242 BREEDING CROP PLANTS 



shell beans may be thrashed is of economic importance. In this 

 group, color, size, and shape of seeds are usually included in 

 varietal descriptions. Both productivity and disease resistance 

 may differ strikingly in different varieties of beans. 



Inheritance. Seed-coat color has been shown by Shaw and 

 Norton (1918) to involve several factor differences. The work 

 was carried on with twenty-one varieties including more than 

 40,000 plants. Crosses between mottled and self-colored varie- 

 ties yielded mottled beans in FI and showed 3 : 1 ratios in F<^. 

 Mottled X white varieties gave mottled in FI, and in F z the ratio 

 of 9 mottled to 3 self-colored to 4 white usually resulted. It was 

 demonstrated that pigment patterns and pigment colors were 

 controlled by distinct factors. All plants with white or eyed 

 beans bore white flowers while plants with mottled or self-colored 

 beans usually bore pink flowers. 



The inheritance of stature in beans, as in peas, is in some crosses 

 dependent on a single factor difference while in other crosses 

 several factor differences are involved. Emerson (1916) has 

 explained the result of crossing a tall pole (indeterminate growth) 

 bean and a short bush (determinate growth) bean or a short 

 pole bean and a tall bush bean, by a three-factor hypothesis. The 

 following values to be added to an initial value of three inter- 

 nodes were assigned to the factors : Factor A either homozygous 

 or heterozygous added 10 internodes approximately, while fac- 

 tors B and C each added two internodes when homozygous and 

 one when heterozygous. Results were explained factorially 

 as follows: 



Parent 1 AABBCC = 17 internodes or AAbbcc = 13 internodes 



Parent 2 aabbcc = 3 internodes or aaBBCC = 7 internodes 



FI AaBbCc = 15 internodes or AaBbCc = 15 internodes 



Many new forms would naturally be produced in F%. 

 Tschermak (1916) has brought together and summarized the 



FIG. 60. Flower structure of bean. 



1. Small branch showing a, developing pod; b, c, flowers in different stages of 

 development. 



2. Front view of fully opened flower a, calyx; b, wing; c, standard; d, keel. 



3. Enlarged keel. 



4. Keel with outer part broken away to show 6, style; c, anther; d, undevel- 

 oped pod; e, ovary. 



5. 6. Longitudinal and cross section of pod. 



7. Enlarged stigma showing a, stigma hairs. 



8. Anther. 



Size: 1, n; 2, about 2w; 3 to 8, greatly enlarged. 



