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THE AMERICAN NATURALIST [Vol.LVI 



practicability of such a test. An observation of possible 

 importance in connection with the question of a time ele- 

 ment in mutation and with the problem of environmental 

 and physiological influences is that made by Eyster and 

 Anderson concerning the greater frequency of the non- 

 heritable (epidermal) mutations than of the heritable 

 (sub-epidermal) ones in variegated pericarp of maize. 



I have recently obtained results bearing on another 

 phase of the somatic-mutation problem as related to 

 variegated maize pericarp, namely, the relative frequency 

 of mutation of homozygous, F V, and of heterozygous, V 

 W, material. It has been shown above that the W gene 

 for colorless (white) pericarp does not mutate, so far as 

 known, when paired either with itself, W W, with the va-' 

 riegation gene, V W, or with the self-color gene, S W. 

 It will be recalled further that only one of the two homolo- 

 gous genes in homozygous variegated, F V, material mu- 

 tates at any one time. If it could be assumed that the 

 mutability of either allelomorph is uninfluenced by the 

 presence of the other, it should follow that somatic muta- 

 tions will occur with approximately twice the frequency 

 in homozygous, F F, as in heterozygous, F W, material. 

 But this expectation has not been realized. On the con- 

 trary-, both heritable (self -color) and non-heritable (dark- 

 crowm) mutations have appeared throughout all my cul- 

 tures with somewhat greater frequency in heterozygous 

 than in homozygous variegated ears. The difference has 

 been especially pronounced in very light variegated 

 strains, where mutations have appeared about two and 

 one half times as often in heterozygous as in homozygous 

 material. Even if mutations appeared with equal fre- 

 quency in heterozygous and in homozygous ears, the 

 simplex gene of the former must have a mutability of 

 about twice that of either of the. duplex genes of the 

 latter. In the very light variegated strains, therefore, a 

 simplex gene must have a mutability of about five times 

 that of a duplex gene. 



What appears to be a similar result in Mirohilis has 

 been reported by Correns (1903, 1904). Crosses of a 

 supposedly pure white race with several self-colored pink 

 yellow, and pale yellow races resulted in every case in 



