630 ANDROLETHAL FACTORS IN OENOTHERA. 



situated in the central chromosome, which also contains the factors for 

 almost all the recessive mutations of 0. Lamarckiana. They are 

 themselves recessive and are probably the cause of those curious 

 interchromosomal correlations, which are revealed by the disappear- 

 ance of the ordinary mutability from other chromosomes, whenever 

 they are absent. 0. Lam. mut. blandina, deserens, and decipiens are 

 destitute of zygotic lethals and do not contain empty seeds in their 

 capsules. Nor do they produce those numerous mutations, which 

 are so characteristic of 0. Lamarckiana, neither after selffertilization 

 nor after being crossed with one another. 



Of the mutations of 0. Lamarckiana, hitherto described, about 

 one-half are recessive, while the other half are dominant. These 

 latter are of a very complex nature, each of them embracing 8 to 

 10 or more hereditary units. Some of these elementary factors are 

 usually strikingly dominant, while others are of a recessive nature. 

 The term semi-dominant has been chosen to describe this condition. 

 On the other hand these complex factors may be compared with 

 the diagnoses of wild species, which ordinarily embrace a corres- 

 ponding number of unit characters and this comparison has led to 

 their designation as specific mutations. It is assumed that there 

 are seven main types of such specific mutants and that each of 

 these has its factors located in one of the seven chromosomes of the 

 haploid nucleus. The best known among them are lata, scintillans, 

 and cana and of these the two former are characteristic of two of 

 the three large chromosomes. In these there are, moreover, two 

 accessory mutant types, one of which, albida, is connected with lata, 

 whereas the other, oblonga, evidently belongs to the same chromo- 

 some with scintillans. Besides these, numerous secondary mutants 

 have been described, in which one or more of the units of the factor 

 complexes must be supposed to be in a different condition. 



From the great majority of wild species the specific factor com- 

 plexes of (Enothera Lamarckiana are differing, however, in two 

 essential points. These are the almost constant presence of an 

 androlethal factor and that of non-disjunction of the mutating chro- 

 mosome after the conjugation in synapsis. The first of these kills 

 in the pollen all of the gametes carrying the mutated characters. 

 It is thus to be considered as the cause of the fact, that none of 

 these specific mutations are inherited, in crosses, by means of the 

 pollen, but are transmitted only through the female gametes. The 

 factor for non-disjunction causes the doubling of the corresponding 

 chromosome and thus increases the total number of these rods in 



