Different Genetic Possibilities within the Balance Theory 439 



the X-chromosomes controls the sex; the Y-chromosome is not in- 

 volved. In Melandrium, in contrast, the presence of a Y always de- 

 termines males, and its absence, females, whatever the autosomes and 

 X-chromosomes (except no. 22). Thus the Y-chromosome is here so 

 strongly male-determining that it looks as if the autosomes and X-chro- 

 mosomes do not play any role, and no balance mechanism is present. 

 But no. 22 (from Warmke) shows that the X-chromosomes do con- 

 tain female determiners of such weakness that, in the presence of Y, 

 four of them are needed to make this influence felt. Hence the decisive 

 fact that was missing in Bombyx is established here. 



The presence of female determiners in the X-chromosomes without 

 a balance mechanism seems queer; we know (see above, Strasburger; 

 and below, gynomonoecism ) that females (without Y) can develop 

 male characters. Relevant for the solution of these contradictions are 

 further data by Westergaard. From crosses between triploids, females 

 and males were obtained as before, and in addition some hermaphro- 

 dites (intersexes; see below regarding this nomenclature) having a 

 Y-chromosome. These, then, are andromonoecious: usually the first 

 flowers are intersexual (hermaphroditic); the next ones, low inter- 

 sexual; and the last, male. It was noticed that this result was found 

 mostly in the presence of three sets of autosomes. Since all these 

 intersexes could be selfed, analysis of many combinations becamxO 

 possible. One important point is that by selection of "androhermaphro- 

 dites" ( or weak male intersexes ) , real hermaphrodites ( or higher grade 

 intersexes) could be established. Without going into further details, 

 the conclusion was reached that bisexual plants, that is, subgynoecious 

 males in the presence of a Y-chromosome, are determined by the num- 

 ber of X-chromosomes and the combination of the autosomes. Table 6 

 illustrates this. 



The table shows that the percentage of "intersexes" increases from 



to 100 per cent when the number of X-chromosomes increases from 



1 to 4. Since plants with identical constitution in regard to sex chromo- 

 somes may develop into males or intersexes, the cause must be sought 

 in the only variable left, the combination of autosomes. Thus it follows 

 that the X-chromosome acts in the female direction, and some auto- 

 somal combinations can enhance the pull in the female direction. 

 Westergaard thinks that this role of the autosomes means that some 

 autosomes are female-determining. Further, he assumes that the more 

 female-determining combinations in the aneuploid types are originated 

 by a "changed individual equilibrium" between female- and male- 

 determining autosomes. Such an equihbrium change could occur in 



