Sorry NorCal - Sensiskunk is right and I know it because I've seen it and experienced it myself, not just read about it. However, I've also done a lot of research and confirmed my empirical understanding despite this being the area of MOST confusion and misinformation on the Web concerning growing cannabis.

Stressed females indeed can and do sometimes produce a few seeds, without the benefit of any male or "hermaphrodite" plant being in the area. Particularly strains that are Sativa dominant. This is an emergency measure at procreation from strains that probably originated in areas where there was some environmental reason for such a survival measure to evolve. In an indoor situation, stress can arise if for example (as happened to me) a fuse blows and plunges mid-flowering plants into darkness for several days before being detected. This "self-seeding" was an internal process, the plants were not "pollinating" one another, nor were the plants true "hermaphrodites", they did not have pollen sacs. They did not produce mad amounts of seed and the crop was not ruined.

I later grew a crop from those seeds and found that they produced 99% females and 1% Hermaphrodite - or a male, with female flower characteristics.

This is another common misnomer: a true Hermaphrodite in flower would show white hairs and bud type formations, like a female, but with sacs developing like a male and that COULD pollinate other nearby females therefore. But a lot of what people on these forums call Hermaphrodites, are NOT - they are just stressed females that self-produced a few seeds.