I have seen pretty much the same thing as what Kyle's picture shows, but those plants affected are always in or coming out of dormancy. They are kept dry and basically in low light/sunless. I have never been able to understand why exactly. I call the condition "dry-rot". The stems are always firm and there is never any mushy part. When I cut into the stem it will be solid as a rock and unfortunately, more like a rock than living plant tissue. There is no "latex" oozing. There is simply no viable tissue whatsoever. I generally lose these plants since by the time they are discovered (spring), it is far too late to salvage anything. I have already discovered (and trashed) a single, branched plant. It was in the center of probably two dozen mature, potted plants in my temporary greenhouse. All the other plants look fine.
