OENOTHERA RUBRINERV1S, A HALF MUTANT. 371 



analogous way. The main difference, as I have pointed out in Grup- 

 penweise Artbildung, it that some types of hybrids, as we might 

 expect, are constantly absent or suppressed, as I called it. If we 

 assume this suppression to take place in the pollen before fecunda- 

 tion, the remaining phenomena are easily explained on this basis. 

 It will be sufficient to review the facts given in my book, and to 

 combine them with the results of some determinations of the amount 

 of barren grains in the seeds of self fertilized and crossed individuals. 



The amount of empty seeds is about the same in 0. oblonga as 

 in 0. Lamarckiana. For the cultures of 1911, mentioned in my book, 

 I found among the seeds of two self-fertilized individuals 25 and 

 33 per cent of germs. Seeds of biennial plants collected in 1913 con- 

 tained 30—18 and 17 per cent of germs; but seeds of annual plants, 

 saved in 1914 on two new mutants from 0. Lamarckiana and one 

 from 0. cana, gave only 6—5 and 6 per cent of germs. Annual spe- 

 cimens are always much weaker than biennial ones, and their fruits 

 are often thin instead of club-shaped. These figures evidently point 

 to a complete analogy with 0. Lamarckiana. 



The question whether the lethal factors are the same as in 0. 

 Lamarckiana may be answered by crosses with this species. I tried 

 the seeds of a cross 0. oblonga x Lamarckiana, of one of 0. oblongax 

 nanella, both made in 1911, and of a cross of 1913 of 0. oblongax 

 0. cana. I found 53—40 and 34 per cent of good germs. The figures 

 do not essentially differ from those found for self-fertilized Lamarcki- 

 ana, and thereby show that the lethal factors must be the same 

 and simply inherited by 0. oblonga from its parent species without 

 change. 



The ovules which produce empty grains after self fertilization 

 may develop into normal seeds after crosses with other species, even 

 as in the case of 0. Lamarckiana itself. 0. oblongax biennis gave 92 

 per cent of germs, 0. oblongax atrovir ens (cruciata) 87 per cent, 0. 

 oblongax Hooker i 90 per cent, and 0. syrticola (muricata)x oblonga 

 90 per cent. Thus we see that in this respect also the lethal factors 

 are the same as in 0. Lamarckiana. 



Our assumption is that 0. oblonga arises by means of a mutation 

 in the Lamarckiana gametes of our species, leaving the velutina 

 gametes unchanged. The formula for self-fertilization, assuming 

 the oblonga gametes to be suppressed in the pollen before fecunda- 

 tion, is as follows: (obl.+velu.)xvelu.=obl.xvelu.+veluxvelu. 

 This explains the constancy of the mutant, since the velutinax 

 velutina germs contain the same lethal factor on both sides and thus 



