HEREDITY AND GERMINAL CONTINUITY 317 



color was not blotted out was clearly demonstrated by allow- 

 ing the hybrid generation to develop by self-fertilization. 

 Under these circumstances a most interesting result was at- 

 tained. The filial generation, derived by self-fertilization 

 among the hybrids, produced plants with yellow and green 

 seeds, but in the ratio of three of the yellow to one of the 

 green. All of the green-seeded individuals and one- third of 

 the yellow proved to breed true, while the remaining two- 

 thirds of yellow-seeded plants, when self -fertilized, produced 

 yellow and green seeds in the ratio of three to one. Subse- 

 quent breedings gave an unending series of results similar 

 to those of the first filial generation. This great principle 

 of alternative inheritance was exhibited throughout the ex- 

 tensive experiments of Mendel, and it is now recognized 

 as one of the great biological discoveries of the nineteenth 

 century. Mr. R. C. Punnett gives (1905) a remarkably clear 

 and terse statement of the facts as follows: " Whenever there 

 occurs a pair of differentiating characters, of which one is 

 dominant to the other, three possibilities exist: there are 

 recessives which always breed true to the recessive character; 

 there are dominants which breed true to the dominant char- 

 acter, and are therefore pure; and thirdly, there are domi- 

 nants which may be called impure, and which on self-fertiliza- 

 tion (or in breeding, where the sexes are separate) give both 

 dominant and recessive forms in the fixed proportion of three 

 of the former to one of the latter." 



The results of Mendel's experiments are the consequence 

 of the fact that the germ-cells retain their purity with respect 

 to unit characters. That is, in the combination of germ-cells 

 by cross-breeding, the hereditary qualities do not lose their 

 individuality — they are mixed but not blended. When the 

 germinal elements are formed in these hybrid plants two 

 classes of germ-cells will arise in equal number, one class 

 carrying the dominant, and the other the recessive quality. 



