Darling: Sex in dioecious plants 195 



Gastle ('09) explains sex determination as dependent upon the 

 presence of a factor or factors which are inherited in accordance 

 with Mendel's law. Femaleness is due to the presence of this 

 factor or factors and maleness to its absence. The differential 



m 



factor is transmitted in two ways: (i) The differential factor is 

 doubly represented in the female^ which is homozygous, /. e., gives 

 rise to similar gametes. The male, characterized by but one 

 differential factor, is heterozygous, /. ^., gives rise to two gametes, 

 one possessing and the other lacking the differential factor. Sex 

 determination therefore rests with the male parent, for when ferti- 

 lization" is effected by the male gamete possessing the differential 

 factor males result The female is homozygous dominant, not, as 

 Correns supposed, recessive ; while the male is heterozygous 

 dominant, pure recessives being unknown. (2) The differential 

 factor appears in but one of the gametes, /. ^., the egg. There- 

 fore sex must be determined by the female (egg) since the male 

 does not carry the differential factor. The female is heterozygous 

 dominant and the male is homozygous recessive ; homozygous 



dominants are unknown. 



I desire to express my hearty appreciation for helpful suggest- 

 ions and criticisms to Professors C. C. Curtis, E. B. Wilson, and 

 T. H. Morgan. 



Columbia University, 



March 22, 1909. 



Literature 



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 Cardiff, I. D. '06. A study of synapsis and reduction. Bull. Torrey 



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