1919] DeVRIES— OENOTHERA RUBRINERVIS 25 



Crosses with O. ruhrinervis also yield the expected result. This 

 would be in one direction (obl.+velu.) X(deserens+velu.) =obl. X 

 des.+obl. Xvelu.+velu. Xdeserens+velu. Xvelu. = 25 per cent {obi. 

 Xdes.)-]r2$ per cent oblonga-\-2^ per cent ruhrinervis -\- 2^ per cent 

 empty grains. I have not as yet tried the cross between O. ohlonga 

 and O. deserens, however, and thus must leave undecided the ques- 

 tion as to which characters will dominate in this hybrid. As a 

 matter of fact, I found 20 per cent ohlonga and 80 per cent ruhriner- 

 vis and no other types. The reciprocal cross must give (des.-f- 

 velu.)Xvelutina = des. Xvelu.+velu. Xvelu. = 50 per cent ruhriner- 

 vis-\-$o per cent empty grains. Only ruhrinervis have been 

 observed in this culture. 



Crosses with the pollen of O. biennis must give ohlonga Xhiejtnis 

 -\-velutinaX biennis. The former is intermediate between the par- 

 ents, whereas the second is the same as the hybrid type Lamarckiana 

 Xbiennis. I found in one cross 65 per cent ohlonga (partly dwarfish)' 

 and 35 per cent hybrids of the second type. In another instance^ 

 however, the ohlonga failed from some unknown reason. 



With those species which ordinarily produce the twins densa 

 and laxa the pollen of O. ohlonga must evidently give only the latter 

 type. This has been the case in three trials with O. biennis Chicago> 

 and in one with O. atrovirens {cruciata). 



For further details and for the constancy or splitting in the 

 second generation I must refer the reader to the pages of my book 

 already quoted. These results, however, show clearly that all the 

 facts hitherto ascertained confirm the formula assumed for the self- 

 fertihzation, and thereby the analogy with the phenomena observed 

 in O. ruhrinervis. 



Summing up this discussion we may say, therefore, that O. 

 ohlonga arises through a mutation of the typical sexual cells of 

 O. Lamarckiana, leaving the velutina gametes and also the lethal 

 factors unchanged, but producing, besides the externally visible 

 marks of the mutant, a suppression of the mutated pollen grains. 



On the other hand, O. mut. nanella seems to arise through 

 mutations in the velutina gametes of O. Lamarckiana, as is shown 

 by the fact that the laeta do not split off dwarfs, whereas the 

 velutina regularly do so. The figures given in my book for the 

 crosses with O. nanella may be calculated in the same way, and 



