I notice the same thing with my xenia frag. It's about halfway up the stalk. It appeared about a week after I picked it up from KingEd's. Almost looks like loose skin. Doug maybe right cuz I watched it for awhile as it swayed with the current, and noticed how that particular area was reaching out towards a rock that was beside it. Maybe it's trying to branch out. I've only had this frag for 3 weeks now, and it has grown to almost twice the size of when I first bought it. Hope it's not dying tissue on my part because it does look healthy.
Rich