OUTSTANDING BIOLOGICAL ADVANCES 39 



results similar to those obtained with the first filial 

 generation. 



This great principle of alternative inheritance was 

 exhibited throughout the extensive 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: " When- 

 ever there occurs a pair of differentiating characters, 

 of which one is dominant to the other, three possibil- 

 ities exist: there are recessives which always breed 

 true to the recessive character; there are dominants 

 which breed true to the dominant character, and are 

 therefore pure; and, thirdly, there are dominants 

 which may be called impure, and which on self- 

 fertilization (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 con- 

 sequence 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 



