ANTHOCYANINS AND GENETICS 173 



It was found that members of (.4) might throw (B) but not vice 

 versa. 



Shull (513) gives an account of the results obtained by crossing 

 several varieties, i.e. 



'Prolific black wax' purple-black seeds (anthocyanin in testa). 



'Ne plus ultra' yellow-brown seeds. 



'Long yellow six- weeks' light greenish-yellow seeds. 



'White flageolet' seed coats white. 



The results in Fj were as follows: 



Purple x yellow-brown = purple. 

 Purple x yellow purple. 

 White x purple 



All gave similar F, with testa mottled 

 White x yellow-brown \ ., 



with purple. 

 White x yellow ) 



Shull then postulates the following factors: 



P = pigment. 



B = modifier which changes pigment to purple. 



M = mottling factor. 



Then the constitution of the different beans is 

 Brown and yellow Pbm. 

 Black beans PBm. 

 White pBM. 



Shull concludes that the mottling factor is carried by the white 

 bean, whereas Bateson and Tschermak had regarded the mottling factor 

 as latent in the pigmented bean. 



Shull in a later paper (521) gives the proportions of the varieties 

 in F 2 from the above cross. They were found to be 



Purple mottled 18. 

 Purple self-colour 18. 

 Brown or yellow mottled 6. 

 Brown or yellow self-colour 6. 

 White 16. 



Shull's explanation for this result is that beans containing PB and 

 heterozygous in the M factor are mottled, whereas those beans 

 homozygous in M are self-coloured. Hence it is possible for purple to 

 carry the mottling factor, and Tschermak, Bateson and Lock are also 

 correct. Mottled beans of the above constitution are heterozygous 

 and should never breed true, and this was found to be the case. Shull 



