Heredity Studies in the Morning-Glory 23 



Tinged white crossed with dark blue. — In cross 151 the Fi progeny 

 consisted of 2 dark blues and 4 light blues. In the next generation the 

 two dark blues produced 9 dark blues and 2 mauves, while the light blues 

 broke up into dark blues, light blues, mauves, tinged whites, and whites, 

 as was to be expected. The tinged white parent must have carried the 

 gene X, otherwise no dark blues could have appeared in the Fi. Such 

 a cross may be represented as follows: 



CCRRBBXX dark blue f „^^^ f XX dark blue 



RRBb 



X cc 



CCRrbbXx tinged white 



\ Xx light blue 



In cross 159 the tinged white parent was a sib of the one used in cross 151. 

 The two Fi plants were recorded as "very pale blue or tinged white," 

 showing that they contained the gene B and belonged to the light blue 

 type rather than to the tinged white of the red series. This is further 

 shown by their behavior when selfed. They gave 3 light blues, i tinged 

 white, and 11 whites. None of the red series here made its appearance. 

 Assuming a cross between a tinged white of the same constitution as the 

 one used in cross 151 and a dark blue that is simplex for X, the Fi would 

 contain very pale blues of the constitution CCRrBb which would throw 

 light blues, tinged whites, and whites, as in cross 159. 



Type 3 Pink (Plate I) 



Pink crossed with purple.— Since purple is due to several genes super- 

 posed upon the pink type, it might be expected to be epistatic to pink. 

 So it was found to be in the two crosses recorded between pink and purple. 

 The purple parents were sibs, as were also the pink parents. Cross 175 

 gave an Fi progeny of i dark purple, while cross 176 gave 4 light purples, 

 which were almost dark. The F2 progeny from these crosses consisted 

 of purple, dark blue, magenta, mauve, and pink types. 



Such behavior is to be expected in a cross between a homozygous dark 

 purple and a homozygous pink. The Fi would consist of purples that 

 would split up into all the hypostatic types except tinged white and 

 white, these two types appearing only where R is simplex or nulliplex. 



Type 4 Mauve (Plate I) 



Mauve crossed with magenta. — Crosses 128, 203, 205, 206, and 208 

 were all made between magentas and pinks, and in every case the Fi 

 plants were all magentas. When selfed, these Fi magentas gave an 

 F2 progeny comprising magentas, mauves, and pinks. 



139 



