Julie

I just threw out that idea because of a discussion on another forum concerning the same thing. From what you've said, it does sound like a light issue. Either way, when the outer cells of the leaf are damaged, it looks like that kind of collapse can occur. It makes sense.

On this other forum, we were once discussing why a person was having problems with spikes on phals suddenly collapsing. It turned out that water condensing on the roof of the GH was dripping and hitting the spike on one spot. Since it was winter at the time, the water was cold and caused the same kind of cell collapse on the spike.