i9"] SHULL— LYCHNIS AND PAP AVER 133 



results could be explained by assuming that in those matings which 

 produced whitish-flowered offspring, the one parent possessed A, 

 the other B, while in those matings in which a fully pigmented 

 progeny was produced, the two parents had the same factor — either 

 both A or both B — or else one of them lacked both A and B and 

 the other parent lacked one of them. The occurrence of fully 

 pigmented individuals in association with " dominant whites" 

 need not then be minus-fluctuations of a single inhibitor, but 



be the result of segregation of inhibiting factors, one or 

 more of which were heterozygous in one or both parents. 



might 



Summary 



Dominant and recessive whites have been discovered in a 

 number of different plants and animals. Both the dominant 

 whites and the recessive whites may be of different kinds, though 

 externally indistinguishable. 



Dominance does not necessarily indicate presence of an added 

 gene, but when the absence of a character appears to be dominant 

 over its presence, the action of an inhibiting factor may usually 

 be inferred. An alternative hypothesis is always available, how- 

 ever, which should prevent a too dogmatic assertion that dominance 

 is synonymous with presence. 



A white-flowered form (Melandrium album) of Lychnis dioica L. 

 from Germany, when crossed with the purple-flowered form (M. 

 rubrum) from the same country, produced 23 white-flowered and 

 4 purple-flowered offspring, but in certain crosses with a white- 

 flowered strain derived from plants growing at Cold Spring Har- 

 bor, the German white-flowered plants produced purple-flowered 

 offspring in the F I? in other crosses only white-flowered offspring 

 were produced. 



In the "Shirley" poppies (Pa paver Rhocas L.), the presence of 

 a white margin of the petals is a dominant character and is probably 

 due to an inhibitor limited in its effective action to the margins 

 of the petals. 



These white margins and doubleness of the flowers are the only 

 characters in the garden poppies which were found dominant over 

 the corresponding characters of the wild type from which they 



