n6 PROBLEMS OF GENETICS 



Note. 



Since this chapter was written two contributions of special 

 importance have been made to the study of the Oenothera prob- 

 lems. The first is that of Heribert-Nilsson. 9 The author begins 

 by giving a critical account of the evidence for de Vries's inter- 

 pretation of the nature of the mutants. In general this criticism 

 pursues lines similar to those sketched in the foregoing chapter, 

 concluding, as I have done, that the chief reason why factorial 

 analysis has been declared to be inapplicable to the Oenothera 

 mutants is because no one has hitherto set about this analysis 

 in the right way. He has also himself made a valuable beginning 

 of such an analysis and gives good evidential reasons for the belief 

 that at least the red veining depends on a definite factor which 

 also influences the size of certain parts of the plant. He argues 

 further that many of the distinctions between the mutants are 

 quantitative in nature. With great plausibility he suggests that 

 the system of cumulative factors which Nilsson-Ehle discovered 

 in the case of wheat (subsequently traced by East in regard to 

 maize) may be operating also in these Oenotheras. According 

 to this system several factors having similar powers may coexist 

 in the same individual, and together produce a cumulative effect. 

 Scope would thus be given for the production of the curious and 

 seemingly irregular numbers so often recorded in the "mutating" 

 families. 



Another remarkable observation relating to the crosses of 

 muricata and biennis has been published by Goldschmidt. 10 

 He finds that in the formation of this cross the female pronucleus 

 takes no part in the development of the zygotic cell, but that 

 when the male pronucleus enters, the female pronucleus is 

 pushed aside and degenerates. As de Vries observed, the recip- 

 rocal hybrids are in each case very like the father ("stark 

 patroklin") , a consequence which finds a natural explanation in 

 the phenomenon witnessed by Goldschmidt. The results of 

 the subsequent matings can also be readily interpreted on the 

 same lines. Indications of maternal characters are nevertheless 



9 Zts. f. Abstamm., 1912, VIII. 



10 Arch. f. Zellforschung, 1912, IX, p. 331. 



