Phenomena of Inheritance 103 



from which our cultivated sweet peas are descended." This is 

 apparently a typical case of reversion and its cause was found in 

 the fact that at least two factors are necessary in this case for 

 the production of color, a pigment factor R and a color devel- 

 oper C. One of these was lacking in each of the white parents, 

 their gametic formulae being Cr and cR respectively, but when 

 these two factors came together in the offspring a purple-flowered 

 type was produced with the zygotic formula CcRr. These F l 

 plants produced colored and white F 2 plants in the proportion of 9 

 colored to 7 white and the colored forms were of six different 

 kinds (Fig. 33). For the production of these six colored forms 

 five different factors must be present in the gametes, according 

 to Punnett, viz.: (i) a color base R, (2) a color developer C, 

 (3) a purple factor P, (4) a light wing factor L, (5) a factor for 

 intense color /. When all of these factors are present the result 

 is the purple wild form with blue wings, while the omission of 

 one or more of these factors leads to the production of six 

 forms of colored and various types of white-flowered plants of 

 the F 2 generation. 



Castle found that eight different factors may be involved in 

 producing the coat colors of rabbits : these are : 



C a common color factor necessary to produce any color. 



B a factor acting on C to produce black. 



Br a factor acting on C to produce brown. 



Y a factor acting on C to produce yellow. 



I a factor which determines intensity of color. 



U a factor which determines uniformity of color. 



A a factor for agouti, or wild gray pattern, in which the tip of 

 every hair is black, its middle yellow, its basal part gray. 



E a factor for the extension of black or brown but not of 

 yellow. 



Plate found that all of these factors except the last, E, are also 

 involved in the production of the coat colors of mice. Baur has 

 recognized more than twenty different factors for the color and 

 form of flowers in the snapdragon, Antirrhinum. 



