My guess would be that the water wasn't holding enough oxygen. A container that's too narrow at the top, too deep/not wide enough, stuffed too full, etc, doesn't have enough surface area for oxygen to be exchanged at the surface of the water. Too little O2 means the cutting can't root, and eventually rots.

Using a container with a wide mouth, and keeping the water level wider than it is deep will facilitate O2 exchange. Changing the water daily, and/or aerating it manually several times daily (shaking, swirling, stirring) also helps.

Good luck with the new shoot.

Posted by kwie2011 8a w. OR (My Page) on Sun, Sep 14, 14 at 16:55

I was using a container with a wide mouth, and keeping the water level wider than it is deep. The entire glass jar has only this one cutting sitting in it. It refuses to root for 2 years. Over the last month, August 2014, the main branch disintegrated in water and roots started to grow out from a secondary branch attached to the previous main branch.