MAIZE BREEDING 189 



in the factor F, for variegated, to S for self-color. Emerson 

 concluded : 



"That these results favor the idea that single allelomorphic factors, 

 rather than two or more closely linked factors, are responsible for the 

 color pattern of both glumes and pericarp." 



The concluding paragraph of Emerson's 1917 paper is di- 

 rectly in line with the ideas which have been developed throughout 

 this book. With most plant-breeding material of our farm 

 crops, there is no evidence for basing a system of plant improve- 

 ment upon mutations, as these are infrequent. With anthocyan 

 color characters of corn, inherited changes sometimes occur 

 more frequently and such mutations become of selection value. 

 This does not invalidate the pure-line conception for the large 

 number of cases where factor stability is the rule. To quote 

 from Emerson: 



"The existence of the series of at least nine or ten multiple allelo- 

 morphs to which variegation belongs, indicates that a factor for peri- 

 carp color has mutated several times. Some of the factors for this series 

 have not been observed to mutate, while others have mutated rarely 

 and still others many times. In fact, the principal difference between 

 certain of the factors is thought to lie in their relative frequencies of 

 mutation." 



Podded Condition. The podded character was thought by 

 East and Hayes (1911) to be a simple dominant and to be de- 

 pendent on a single factor for its development. Extracted 

 recessives bred true to the podless condition. Collins (1917) 

 has presented evidence which indicates that the ordinary type 

 of tunicate maize represents a case of imperfect dominance and 

 that it, like the Andalusian fowls, is unfixable and related to the 

 heterozygous condition. Selfed seeds of typical podded ears pro- 

 duced three types of plants: (1) like the parent; (2) with normal 

 ears; (3) a plant which does not produce seed in the lateral in- 

 florescences but in perfect flowers in the tassels. Jones and 

 Gallastegui (1919) obtained similar results. A starchy tunicate 

 ear was used as the female parent and was pollinated with pollen 

 from a non-tunicate sweet race. The linkage between the 

 starchy and tunicate factors was quite close, only 8.3 per cent, 

 of crossing-over occurring. 



Auricle and Ligule. Emerson has shown that the absence of 

 auricle and ligule is a recessive character. In a cross between a 



