I am pretty sure this is caused by old branches or suckers not pruned close enough, and then healing over after several years of further growth.

Referring to your recent post:

There is a type of ginkgo tree called chichi ginkgo (these are very old trees not the chichi ginkgo found in catalogs today) that has long knobby growths. These knobs hang down with age and chichi means breast in japanese. Anyway, the point is that these knobby growths turn out to be air roots. When they reach the soil they root in and can even start another tree. The chichis on these old ginkgos look a lot like the knobs on those fig trees.

Susan

You might want to put some Compound W on the tree with the two pics on top. Looks like it's got warts.

Hmmm, strange.  Looks just like my MIL's thighs. 

Jason, don't let your daughters hear that. They may worry about their genetics and what is in store for them.

One could stare at that for a few minutes and imagine all kinds of body parts (that you really don't want to see). 

I see what you're talking about Cathy

Yeah, one of the big-name designers was actually pushing out a line of white porcelain or ceramic candleholders and other stuff with boobies all over them - I want to say it was Todd Oldham - it reminded me of those too, but the MIL was in town this weekend, and that was a lot fresher on my mind.

@Jon, thankfully my wife dodged the bullet, so maybe it's not genetics ;)