Ill MENDEL'S WORK 23 



9 coloured tails, 3 white tails, 3 coloured dwarfs, 

 and I 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 indi- 

 viduals 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^ generation 

 produced by such hybrids consists on the average 

 of 9 showing both dominants, 3 showing one 

 dominant and one recessive, 3 showing the other 

 dominant and the other recessive, and i showing both 

 recessive characters. And, as Mendel pointed out, 

 the principle may be extended indefinitely. If, for 

 example, the parents differ in three pair of characters 

 A, B, and C respectively dominant to a, b, and c, the 

 Fj individuals will be all of the form ABC, while 

 the Fg generation will consist of 27 ABC, 9 ABc, 

 9 AbC, 9 aBC, 3 Abe, 3 aBc, 3 abC, and i abc. 

 When individuals differing in a number of alternative 

 characters are crossed together, the hybrid generation, 

 provided that the original parents were of pure 

 strains, consists of plants of the same form ; but 

 when these are bred from, a redistribution of the 

 various characters occurs. Tnat redistribution follows 

 the same definite rule for each character, and if the 

 constitution of the original parents be known, the 

 nature of the F^ generation, i.e. the number of 

 possible forms and the proportions in which they 



