Well, I for one, after reading this thread and checking various other resources that I didn't track because I didn't prepare to present my findings, believe that seeds are predisposed to be one sex over the other; but that a plant can change sex entirely based on environment.
There are common threads throughout the theories surrounding the argument that environment effects sex. Everything that I have read dealing with environment effecting sex suggests that highland plants are more likely to grow males while lowland plants are more likely to grow into females.
Some more research:
" Although genetic factors dispose a plant to become male or female, environmental factors including the
diurnal light cycle can alter sexual expression."
Cannabis sativa - Wikipedia, the free encyclopedia
I added the [citation needed] in hopes that someone will soon edit the page and add a citation. That would settle it once and for all. But I think this is enough information to go on, really.