ON THE NATURE AND HASIS <>! I! I.KKIHTV. 181 



When a tall variety was crossed with a short one, the result w;is tli.-it nil of tin- 

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

 called recessive. The same result was reached with the other characters. \Yhen t he 

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

 proportions: (A) 3 dominants to 1 recessive, (B) 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 \vere 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 Vries for mutation as the mode of evolution. No wonder that the Avork 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 Avould not bear out the conclusions. For example, 

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

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

 impasse betAveen tAvo such characters. In no case of these contrasting charad ers 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: ( 'ould 

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

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

 informing myself of Mendel's results, underlined the characters Avhich I conject- 

 ured Avould 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 nY/or, 

 greater or less stability. In the case of "tall" and "short" it is A r igor, in (ho case of 

 axillary or terminal floAvers it is preponderance of stability the older character 

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



NOAV, we find differences in vigor and in the stability of characters everywhere, 

 but we do not always get the Mendelian ratios. The ratios AAT get, if we get any at 

 all, are quite different in different species, and that might haA'e been foreseen. 

 [Here the lecturer continued the subject Avithout manuscript, and but few addi- 

 tional pages (see two paragraphs in advance) Avere ever Avritten; 4 the outline from 

 Avhich he spoke is of interest, however, and is as follows. EDITOR.] 



Mention 



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

 Japanese turtle and homer; Japanese turtle and common pigeon; Hybrid and homer: "\Yhito ring and 

 humilis. First generation dark c? and white 9 . European turtle and ring o 1 dark and %! 

 Japanese turtle and ring cT dark and light ?. This seems 6 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) 



Mendel 6 did not undertake to develop a theory of evolution, his aim being to 

 discover the principles that govern hybridization. His experiment Avith pens, ns he 



4 The first part of Chapter I has a short statement on Mendelian heredity. EDITOR. 



5 That is, "dark male and light female" hybrids. EDITOH. 



6 Written December 1907 (before, or at the same time with, the immediately preceding pages). EDITOR. 



