

1907] DE VRIES—TWIN HYBRIDS 



403 



cata and O. biennis in their subspecies from our European dunes. 



mig 



for it, since it is broad-leaved and large-flowered. The O.hientiisX 

 muricata, on the other hand, is narrow-leaved and small-flowered 

 like its male parent. During the summer of 1907 I cultivated the 

 first and second generations of the latter type and found them uniform, 

 but in almost all respects different from the O.muricataX biennis. 

 Especially the flowers are of a deep yellow and strongly scented, 

 while those of O. muricataXbiennis are pale and faintly scented. 



This difference between the reciprocal hybrids is also clearly 

 manifest in the crosses of O. Lamarckiana with the types of our dunes. 

 The O. LamarckianaX biennis has been described in my Mutations- 

 theorie (2:31) for two generations, the third having only been culti- 



r 



vated in 1907. The O. LamarckianaX muricata has been described 

 and figured in the same volume (see page 29), but I have not as 

 yet succeeded in getting a second generation, partly on account of 

 the weakness of the type and partly on account of the general phenome- 

 non of strongly diminished fertiUty in all these primrose hybrids. 



The reciprocals of the two hybrids just mentioned afford the 

 curious and rare phenomenon which I call that of the twin hybrids. 

 In crossing one spike of O. biennis with the pollen of one plant of O. 

 Lamarckiana, one does not get one but two hybrid types. The same 

 holds good for O. muricata. These forms are intermediates between 

 the parents and almost alike when seen from a distance, but sharply 

 distinguished when closely examined. These differences are the 

 same whether O. biennis or O. muricata is the mother plant, the 

 hybrids showing their divergent origin only in apparently sub- 

 ordinate marks. One of the twins has broad and flat leaves 

 of a bright green: I call it O. laeta. The other has narrow, more 



furrow 



green, which are more 



ry, and is therefore designated O. veluiina. These same names 



may 



occur 



The twin hybrids, O. laeta and O. velutina, occur in numerous 

 hybrid combinations where O. Lamarckiana or one of its mutants 

 is the pollen parent; as for instance with O. brevistylis, O. rubriner- 

 vis, and O. nanella. In these cases they drop, at least in the first 



>¥ 



