256 Emerson. 



If bud sports occur in material that can be shown to be homo- 

 zygous with respect to the Meudeliaii factors concerned, such sports can 

 not be due to a segregation of factors but must be instances of somatic 

 mutation. At present there is little evidence that bears directly upou 

 tills problem. It usually happens that in the rare cases in which bud 

 sports are observed the material is not subjected to Mendelian analysis, 

 so that it cannot be said whether it is homozygous or heterozygous for 

 the factoi-s concerned. 



If progressive changes occur as bud sports, that is, if new charac- 

 ters not previousl}' known in the species so arise, it would seem rea- 

 sonable to conclude that somatic mutations rather than segregations 

 are responsible. It is not, however, my purpose here to examine any 

 number of bud sports with a view to deciding, if that were possible, 

 whether or not new characters have arisen in this way. It should be 

 noted, nevertheless, in passing that many bud sports seem to be due 

 to the loss of some factor, as pointed out by East (6, 7). Such cases 

 can be interpreted equally well as segregations or as mutations, provided 

 no Mendelian analysis of the material has been made. 



If a dominant character appear as a bud sport, in material known 

 to be homozygous with respect to a recessive character that is allelo- 

 morphic to the dominant character in question, it seems clear that a 

 somatic mutation is the responsible agent. In some instances the pro- 

 duction of a dominant self-color pattern as a bud sport from variegated 

 plants seems to be of this nature. In a recent paper (Emerson (12)) 

 I have discussed the inheritance of a somatic variation in the pericarp 

 of variegated maize and have interpreted it as a somatic mutation. 



.Self-color in the pericarp of maize is a simple dominant to varie- 

 gated pericarp. Occasionally a plant that is homozygous for variegated 

 pericarp may produce some self-colored seeds, just as certain variegated 

 leaved plants (Mimbilis for instance) may produce a wholly green 

 brancli. Such self-colored seeds frequently produce in turn plants with 

 self-colored instead of variegated ears. And these self-colored ears be- 

 have like Fl ears of a cross between variegated and self-colored races. 

 In sliort, a bud sport in a liomozygous plant is inherited in a strictly 

 Mendelian fashion. Such a bud sport could hardly be the result of a 

 segregation of factors. 1 liave therefore interpreted it as a somatic 

 mutation — the change of a variegation factor into a self-color factor. 



Even though the variegated-eai-ed parent plant be heterozygous, in- 

 stead of homozygous, for pericarp color, the somatic variation frdm 



