350 Proceedings of the Ohio State Academy of Science 



activity of chromosome groups, of individual chromosomes, or 

 of smaller heredity-bearing units. 



5. Hereditary tendencies may be dominant or recessive in 

 respect to each other; they may be dormant or active through 

 the influence of environment ; or they may work together or 

 influence one another in such a way that a strange or new 

 structure appears. 



6. • Sexuality expressed as maleness or f emaleness, whether 

 in gametes, sexual organs or individuals is a condition and not 

 a character, and the development of a cell as an egg or a sperm 

 does not destroy its power later, parthenogetically, to produce 

 the opposite sex. 



7. Fertilization was primarily not a stimulus to further 

 growth ; conjugation was primarily not a mode of reproduction, 

 nor was sexuality primarily developed as a means to variability. 



8. Sex may be determined sometime before reduction and 

 thus independently of any process going on during either a vege- 

 tative or reduction karyokinesis ; it may be determined during 

 the reduction division; it may be determined during the fertiliza- 

 tion stage; or finally it may be determined after vegetative 

 growth has begun. 



9. <• In some cases, when the sex is once determined it can- 

 not be changed in the vegetative body nor in any negative spore 

 or propagative bud ; in other cases, it may be changed in the 

 vegetative body after being developed as male or female. 



10. ♦ The sexual ratio is not Mendelian in the gametophyte 

 and apparently not in the sporophyte. 



11. The most prominent fact in the differentiation and 

 evolution of unisexual gametophytes in the higher plants is that 

 although the entire mechanism of reduction was well developed, 

 nevertheless the separation of the sexes was accomplished en- 

 tirely independently of reduction by a differentiation of large, 

 female-determining, and minute, male-determining spores. 



