Shush,
Thanks so much. The bottom spot is more light than dark. It's more hard like wood than spongey like rot, but more like paper I would say, The 'vane' of the cactus is thin at the bottom and whatever this condition is, it runs right through the vane from one side to the other. I'm attaching another photo in close-up in cast that helps determine what it is. What do you think?
I was very interested to read your comment that the bottom cactus can use watering more often as a tropical. Crossing my fingers, hoping that means we've not overdone it.
