SEED COAT COLOR IN GARDEN BEANS. 



67 



The Inheritance of Pigment Patterns. 



The disposition of pigments over the surface of the bean may be even, 

 in which case we call it self-colored; or the pigments may be irregularly 

 disposed, revealing the separate colors in short stripes or splashes, when 

 we have a mottled bean. The mottling or the self-color may be limited 

 to a more or less well-defined area around the hilum, giving us an eyed 

 bean. These two pigment patterns, mottling and eyedness, will be 

 separately considered. 



Mottling. 



There are many varieties of beans with mottled seeds. The colors 

 involved are various, and the type of mottling differs in different varieties. 

 The inheritance of the various colors is dealt with in a later section. The 

 various types of mottling are without difficulty separated into two classes, 

 — a light mottling shown in various varieties of the Horticultural class, 

 and a dark mottling shown by Red Valentine, Refugee and many others. 

 Many crosses involving both types of mottling have been made, and the 

 mottling always breeds true. There are also many crosses where only 

 non-mottled parents have yielded mottled beans, both of the light and 

 dark mottled types. But in no case have these mottled beans bred true. 

 This is in accord with other investigations, and a theory to account for 

 the facts has been set forth by Emerson (4) on the suggestion of Spillman. 

 This theory supposes that mottling is brought about by two factors, 



Y and Z, which are coupled in the case of true-breeding mottled varieties, 

 but may be separately borne by distinct varieties, and in such cases are 

 inherited independently. Individuals from such crosses bearing both 



Y and Z are mottled and always heterozygous, while those bearing either 

 one are not mottled. Whether or not this is the final and complete ex- 

 planation of mottling in beans, it serves to explain the results thus far 

 obtained. 



The following crosses of mottled beans have bred true, yielding only 

 mottled progeny: — 



