THC content

I was going to post this to a recent thread on a similar subject but it just seemed too much of a hijack.

My question is, how is it possible for marijuana to contain the extremely high percentages of THC that we hear about in the news? Such a thing doesn’t seem possible in nature. My WAG is that the growers, after cutting the plants, hang them upside down for awhile and this causes most of the sap, which contains the THC, to concentrate in the tops. I can see how that could cause the high content.

But in that case, what do they do with the “bottoms”? Do they just throw them away, or do they reach the street as low-grade pot?

[Disclaimer]I have no intention of trying any of the above at home, nor do I recommend anyone else to do so. I just want to know. [/Disclaimer]