But wait why is it on a circadian cycle? "BUT what appears to be even more important to the plant is staying on a 24 hour circadian rhythm. Plants have receptors in their leaves that are used to regulate their hormones according to what time of day (or night) the plant 'thinks' it is."
Are you sure about that? Does the plant "think" its a certain time of the day by the actual time? I thought it "thinks" its a certain time of the day by the light. When it gets flooded with light in the morning, it must be morning. When its dark its night. As long as you still have a 12 hour night cycle it would allow the FT to get up above the threshold level to induce (or continue) flowering.
What they did to show this was to take some plants (that flower just like cannabis) - put them in long periods of darkness, and then would randomly flash them with some light at different times and measure the response biochemically. What they found is that even though the plants were in darkness for extended periods, they were still staying on a 24 hour hormonal rhythm and that the response to the light flashes would vary according to whatever time of day the plant thought it was still on (within a 24 hour cycle). Even though the plant was in total darkness it continued right on with assuming it *should* be day or night at certain times within a 24 hour cycle.
What that means is that plants have a twenty-four hour circadian rhythm (like most living things on earth) that isn't entirely dependent on just the rising and setting of the sun or the length of daylight. It was previously thought that 'sensors' in leaves, called phytochromes, were responsible for telling a plant when the day/night cycles were long or short enough that they should flower. But like the above experiment showed, these phytochromes are actually not primarily responsible for regulating hormones (like FT). Instead, it's been shown that plants use phytochromes simply to orient themselves to where they are on any 24 hour cycle... but in the end, they are programmed to stay on a 24 hour rhythm despite changing day/night schedules.
But you are right, if a flowering plant like cannabis gets at least 12 hours or so of uninterrupted darkness, it will begin to flower. That darkness could be 12 hours or it could be more - it will flower as long as the dark periods remain over 12 hours or so in length. However the plant is still going to plod along on a circadian rhythm and assume that if there is 12 hours of night there will be 12 hours of daylight (or close). So if a plant were given 12 hours of darkness and say 24 of light in a 'day' then half way through the daylight period the plant will begin to assume night is coming and chemically prepare to switch from producing sugars with photosynthesis to consuming sugars during the expected absence of light... and the overall benefit of an extended light period will be minimized.
Over a period of time, the phytochromes, and the hormonal responses they time-keep for, will eventually cause the plant to try and readjust when it assumes day or night will start... but the plant will just be spinning it's wheels because it is hard-wired to be on a 24 hour cycle regardless of anything else.
The result is continual hormonal confusion within the plant that makes the extra light periods inefficient. And possibly confuses things enough to result in stress and awesome things like hermaphroditism.
