222 BREEDING CROP PLANTS 



P. Segregating ratios were in accordance with the above fac- 

 torial hypotheses. Wilson (1916) obtained only white tubers 

 from selfed white-tubered varieties. Similar results have been 

 obtained by other plant breeders which show that white is a 

 recessive character. A certain amount of coloring in the young 

 sprouts or shoots, stems, and sometimes in the leaf petioles was 

 found associated with the presence of color in the tubers. With 

 regard to flower color, three white-flowered varieties, selfed, 

 produced only white flowers; and three out of four colored varie- 

 ties, when selfed, produced both colored and white forms. Color 

 is, therefore, dominant to its absence. Inheritance of this 

 character may be explained by assuming the presence of a chro- 

 mogen body and modifying factors. Heliotrope flowers are due 

 to the chromogen body plus a reddening factor; purple flowers 

 are produced by the addition of a purpling factor; white flowers 

 may be due to the absence of one or more of these factors. 

 Fruwirth (1912) found red tubers dominant over white, yellow 

 flesh over white, and lilac-colored flowers over white. It was 

 also found that different gradations of color were inherited. 



Nilsson (1912-13) found a complicated flower color inheritance. 

 A variety with violet-blue flowers gave, on selfing, progeny with 

 red, violet-blue, near-red, purple, dark and light blue, and white 

 flowers. A variety with light blue flowers, on selfing, yielded 

 progeny showing simple monohybrid segregation with white 

 recessive. Evidence that several factors were operating in the 

 inheritance of tuber flesh color was also obtained. Some of the 

 varieties with yellow flesh (tubers) bred true when selfed, others 

 segregated as dihybrids with white recessive. 



The inheritance of habit of growth was also studied. Plants 

 may be upright, bushy, or procumbent. Bushy plants are 

 heterozygous for habit of growth and many of them exhibit a dis- 

 tinct tendency to become procumbent. Homozygous forms of 

 upright and sprawling plants may be isolated easily. Period of 

 maturity is used as a means of varietal classification. It is prob- 

 ably inherited in the same manner as with other crops. 



Sterility of the anthers has been found to be a dominant 

 character. At first Salaman believed that its inheritance was due 

 to a single differential factor but later evidence indicated a more 

 complex manner of transmission. Plants producing pale helio- 

 trope flowers were found to be heterozygous for pollen sterility. 



MacDougal (1917) crossed the wild potato of Arizona, S. 



