have yet to find how different conditions affect the occur- 

 rence of mutations. There had so far been only the 

 negative findings that mutation is not confined to one 

 sex (Muller and Altenburg, 1919; Zeleny, 1921), or to any 

 one stage in the life cycle (Bridges, 1919; Muller, 1920; 

 Zeleny, 1921), Zeleny 's finding that bar-mutation is not 

 influenced by recency of origin of the gene (1921), and 

 the as yet inconclusive differences found by Altenburg 

 and myself for mutation rate at different temperatures 

 (1919), until at this year's meeting of the botanists 

 Emerson announced the definite discovery of the influence 

 of a genetic factor in corn upon the mutation rate in its 

 allelomorph, and Anderson the finding of an influence 

 upon mutation in this same gene, caused by developmental 

 conditions — the mutations from white to red of the mu- 

 table gene studied occurring far more frequently in the 

 cells of the more mature ear than in those of the younger 

 ear. These two results at least tell us decisively that 

 mutation is not a sacred, inviolable, unapproachable 

 process : it may be altered. These are the first steps ; the 

 way now lies open broad for exploration. 



It is true that I have loft out of account liere the re- 

 ported findings by several itivotiuatoi-s. of ucnetic vari- 

 ations caused by treatiiicnts witli \ arioiis toxic substances 

 and with certain other uinisua! conditions. In most of 

 these cases, however, the claim has not l)een made that 

 actual gene changes have been caused: the results have 

 usually not been analyzed genetically and were in fact 

 not analyzable genetically; they could just as well be 

 interpreted to be due to abnormalities in the (li-tril)uti()n 

 of genes — for instance, chromosome al)noi inalitics like 



