ANTHOCYANINS AND C4ENETICS 199 



At the present moment it is difficult to form any general conception 

 of the mechanism of the change which underlies bud-variation. In a 

 recent paper Emerson (629) describes the occurrence of anomalous 

 seeds of Maize (Zea), two of which are concerned with pigmentation. 

 In one, the seed was half colourless and half purple : in the other, half 

 purple and half red. He admits that the occurrence of this phenomenon 

 could be explained on the hypothesis that, subsequent to normal endo- 

 sperm fertilisation, there occurs a vegetative segregation of genetic 

 factors. But such a segregation, he maintains, cannot be typically 

 Mendelian because in neither of the cases quoted are all the genetic 

 factors (in a heterozygous condition) involved. He prefers to interpret 

 the phenomenon as a somatic mutation, that is as a change in genetic 

 constitution rather than a segregation of genetic factors. He proceeds 

 to apply this conception to the case of bud-sports in general. His 

 hypothesis in fact has already been mentioned in connection with striping 

 in Zea and Antirrhinum. In his opinion the somatic mutation may be 

 a gain of at least one new factor, the loss of a factor, or the permanent 

 modification of a factor. Against the segregation hypothesis he brings 

 the following considerations. In material homozygous with respect to 

 the Mendelian factors concerned it is not possible for bud-sports to arise 

 by segregation. Nor is it possible if a new character previously unknown 

 to the species, should arise ; nor if a dominant character appears as a 

 bud-sport in material known to be homozygous in a recessive character 

 which is allelomorphic to the dominant character in question (ex. 

 striping in Zea). If however the bud-sport be due to the loss of a 

 character, and the material be also heterozygous for the character, 

 then the case can be interpreted equally well as a segregation or a 

 mutation. 



Bateson, on the other hand, inclines to the view that bud-sports 

 are the result of somatic segregation, the sporting branches being the 

 outgrowth from cells containing one only of the segregating factors. 

 He also suggests that the phenomenon of striping may be due to the 

 fact that there is an insufficient amount of the colour factor in the 

 gametes to make the zygote self-coloured. And this may also apply 

 to some cases of pattern (see p. 190). In these cases the more intimate 

 the mixing, the more likely are the offspring to be striped, and this, 

 as we have seen, is borne out by observations upon Zea and Antirrhinum. 



