ANDROLETHAL FACTORS IN OENOTHERA. 



The genetic behavior of Oenothera biennis and 0. syrticola (0. 

 muricata L.) as uniform and constant species is now generally ex- 

 plained by the assumption of the presence of two gametic lethal 

 factors. The reciprocal hybrids of these forms are unlike each other 

 and the double reciprocal hybrids return to the grandparental types. 

 It is assumed that there are two kinds of gametes, but that one 

 of them is killed in the pollen and the other in the ovules. In fertili- 

 zation the two kinds would meet, producing a complex constitution 

 not unlike that of dioecious and heterostylous and of numerous 

 selfsterile plants. 



In tracing a pedigree of 0. Lamarckiana and its best studied rela- 

 tives Boedijn proved that 0. biennis is probably a derivative from 

 that species, whereas 0. syrticola belongs to another branch of the 

 pedigree-tree. If this is true, the presence of analogous gametic 

 lethals on such distant lines would indicate a more general occurrence 

 in a latent condition. This supposition would be supported by the 

 fact that of late a high degree of latent mutability has been found 

 to exist in 0. biennis. Among the mutants of 0. Lamarckiana the 

 apparition of gametic lethals is a common phenomenon and might 

 be regarded as in some way connected with such a general latent 

 condition. 



As a matter of fact, however, 0. Lamarckiana itself is not known 

 to contain gametic lethals. Its reciprocal hybrids with uniform 

 species embrace the same types. On the contrary it has two zygotic 

 lethals, which kill the germs within the young seeds, whenever the 

 same lethal enters that germ from both parental sides. This pro- 

 duces the empty seeds, which in this species amount to one-half 

 or more of the total number. Of these zygotic lethals one is linked 

 to the broad foliage and other characteristics which become apparent 

 in the hybrids of the type laeta, while the other is connected with 

 the narrow leaves and other marks observed in the velutina hybrids. 

 In selffertilization the amphilaeta and the amphivelntina germs will 

 therefore be condemned to an early death, whereas only the com- 

 bination laeta x velutina will produce viable individuals, reproducing 

 the type of the parent. These zygotic lethals are assumed to be 



