this is not true, THC is NOT produced in the roots, stem or leaves even, THC is produced at the tip of the trichrom where the stalk meets the head. it would be kind of silly for it to make it anywere else, than it would need to spend lot of energy getting it there... and than figure out some crazy way of getting it in the ball head of the trichrom, which is made of only 8 cells, sometimes slightly more, or less. purple or red stems are the cause of genetics or grow conditions seems, I wouldnt worry about it unles the plants show other signs of illness