1907] DE VRIES—TWIN HYBRIDS 



407 



4 



Others is independent. But I must 

 ments on this point for another occasion 



reserve 



SUMMARY 



!• Hybrids between members of the group Onagra or the O. 

 biennis group of the evening primroses are, as a rule, constant in 

 succeeding generations. An exception is O. brevistylis, the char- 

 acter of which follows Mendel's law. 



2. The reciprocal hybrids of this group are, as a rule, unlike one 



^ + - 



another, and mostly patroclinous. 



3. In many cases, where O. Lamarckiana or one of its derivatives 

 is the father, two forms of hybrids are produced instead of one. These 

 forms may be called twin hybrids. 



4- One of the twins is broad and smooth-leaved and is called O. 

 laeta; the other is more hairy and has furrow-shaped leaves, and is 

 designated as O. velutina. 



5- O. laeta and O, velutina are produced by the combinations O. 

 biennis X Lamarckiana and O. muricataX Lamarckiana, and by those 

 of some of their derivatives, 



6. They are produced in about equal numbers. 



7. They remain constant in the second generation. In the only 

 ascertained case they also showed themselves so in the following 

 generations. 



Amsterdam 



