Heredity Studies in the Morning-Glory 25 



Mauve crossed with dark purple. — Cross 107 gave 3 dark purples in Fi, 

 Avhich gave dark purples, dark blues (a type often intergrading with the 

 lighter purples), and magentas in Fo. In eross 153 the Fi plant was 

 recorded and checked as "light blue," but it did not behave as a light 

 blue should. It acted, when selfed, as a light purple might, and threw 

 dark purples, dark blues, and magentas. It must, then, have borne the 

 intensifying genes X and I at least in simplex condition, as in the following 

 schema : 



Fi 

 CCRRbbXxii mauve 



X CCRRBb^ 



CCRRBBXXII dark purple 



XX li dark purple 

 Xxli light purple 



Type 5 Magenta (Plate I) 



Magenta crossed with light blue. — Four crosses are recorded in this class 

 and they all gave light purples in Fi. Such crosses should give rise to 

 plants heterozygous for the genes B, X, and I, a condition which would 

 cause the flowers to be light purple. A fifth cross, 197, produced two 

 plants, both of which were recorded as "dark purple." 



The fact that these light purple plants threw tinged whites and whites 

 in F2 indicates that the light blue parent was simplex for R also, and, 

 in the case of cross 197, for X as well, as has since been further indicated 

 by other progenies from it grown by J. J. Pollock and the writer. 



Magenta crossed with dark blue. — Three crosses in this class, 188, 190, 

 and 192, gave dark purple and light purple Fi plants. Two other crosses, 

 189 and 191, remain to be explained as apparently exceptional cases. 



If magenta is crossed with dark blue the Fi plants will be simplex for I, 

 which, reacting with B from the blue parent, will result in purple, as in 

 the above cases. 



Cross 189 gave 3 plants recorded as " magentas," besides 2 dark purples, 

 in Fi. Further data, however, give indication that these "magentas" 

 were really light purples which had been recorded after their colors had 

 begun to break down prior to the flowers' withering. 



Cross 191 gave i dark purple and i light purple. White appeared 

 in F2, indicating that the Fi plant from which it came was simplex for R. 

 Since dark blue and magenta are both duplex for R, according to hypo- 

 thesis, an explanation must be sought for the appearance of the white 

 in F2. The original blue parent was recorded in the greenhouse as light 

 blue, then checked once as dark blue. The behavior of the cross would 

 indicate that it was really a light blue, which, by hypothesis, can be 

 simplex for R. 



141 



