Heredity Studies in the Morning-Glory 21 



behavior of color types in crosses 



Under this heading is considered the behavior of each type separately 

 when crossed with the other types. 



Type 1 White (Plate II) 



White crossed with pink. — Two crosses are recorded between white 

 and pink. Cross 132 has already been discussed (page 19). In the 

 other cross, 169, the Fi consisted of 2 whites and i light blue. This 

 might be expected if a pink (CCRR) were crossed with a white that was 

 simplex for both B and X (CCrrBbXx). Plant 169-3, the light blue 

 (hypothetical ly CCRrBbXx), was selfed and gave i mauve and i white. 

 If it had produced more offspring, light blues, mauves, pinks, tinged 

 whites, and whites would all have been expected to make their appearance, 

 due to the recombinations or dropping-out of these various simplex genes. 



White crossed with mauve. — In cross 121 there were only two Fi plants 

 and both were mauves. This result might have been obtained if a mauve 

 containing I (instead of X) were crossed with a white lacking both B 

 and I and with or without X. Such a cross would give only mauves. 



The Fi of cross 108 consisted of 5 light blues, which split up into an 

 F2 of dark blues, light blues, and whites. Had larger nimibers been ob- 

 tained , the rarer genotypes for mauve and pink might have been expected 

 to appear. This cross may be explained on the assumption that the white 

 parent brought in the gene B. The Fi plants, then, would be all light 

 blues, and simplex for both R and B but either simplex or duplex for X. 



The only other cross between a white and a mauve was cross 125. 

 It gave I light blue and i light purple. The mauve parent, however, 

 was recorded in the greenhouse during the first year of the experiment, 

 when the author was not so familiar with behavior of types as he became 

 later. It was probably a withered dark blue, because when selfed it 

 threw 20 dark blues and no others. For this reason it is more probable 

 that this parent brought in the gene B than that the white parent carried it. 



White crossed with magenta. — Four crosses were made between white 

 and magenta. In the Fi from these crosses there appeared magentas, 

 mauves, and pinks. The significant feature of this fact is that no types 

 higher in the scale than magenta appeared, except in cross 209, in which 

 case the white parent must have contained the gene B. It had light 

 blue sibs out of a white parent selfed. It should be noted also that no 

 tinged whites nor whites appeared, which is to be expected on the sup- 

 position that magenta contains both C and R in duplex condition. 



In cross 129 the single Fi plant obtained gave, when selfed, 3 whites 

 and I mauve. This might occur if the white parent lacked only the gene 



137 



