66 APPLICATION OF PEINCIPLES OF HEREDITY TO BREEDING. 



red color. When the thn*d is present with the first two purple arises. 

 There are other cryptomeres present in gillyflowers which modify 

 these colors, but the numerical relations in their transmission have 

 not yet been fully made out. 



Shull found a cryptomeric character in beans in a cross between 

 certain brownish-seeded beans and white-seeded beans. It appears 

 that the white variety carried a cryptomere which when present with 

 the factor which gives rise to the brown color converts the brown 

 into black, thus giving in the hybrid a character which was apparently 

 absent in both of its parents. 



In this case we may represent the formula of the two parents as 

 follows: 



White parent = BBpp. 

 Brown parent = hhPP. 



Here B stands for the cryptomere w^hich converts the brown 

 color into black (and which is latent in the absence of P) and P for 

 the producer of the brown pigment. The hybrid would have the 

 formula BhPp, The second generation of this hybrid would be as 

 follows : 



B. P. pb. 



1 BBPP 1 



2 BBPp 2 



1 BBpp 1 



2 BhPP 2 

 4 BhPp 4 



2 Bbpp 2 



B. P. pb. 



1 bbPP 1 



2 bbPp 2 



1 bbpp 1 



16 



The first column in the above table gives the nine types in the sec- 

 ond generation of the hybrid , and the figures at the left of the formula 

 show the relative frequency of the types. Thus type BBPP consti- 

 tutes one-sixteenth of the second generation, type BBPp two-six- 

 teenths, and so on. Since B and P are both present in types BBPP, 

 BBPp, BhPP, and BhPp, these four types, constituting together 

 nine-sixteenths of the second generation, will all be black. Types 

 hhPP and hhPp are brown, while types BBpp, Bhpp, and hhpp 

 will all be white, although two of them have the factor B. The 

 factor B has no effect in the absence of P. We thus have in the 

 second generation of this hybrid 9 blacks, to 3 browns, to 4 whites. 



A more complex case of this kind is that of the purple gillyflowers 

 already mentioned. In this case we have to deal with the following 

 factors : 



C=one factor of red. 

 P=other factor of red. 

 P=the factor for purple. 



Of these factors C and R are cryptomeric to each other; that is, 

 neither of them produces a visible effect except in the presence of 

 the other. P is cryptomeric to both C and R. The factor P was 



