436 Genetics of Sex Determination 



showed, it is a basic error to treat female and male heterogamety 

 alike, and this applies also to plants. In one of the best analyzed 

 cases of intersexuality in plants, Rumex acctosa (Ono, 1935), with 

 male heterogamety, it is completely certain that sex determination is 

 identical with that of Drosophila. Here, also, combinations with differ- 

 ent numbers of autosomes and X-chromosomes show that the F factors 

 are located in the X-chromosomes; the M, in the autosomes; that the 

 balance F/M decides sex or intersexuality; that the Y-chromosome 

 here does not take part in the balance mechanism; and that probably 

 only two autosomes contain the male determiners. If it should turn 

 out, as will be demonstrated later in detail for Melandrium, that the 

 Y-chromosome may enhance the F/M balance, based upon X and 

 autosomes, in favor of M, this would be an additional problem paral- 

 leling the influence of Y heterochromatin upon other genie actions, as 

 discussed in detail in the chapter on heterochromatin. Thus it is con- 

 sidered certain that with female heterozygosity the F determiners may 

 or may not be located in the Y-chromosome; but this in no way favors 

 Correns' old formulation (which was made for a case of male hetero- 

 gamety), since the analysis of intersexuality shows that the F/M 

 balance is decisive with both F and M present in each sex, and is 

 not a simple dominance relation, as Correns assumed. It is further 

 certain that in male heterogamety, M must be located in the autosomes 

 (or eventually in the cytoplasm), which does not exclude male en- 

 hancers in the Y, as we shall see. 



In discussing the genetics of sex determination in some dioecious 

 flowering plants, it must be kept in mind ( as also Hartmann and Wes- 

 tergaard intimated) that we are dealing with a situation which is 

 basically different from that in Lymantria and Drosophila, and many 

 other animals. These are real sex-dimorphic species in which each cell 

 at any stage of life is either completely female or completely male. 

 Intersexuality therefore means stoppage of female determination dur- 

 ing the individual development and replacement by a male one, or, as 

 I have called it, a mosaicism in time. But the plants in question are 

 basically hermaphrodites in which the anlagen for both types of sex 

 organs are present in different positions in the flower, and frequently 

 are even visible as rudiments in the intersexual flower. In a female 

 the female organs will always occupy the place they would occupy in 

 a monoecious flower, and vice versa, also the male parts. A somewhat 

 parallel situation is found in the vertebrates, where both gonads and 

 ducts are first laid down with the anlagen for both sexes, and one set 

 or the other is more or less suppressed during development. It is to be 



