ON THE NATURE AND BASIS OF HEREDITY. 181 



When a tall variety was crossed with a short one, the result was that all of the 

 offspring were tall; hence the character "tall" was called dominant; "short" was 

 called recessive. The same result was reached with the other characters. When the 

 hybrids were bred together both characters reappeared, and always in definite 

 proportions: (A) 3 dominants to 1 recessive. (J5) 1 dominant : 2 hybrids : 1 recessive. 



The fact that the same ratio appeared in each one of the seven sets of experi- 

 ments seemed to demonstrate several important points: (1) that there was some 

 uniform law governing the results ; (2) that specific characters stood for definite 

 units — -"purity of germs," as Professor Bateson calls it; (3) there were no transi- 

 tional phases, no passing of one character gradually into another. 



When thus presented, the facts tell strongly against the origin of species by 

 gradual modification as held by Darwin, and strongly support the contention of 

 de ^'ries for mutation as the mode of evolution. No wonder that the work was 

 hailed with such delight by de Vries and Bateson. 



On looking at the two classes of characters — ^the dominants and recessives — it 

 becomes obvious that the results would not bear out the conclusions. For example, 

 is it not clear that there can be no such impassable hmit between "tall" and "short" 

 as claimed? Whatever the ratio discovered means, it can not mean anj- absolute 

 impasse between two such characters. In no case of these contrasting characters does 

 it seem at all probable that there can be no transitional or intermediate conditions. 



A simple question as to these pairs of dominants and recessives was this: Could 

 one on hearing the names of the pairs predict which one in each pair would be 

 dominant and which recessive? I took the list given by Mendel, and, before 

 informing mj-self of Mendel's results, underhned the characters which I conject- 

 ured would be likely to be dominant. The guess turned out correct in every one 

 of the seven cases. 



The meaning of dominance and recessiveness is, then, only greater or less vigor, 

 greater or less stabilitij. In the case of "tall" and "short" it is vigor, in the case of 

 axillary or terminal flowers it is preponderance of stabilitj^ — ^the older character 

 being the more firmly fixed. This is enough perhaps to be suggestive. 



Now, we find differences in vigor and in the stabiUty of characters ever3'^vhe^e, 

 but we do not alwaj-s get the Mendelian ratios. The ratios we get, if we get any at 

 all, are quite different in different species, and that might have been foreseen. 

 [Here the lecturer continued the subject without manuscript, and but few addi- 

 tional pages (see two paragraphs in advance) were ever written;* the outline from 

 which he spoke is of interest, however, and is as follows. — Editor.] 



Mention — 



(a) Results in crossing: Japanese turtle and blond ring-dove; Japanese turtle and white ring; 

 Japanese turtle and homer; Japanese turtle and common pigeon; Hybrid and homer; White ring and 

 humilis. First generation — dark cJ and white 9 . European turtle and ring — o^ dark and light ? . 

 Japanese turtle and ring — d dark and light 9. This seems' to be a general law with pigeons, 

 but I should not dare to say it holds as a universal law. 



{b) Sex-alteration." (Z 5) 



INIendel' did not undertake to develop a theory of evolution, his aim being to 

 discover the principles that govern hybridization. His experiment with peas, as he 



* The firat part of Chapter I has a short statement on Mendelian heredity. — Editor. 



' That is, "dark male and light female" hybrids. — Editor. 



^ Written December 1907 (before, or at the same time with, the immediately preceding pages). — Editor. 



