Heredity Studies in the Morning-Glory 7 



The classification into types is in many cases rather arbitrary. The 

 pinks verge into pale mauve, and dark mauves are about the same as 

 lighter magentas. In the same way, dark blue is very like some of the 

 hybrid light purples, while other hybrids of this type are hardly less 

 intense in color than typical homozygous dark purples. 



HEREDITY OF COLOR OF SEED COAT 



The seed coats of the morning-glory plants studied were of two colors — 

 black and a light yellowish brown, or tan. These two colors were found 

 to be inherited in an alternative and exclusive manner as a simple men- 

 delian allelomorphic pair of characters. Black was dominant over tan. 



Since the integuments of a seed are part of the maternal (Pi) somatic 

 tissues, seeds borne on plants that are either duplex or simplex for black 

 will in either case be black-coated. Only a pure recessive plant can bear 

 tan-coated seeds. However, a tan-coated seed can contain a simplex 

 embryo, resulting from the fecundation of the recessive ovule by a dom- 

 inant germ. A black-coated seed can contain a duplex or a simplex domi- 

 nant embryo, or even a double recessive embryo. The embryo always 

 represents, of course, a different generation from the seed coat that 

 contains it. 



TABLE I. Data of Color of Seed Coats in Hybrid Pedigrees of Pure 



Recessives* 



* The dominant character black is symbolized by B, the recessive tan by b. 



t The seed parent in cross ii8 bore black-coated seeds and several of the Fi sibs to no. 5 were black- 

 coated. No. 1 1 8-5 itself, however, was a pure extracted recessive. 



The color of seed coats in hybrid pedigrees of pure recessives is shown 

 in table i. The following system was used for numbering the plants: 

 Each progenitor of a pedigree was given a number below loo; crosses 

 were designated by numbers m the hundreds, a different set of hundreds 

 being used for each year. Individual offspring from a self-fertilized plant 

 were designated by consecutive numbers separated from the number of 



1-^3 



