THE MUTATED GENE 63 



nana gives off less auxin from the tip of the coleptile and also 

 that it grows less with the same amount of auxin. It was found 

 that the reason for both is that in nana auxin is destroyed at a 

 higher rate. The reason for this seems to be a change in oxida- 

 tion reduction. In this case, the result is only dwarfism, but a 

 similar effect might in other cases lead to tissue destruction, as 

 in the vestigial wing. 



There is one case existing in plants that falls in line with the 

 facts discussed in this and the foregoing chapter and has been 

 used also to derive a corresponding explanation. Oehlkers 

 (1930-1935) analyzed the Cruciata character of Oenothera. 

 This hereditary pathological trait might be compared to cases of 

 Homoeosis in Drosophila, as homologous organs replace each 

 other. Cruciata flowers are sepaloid, the petals being more or 

 less transformed into sepals. All transitions exist from petals 

 with a trace of sepaloidy through different mixtures of petal and 

 sepal tissue to pure sepals. The trait (which had already been 

 studied by de Vries and others) behaves as a simple Mendelian 

 recessive. The grade of sepaloidy is also inherited, is typical 

 for each Oenothera complex, and remains constant in crosses. 

 The phenotypic effect of different combinations follows simple 

 quantitative rules and is such as expected, if each of these 

 Cruciata genes — assuming them to be members of an allelo- 

 morphic series — has a definite quantitative effect in regard to the 

 Cruciata character. The case therefore resembles most closely 

 the case of the sex genes in Lymantria, where also a series of 

 different conditions of the gene exist, which in all combinations 

 have the proper additive effect which can be calculated from the 

 individual effects. Oehlkers represents his facts, then, using the 

 type of the diagram introduced for Lymantria and in terms of 

 assumed quantities of action of the respective genes. His 

 diagrammatic representation of the facts takes as a basis a 

 quantity of 10 for one definite complex with complete sepaloidy 

 and of 42 for one with complete normality. Parallel to the case 

 of intersexuality in Lymantria, it is assumed that everything 

 above 26 is normal, below 16 sepaloid, and between 16 and 26 

 intermediate in five classes (Fig. 22). The different combinations 

 of complexes with Cruciata must then give consistent results if 

 definite quantities are assigned to the individual actions. This 

 is the case. 



