52 A MANUAL OF MENDELISM 



Albinism, or, at any rate, whiteness, producible by 

 either of two separate factors was revealed in Professors 

 Bateson's and Punnett's experiments with sweet-peas, 

 the details of which are found in the " Reports to the 

 Evolution Committee." Two plants were found with 

 colourless flowers which bred true, but, when crossed 

 with each other, threw coloured hybrids. The coloured 

 hybrids, by being different from both parents, are 

 evidence of two pairs of characters at least and four 

 groups of hybrids' progeny, as follows : 



9 ; 3 : 3:1 



If the hypothesis of two pairs of characters be correct, 

 it will be observed that, when the dominants carried by 

 the two middle groups are brought together, the flower 

 which carries them is coloured. From this it is a fair 

 inference that the colourlessness of the two parents and 

 therefore of the two middle groups is due to the reces- 

 sives they carry. And, since it carries both these 

 recessives, it is to be inferred again that the fourth 

 group should also be colourless. Thus, in the hybrids' 

 progeny there should be only one coloured group and 

 three colourless, and the numbers in the coloured group 

 should be to those in the three colourless groups together 

 in the ratio 9 : 7, i.e. 9 : (3 : 3 : 1). When the hybrids' 

 progeny were counted, they were found to consist of 

 2132 plants with coloured flowers and 1593 with colour- 

 less. If these figures be divided by 232'81, the figure 



