356 Oriffin and Behaviour of Oenothera rubricalyx 



to lead to conclusions which he docs not wish to accept. But if the 

 Mendelian argument holds in nthcr cases (as I think it docs), then it 

 will have to be admitted to hold also in this case. The significance of 

 mathematical ratios can no more be suspended for the convenience 

 of some one, than can the law of gi-avitation. I hold no brief for 

 Mendelism, but when the fiicts point so clearly to a 3 : I ratio in 

 the offspring of the rubricalyx mutant, and a 1 : 1 in the cross of a 

 heterozygous rubricalyx individual with another species, I am not loath 

 to draw the inevitable conclusion that the mutation originated through 

 a single dominant unit-change antl that heterozygous plants were pro- 

 ducing two types of germ cells in equal numbers. 



The evidence is as follows : The offspring of the original rubricalyx 

 mutant which were not accidentally destroyed numbered only 12. Of 

 these, 10 came into bloom, and 9 of them were shown by their buds to be 

 rubricalyx and 1 ruhrinervis. Two other plants remained losettes, and 

 I formerly classed them as undetermined or doubtful because they 

 showed only a small amount of "ventral" red. Subsequent examination 

 of many rosettes, however, has shown that whenever there is even a 

 trace of ventral red on the rosettes the plants invariably develop red 

 buds. Hence all rosettes which were formerly classed as doubtful 

 because they showed only small amounts of ventral red, were really 

 rubricalyx. The above ratio in the F^ of the 7-vhricalyx mutant was 

 therefore 11 rubricalyx : 1 rubrinervis. This number is of course too 

 small to determine a ratio. But three of the rubricalyx plants in this 

 culture were selfed and yielded F.^ families containing rubricalyx and 

 rubrinervis in the ratios respectively of 10 : 5, 14 : (5 and .33 : 11. These 

 three ratios are all very closely in accord with 3:1, and even the 11:1 

 ratio is not a wide departure. Adding these four ratios we have a 

 total ratio of 68 : 28, which is extremely close to a 3 : 1 ratio, while the 

 chances against it representing a 15 : 1 are enormous. 



This evidence in itself is clearer and more indubitable than that 

 on which many conclusions from Mendelian ratios rest. But there is 

 still more evidence, which Shull omits to quote. Two of the rubricalyx 

 plants in the F^ culture which gave the ratio 33 : 11 and thereby 

 proved the monohybrid character of rubricalyx, were crossed reci- 

 procally with Oe. (jrandiflora. They both proved to be heterozygous 

 in regard to a single character-difference, for in both cases the F^ 

 contained about 50 % red-budded and 50 % green-budded plants. Thus 

 in rubricalyx x grandijlora, of 67 plants 58 came into bloom, and of 

 the latter 30 were red-budded and 28 green-budded. This is a far 



