THEORY OF REVERSION 227 



The relation between the constituent factors and 

 the resulting external appearance can be more readily 

 perceived by comparing the Table on p. 229 with 

 that on p. 228. 



The factor for fink is written O 

 The factor for absence of fink d 

 The factor for blue • 

 The factor for absence of blue C 



In this Table, as in that representing gametic 

 unions in seed-coat colour, the four whites occupy 

 the four bottom right-hand squares. The three whites 

 in the squares 11, 12 and 15 carry the factor for blue, 

 as the Table on p. 229 shows. There are two types 

 of them. One of them, No. 11, is homozygous for the 

 blue factor ; the other two, Nos. 12 and 15, are hetero- 

 zygous for the blue factor. The only white carrying 

 no blue is the one in square 16. That is to say, 

 there are three zygotic types oi whites altogether. 



Now, it must not be supposed that the corre- 

 spondence between the theory, as set forth on this 

 Table, with the actual result which it was invented 

 to explain, is proof that the theory is true. It cannot 

 be denied that the expectation based on this theory 

 is the occurrence of four white, three pink, and nine 

 purple -flowered plants amongst every sixteen, on the 

 average, in the second hybrid generation. Nor can it 

 be denied that these three things occur in these propor- 

 tions. But a great deal more than this is wanted before 

 the truth of the theory can be admitted. The three 

 zygotic types of white, for instance, must be shown 



