Listen up stonermonkeys - this shit is indeed complicated and it takes a trained molecular biologist to do such things. Basically you are transforming the gene for the enzyme that makes THC from another starting compound. In other words you can put the THC synthase gene into another plant. Second of all, since this gene is now incorporated into the genetic material (the DNA) of the new plant, it will pass it on to its offspring. It has all been done actually by some Japanese biologists check it out here if you can get access (you might need to use a university computer system that has the journal subscription.) It's interesting stuff but not really practical for just anyone to do. Further, I'm sure it would be possible to make any plant capable of producing THC illegal, and also I doubt it all plants would prove to be effective hosts for this process.