In ancient times, when a man lost his leg, the village folk would hike out to collect the stems of the cannabis plant.

It was long, tiring work and little appreciation was shown by the legless man in question, often crying very loud in total anguish.

By nightfall of the fourth stemcollecting day, or "stemsday", the great fires would be lit in the town centre, and all would work together on binding the stems together real tight, until the break of dawn.

"Behold your leg of stems, legless man, for it is woven by us in your name" they would cheer repeatedly.

The leg of stems would then be dipped in rooting hormone, and attached to the man's stump by the village elder.

To make a long story short, if you have enough stems to make a wooden leg out of them, you could attach it to your body and harvest your own personal symbiotically grown marijuana.
Then you could say "MJ doés grow on my back"