THE NATURE AND EXPRESSION OF MEN DELI AN FACTORS 139 



stead of displaying complete dominance for any one member of the 

 factor system as Shull found for the triangular capsule factors in Bursa, 

 the factors here have a certain effect in color production which is additive, 



Fio. 63. Ft squares of the checkerboard of a cross of red (RRSSTT) X white (rrsstt) 

 wheat arranged in classes according to the depth of color displayed by the phenotypes. 



i.e., two factors produce twice the depth of red coloration in the grain 

 that one produces and all six are necessary for the production of the 



