Correns'' hypothesis of sex potencies and sex tendencies is applied to dioecious angiosperms. Sex-potency factors are probably borne on autosomes; sex-tendency factors may be borne on allosomes. There are also many sex-influencing factors, some of which, as well as environmental factors, at times produce results comparable with those of sex-tendency factors. In bryophytes, environmental factors produce effects more or less like those of sex-influencing factors, but they are not shown to reverse the sex expression of a dioecious species, as is the case in angiosperms. All known facts indicate that in dioecious bryophytes a haploid gametophyte is and can be only 3 or only ?. In haploid hermaphroditic bryophytes, each plant may have a ^-determining and a $-determim''ng factor. By loss or chromosomal interchange, a dioecious form may arise, each plant then having only a ?- or a ^-determiner, borne respectively on an X or a Y chromosome. Diploid hermaphroditic forms, possessing both X and Y chromosomes, have been produced experimentally from haploid dioecious species, and have probably originated similarly in nature.