Heredity Studies in the Morning-Glory 19 



dark blue, light blue, mauve, pink, tinged white, and white. Many of 

 these genotypes would be very slightly different from others, and the 

 suggestion is borne in on one that a small difference in the presence or 

 the potency of a single enzymatic determiner may change the intensity 

 of the color enough to throw the flower into a different phenotype. It is 

 very possible that environmental conditions affecting the physiological 

 condition of the plant may throw plants of the same genotypic constitu- 

 tion into different phenotypes. 



The behavior of pedigree 132 (table 5) appears to indicate that the 

 light blues considered here were heterozygous as to the genes R, B, and X. 

 The expected types all appeared except mauve and tinged white, and 

 considering the small number of individuals it is not surprising that 

 these two types also were not represented. No other types appeared. 



Also, in the pedigree from plant 222-10 (a plant recorded as light blue), 

 there occur the types dark blue, light blue, mauve, tinged w^hite, and white, 

 all of which may come from a plant of the constitution CCRrBbXx. 

 The Fi plants in this pedigree consisted of this plant and 4 other light 

 blues. When selfed, the others also threw dark blues, light blues, mauves, 

 tinged whites, and whites. 



Type 7 Dark blue ' (Plate I) 



Description of the type. — The type called dark blue is a brilliant, almost 

 electric blue. This type is explained as due to the presence of a gene B 

 in either simplex or duplex condition, in addition to aU the genes necessary 

 for the mauve type. 



Theoretical consideration of data. — The dark blue plants that were 

 selfed fell into two classes, those that bred true and those that threw 

 other types. 



In the first group there were 17 plants, of which 9 were Fi hybrids 

 and threw 35 dark blues, and 8 were not hybrids and gave 38 dark blues. 



Altho the number in any of these pedigrees is small individually and 

 cannot be taken as conclusive that these plants were homozygous in all 

 the genes that go to make the dark blue type, the evidence is strong 

 that such was the case. Such plants, then, may be considered to be 

 duplex for all the genes (CCRRBBXX). 



Other dark blues when selfed broke up into dark blues, light blues, 

 mauves, and pinks (and in one case a doubtful light purple). The data 

 are from only 8 Fi plants, and the total F2 progeny numbers only 72. 

 Their behavior, however, shows that these dark blues must have been 

 simplex for the gene B, so that, when selfed, it could drop out from some 

 of the recombinations giving rise to the mauves and the pinks. 



135 



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