496 HEREDITY AND SEX 



that the X-element contains factors (enzymes or hormones ?) 

 that are necessary for the production of both the male and the 

 female characters ; that these are so adjusted that in the presence 

 of a single X-element the male character dominates, or is set 

 free ; while the association of two such elements leads to a 

 reaction which sets free the female character. 



8. Fourth Theory : That Maleness and Femaleness are 

 Mendelian Characters 



A Mendelian interpretation of sex, first suggested by 

 Strasburger, has been developed by Castle, Correns, Bateson, 

 and others. As Prof. Wilson points out, the interpretation 

 has taken " three forms, which exhaust the a priori possibilities. 

 These are, first, that both sexes are sex-hybrids, or heterozygotes 

 (Castle) ; second, that the male alone is a heterozygote, the 

 female being a homozygote recessive (Correns) ; third, that the 

 female is the heterozygote, the male being a homozygote re- 

 cessive (Bateson) -" 



As Prof. Wilson has shown, each of these forms of the theory 

 has its special difficulties, which seem to be most serious in the 

 case of the first. 



* 



Prof. Correns's theory was based on beautiful experiments 

 in crossing dioecious and monoecious forms of Bryony, which 

 showed that the monoecious condition behaves as a unit char- 

 acter, which is recessive to the dioecious. 



The experiments made by Correns go to show that the pollen- 

 grains of the dicecious Bryony, though apparently all alike, must 

 be regarded as of two kinds in equal numbers male-producing 

 and female-producing. What immediately arise, as a matter of 

 fact, are the rudimentary male prothallia, which produce the 

 reproductive gametes or pollen-nuclei, and the egg-cells fertilised 

 by half of these produce male plants, while the egg-cells fertilised 

 by the other half produce female plants. 



