No. 642] 



NATUBE OF BUB VARIATIONS 



71 



plants with strongly red-striped flowers and with numer- 

 ous self red flowers or even whole branches of such 

 flowers. Intercrosses of the pink and yellow races gave 

 only self-colored progeny, from which fact it was con- 

 cluded that the white-flowered race carried a latent factor 

 for striping. It was later discovered that about three 

 per cent, of the flowers of the white race showed minute 

 flecks of red. It w^as evidently an extremely light, varie- 

 gated race, rarely if ever throwing somatic self-color 

 mutations when the variegation gene was duplex (homo- 

 zygous material) but producing such mutations with con- 

 siderable frequency when that udic was simplex (hetero- 

 zygous material). Correns coiicliKU'd that red variega- 

 tion of Mirabilis flowers is a character that, with self- 

 fertilization or inbreeding, remains almost completely 

 latent, but which, through the entrance of foreign germ 

 plasms, is brought to full expression. 



If the mutability of a gene can be increased through 

 the influence of some modifying factor or factors brought 

 into combination with it by crossing, as suggested by 

 Correns, it should be possible to discover crosses that 

 would not produce the effects so far observed in Zea and 

 Mirahilis. While the problem deserves much more study 

 from this viewpoint, it seems unlikely that results with 

 maize can be explained on any such liasis, unless the 

 postulated modifyiim- I'lwtor is the allelomorph of the 

 variegation gene or snun' tactor vitv closely linked with 

 it. It must be noted in tliis (MMiiieeti.m that the e.niipari- 

 son in maize was ma.l(> hetw.vn homozygous and hetero- 

 zygous variegated ears .)f th.' same F, progenies grown 

 from self-pollinated T, heteiczygotes-a circumstance 

 that would afford abundant opportunity for recombina- 

 tions of independently inherited modifying factors. That 

 the differences in mutability noted in maize may be due 

 to differences in the interaction of like as contrasted with 

 that of unlike allelomorphs, as suggested by Anderson 

 and Dt inei-ee, is a somewhat novel conception worth care- 

 ful consideration if means can be devised for subjecting 

 it to a crucial test. 



Before the topic of somatic mutation is dismissed, it 

 should be noted that the phenomenon is not limited to 



