MUTATIONS 



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rably associated with variegation. Correns has pointed out that 

 variegated Mirabilis plants cannot be considered mosaics of green and 

 'chlorina' types due to heterozygosis, since they do not segregate into 

 chlorina and green, but into variegated and green. The same reasoning 

 applies to variegation in the color of maize ears. Variegated-eared plants 

 do not throw reds and whites, but reds and variegates. The conclusion 

 seems irresistible that self-color occurring as a somatic variation is 

 due to the change of a Mendelian factor for variegation into a factor for 

 self-color. If this be granted, the behavior of these variations in later 

 generations is a mere matter of simple Mendelian inheritance." 



If bud sports are caused by mutations and if most bud sports involve 

 a change from the dominant to the recessive condition of a certain factor, 

 it follows that the change in chemical constitution must affect both of the 



Fia. 112. Bud sport and chimera in an ear of corn. This ear appeared in a field of 

 white dent corn. The apparently white kernels, occupying about J of the surface, were 

 actually variegated, being marked with "fine red lines, or streaks, radiating from the caps 

 down the sides of the kernels." (sifter Hartley.) 



duplex factors present in the somatic cell in order that the recessive 

 character may appear. To those who think of mutations as fortuitous 

 events, this may seem an obstacle to the conception that bud sports 

 are the result of factor mutations. But from the point of view that 

 factor mutations are caused, probably by some specific internal condition, 

 it would seem most natural for the cause to have the same effect on both 

 factors. Obviously this conception assumes that in such cases the specific 

 cause, whatever it is, has the same potentiality in all parts of the nucleo- 

 plasm, and there is no a priori logical objection to such an assumption. 

 At the same time there is good evidence that mutations do sometimes 

 occur in only one of a duplex pair of factors. Hartley reports "a remark- 

 able ear (Fig. 112) occurring in a field of white dent corn which had 

 for many years been grown as a reasonably pure corn, but which occa- 

 sionally, as many white corns do, produced a red ear." But this ear was 

 only partly red since about one-fifth of its surface was occupied by varie- 

 gated grains which appear to be white in the picture. Hartley tested 

 all the grains on this ear and found thai the red grains produced 

 a crop of 84 red ears and 86 pure white ears, while the variegated grains 



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