Aside: It's called nine-bark because the bark peels off, showing several layers at once.
Other branches bear only green leaves, and green-budded flowers, thus resemble the wild-type of the species, if that's the correct term. It seems that whatever genetic change(s) resulted in the creation of a purple-leafed form is switched off in some branches (where, both anatomically and cellularly, I don't know.) Any plant geneticist out there who can explain this?
In any case, it is an attractive plant, but it grows very fast, reaching twelve feet within a few years. It has long, arching branches that reach over fences and have the potential to irk neighbours who fiercely defend their airspace. Just thought you should know. (I spend a lot of time pruning.)