66 NILS HERIBERT-NILSSON 



tween the gametes, or a kind of selfsterility in the genes not yet under- 

 stood. Instead all the R-eggs are fertilized by r-pollen, which is 

 always in excess in ordinary cases. Thus the combinations 2 Rr, rR, 

 and rr are obtained, that is 3:1 segregation. Therefore, we cannot 

 assume a formation of the combination RR and its subsequent dege- 

 neration in the zygote or in the early seed stage as is known to occur 

 in cases of elimination, but the combination RR cannot become rea- 

 lized. I call this process prohibition. The term substitution here 

 adopted applies to the compensation of the /?-pollen with r-pollen in 

 the fertilization of the R-eggs. The abnormal segregation of selffertili- 

 zed red nerved pants is brought about by the cooperation of the compli- 

 cations just mentioned resulting in a displacement of the expected 2 : 1 

 segregation up to 6 : 1 in extreme cases. 



The great disturbances in the segregation in 0. Lamarckiana is 

 due to the long style. The longer the style the greater the differences 

 in the gamete representation in spite of the fact that the relative 

 difference in the rate of growth of the pollen tubes is the same. 



The segregation in 0. Lamarckiana is in general abnormal, or 

 obscure, or changeable. This has been the rule in the mutation crosses 

 of DE Vries. The irregular segregation stated by de Vries can be 

 fully explained by the complications characteristic of the factor R, 

 as I have showed in detail by examples taken from his own experi- 

 ments. From the fact that segregation took place already in the first 

 generation and, further, because of the changeable and non-typical 

 segregative numbers de Vries concluded that mendelian segregation 

 did not take place in Oenothera. The process of prohibition explains 

 the peculiarity first mentioned, while the other peculiarity is made 

 intelligible by the act of certation. There is every probability that 

 the opinion expressed by de Vries and, further, by Gates, Shull, and 

 Bartlett that the segregation in Oenothera Lamarckiana is a pheno- 

 menon sui generis loses its authority the more the plant is investigated. 

 In fact, there seem to be no real grounds any longer for the main- 

 tenance of such an opinion. 



ZITIERTE LITERATUR. 



CoRRENS, C. 1902. Scheinbare Ausnahmen von der Mendelschen Spaltungsregel 

 für Bastarde. — Ber. d. Deutsch. Botan. Gesellsch. 20, S. 159. 



— 1917. Ein Fall experimenteller Verschiebung des Geschlechtsverhältnisses. 

 — Sitzungsber. d. Königl. Preuss. .A,kad. d. VVissensch. 1917, Nr. 51, S. 685. 



