We're all just a bunch of big walking greenhouses

When I was a kid, my great-grandmother would always tell me I shouldn't swallow seeds or pits. She'd say it would make a plant grow out of my head.
I assumed she was joking, but still got a kick out of the mental image of a cherry tree growing out of my skull. Or maybe a few nice strawberry plants. Add some raspberries and I could have tasty vitamin-packed snacks whenever I wanted.
How convenient!

Then, many years later, mom told me about some kid who really DID have something growing in his skull. He was dumb enough to stick a kidney bean up his nose, and the bean started sprouting in his sinus cavity. (Accgghh! Shudder! Twitch! Twitch!)
If I remember correctly, they had to surgically remove it.

And then, I happened to find this story about a grown man who had a fir tree growing in his lung. (!!!) The story says he apparently inhaled a small bud, and it took root. They had to remove that section of his lung. Click on the link for a rather disgusting picture of it.
Here's the part that makes me a little confused:
How did it grow without sunlight? I can see how it would have had plenty of nutrients and moisture, but don't plants die without sunlight?
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