LATENT CHARACTERS 211 



Painted Lady is a well-known colour type which is 

 characterized by the presence of a red standard and 

 white wings. Picotee and tinged white are also forms 

 well known to the sweet-pea fancy. They appear to 

 be diluted forms of the purple and Painted Lady types 

 respectively, their appearance depending upon the 

 presence of a definite diluting factor in addition to the 

 factor for the colour in question, or perhaps more 

 properly upon the absence of the proper strengthening 

 factor which converts Picotee into purple, and tinged 

 white into Painted Lady. 



The following explanation of the result so far 

 described has now been well established by further 

 experiment. In the first place, we may consider all the 

 coloured forms together as a single group opposed to 

 white. It is now clear that the coloured type of F x is 

 due to the meeting together of two factors, one of them 

 borne by one white parent and the other by the second 

 and it is necessary for both these factors to be simul- 

 taneously present in order that any colour may make 

 its appearance. We may call these two factors C and 

 R, denoting the absence of either by c and r respectively. 

 By the simple Mendelian behaviour of these two pairs 

 of factors C-c and R-r, the ratio of nine coloured 

 plants to seven white appearing in F 2 is readily 

 explicable, and the way in which this happens is shown 

 in the diagram (Fig. 16). 



To explain the presence of the four different types of 

 coloured plants which make their appearance in F 2 , 

 two further pairs of allelomorphs are called in. The 



dominant member (B) of one of these, when present 



142 



