A. B. Stout - 127 



In hermaphrodites maleness and femaleness are both qualities 

 possessed by all cells. Any nuclear organization or combination resulting 

 after reduction division can become male or female according to whether 

 the cell lineage leads through stamens or pistils. The obvious differen- 

 tiation of the two sexes, morphological and physiological, may begin in 

 the development of entire branches, or of flowers as wholes, or of stamens 

 and pistils of the same flower, and is at first strictly a somatic differen- 

 tiation of like diploid cells. The sexual nature of these sporophytic 

 structures is however seen in the intimate part which they play in the 

 production and function of the haploid sex generation. 



A self-incompatible plant is itself the result of a compatible fertiliza- 

 tion. Cytoplasmic and nuclear elements of an egg and a sperm fuse to 

 form a zygote highly vigorous and of high sexual potentiality, yet its 

 sex organs fail to function together. The elements which were com- 

 patible in the fertilization and in the life of the resulting zygote became 

 incompatible during ontogeny. Yet the incompatibility does not arise 

 simply because of the element of constitutional similarity involved in 

 hermaphroditism, nor because of sex-differentiation as such, for a sister 

 plant with the same parentage and ancestry may be highly self- 

 compatible. 



Sexuality is a cyclic recurring condition which makes possible the 

 fusion of cells and nuclei and the pairing of chromosomes. The incom- 

 patibilities exhibited in processes of fertilization are due to physiological 

 properties that are acquired during sex differentiation. 



Whether the most successful fertilization depends on some element 

 or degree of similarity, or on some degree of dissimilarity, or on a proper 

 balance of the two, it is clear that the behaviour of incompitibilities 

 both self and cross gives no proof that unlikeness in the sex organs 

 favours the union of gametes, or that some element of similarity leads 

 to incompatibility. 



New York Botanical Garden, 

 Mai/ 29, 1919. 



