in MENDEL'S WORK 25 



bearing white flowers the resulting hybrid was a tall 

 plant with coloured flowers. For coloured flowers are 

 dominant to white, and tallness is dominant to dwarf- 

 ness. In the succeeding generation there are plants with 

 coloured flowers and plants with white flowers in the pro- 

 portion of 3:1, and at the same time tall plants and 

 dwarf plants in the same proportion. Hence the chances 

 that a tall plant will have coloured flowers are three 

 times as great as its chance of having white flowers. 

 And this is also true for the dwarf plants. As the result 

 of this cross, therefore, we should expect an F 2 genera- 

 tion consisting of four classes, viz. coloured tails, white 

 tails, coloured dwarfs, and white dwarfs, and we should 

 further expect these four forms to appear in the ratio of 

 9 coloured tails, 3 white tails, 3 coloured dwarfs, and 1 

 white dwarf. For this is the only ratio which satisfies 

 the conditions that the tails should be to the dwarfs as 

 3:1, and at the same time the coloured should be to 

 the whites as 3 : 1 . And these are the proportions that 

 Mendel found to obtain actually in his experiments. 

 Put in a more general form, it may be stated that when 

 two individuals are crossed which differ in two pairs of 

 differentiating characters the hybrids (Fj) are all of the 

 same form, exhibiting the dominant character of each 

 of the two pairs, while the F 2 generation produced by 

 such hybrids consists on the average of 9 showing both 

 dominants, 3 showing one dominant and one recessive, 



