DETERMINATION AND INHERITANCE OF SEX 549 



entirely different matter from the position that Correns takes that sex 

 is fixed at the time of fertilization and determined by the spermatozoa. 

 Correns made his experiments with two species of Cucurbitacese, 

 the family to which our pumpkin and squash belong, growing wild in 

 central Europe. These two species are Bryonia alba and Bryonia 

 dioica. The former is the plant which supplies the root employed in 

 pharmacology for the treatment of dropsy. The especial value of 

 these species for experiments relative to the problem of sex, lies in the 

 fact that the former is hermaphroditic or monoecious, i. e., mature 

 male and female flowers appear on the same plant; and the latter is 

 diecious, i. e., male and female flowers appear on different plants. 

 These two species can be crossed in either direction. Correns made 

 three sets of experiments, the results of which have led him to a unique 

 and simple explanation of the cause of sex, in the light of which former 

 theories must undoubtedly be more or less extensively modified. Cor- 

 rens first crossed Bryonia dioica with Bryonia alba, using the eggs of 

 the former and the pollen grains of the latter. Sterile hybrid-offspring 

 appeared from the cross and they were all females. Correns explains 

 that since germ-cells of the hermaphrodite forms carry only herma- 

 phrodite determinants, the male gametes (pollen grains) can have had 

 no influence on the sex of the offspring of this cross. In other words, 

 hermaphroditism is recessive to dieciousness. And since the offspring 

 were all female, all the eggs of Bryonia dioica must have had female 

 tendencies. 



Correns next pollinated the pistils of Bryonia dioica with the pollen 

 of the same species. Forty-one pure dioica offspring were obtained 

 from this cross, twenty-one of which were female and twenty male, or 

 in round numbers each sex appeared in 50 per cent, of the individuals. 

 Since the eggs were all female, as shown by the first experiment, this 

 result must mean that the pollen grains determine the sex and that 

 they must be of two kinds, male and female in tendency, and approxi- 

 mately equal in number. It must also mean that the male tendency 

 dominated over the female, else no males could have appeared. 



In a third set of experiments the pistils of Bryonia alba were pol- 

 linated by Bryonia dioica. The offspring in this case were sterile hy- 

 brids, and of the seventy-six which came to maturity thirty-eight were 

 male and thirty-eight female. This again shows that hermaphroditism 

 is recessive to dieciousness since no hermaphrodites appeared. It 

 shows also again that there must be two kinds of male gametes with 

 male and female tendencies, respectively, of equal number, and that 

 they determine the sex. It shows, moreover, that sex is determined at 

 the time of fertilization, for before that instant all the female gametes 

 (ovules) had the tendency to develop into hermaphrodite forms. It 

 appears also in the light of this experiment that hermaphroditism and 



