igig] DeVRIES— OENOTHERA RUBRINERVIS 21 



plants, saved in 1914 on two new mutants from O. Lamarckiana 

 and on one from O. cana, gave only 6-5 and 6 per cent of germs. 

 Annual specimens 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 O. Lamarckiana. 



The question whether the lethal factors are the same as in 

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

 tried the seeds of a cross O. oblonga X Lamarckiana , of one of O. 

 oblongaXnanella, both made in 191 1, and of a cross of 1913 of 

 O. oblonga XO. cana. I found 53-40 and 34 per cent of good germs. 

 The figures do not essentially differ from those found for self- 

 fertilized Lamarckiana, and thereby show that the lethal factors 

 must be the same and simply inherited by O. 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 O. Lamarckiana itself. O. oUongaXbiennis gave 

 92 per cent of germs, O. oblongaXatrovirens (cruciaia) 87 per cent, 

 O. oblongaXHookeri 90 per cent, and O. syrlicola {muricata)X 

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

 lethal factors are the same as in O. Lamarckiana. 



Our assumption is that O. 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.-fvelu.) Xvelu. =obl. Xvelu.+velu.Xvelu. 

 This explains the constancy of the mutant, since the velutinaX 

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

 produce the empty grains. If we compare this formula with the 

 results of the crosses described in my book (pp. 266-267), we find 

 a complete harmony, as I shall now try to show. 



Fertilized by O. Lamarckiana and analogous mutants, O. oblonga 

 must give (obi. + velu. ) X (Lam. -fvelu.) = obi. XLam.-f obi. Xvelu. 

 -j-velu. X Lam. -f-velu. Xvelu. = 25 per cent empty grains-f25 per 

 cent oblonga + 2$ per cent Lamarckiana-\-2$ per cent empty grains. 

 The expectation is therefore for two t>pes and these in equal pro- 

 portions. The two t>pes always appeared, and no others besides 



