Q.Christmas Cactus
I have a 100 year old cutting of a Christmas cactus. I was told to just put it in water and it will root. It has been in water at least 3 weeks now and nothing is happening.

Certified GKH Gardening Expert
These plants are typically propagated using soil. Don't try to root your cuttings in water - they'll turn into a slimy mess and chances are you'll just be wasting your time.
This article will help: https://www.gardeningknowhow.com/ornamental/cacti-succulents/christmas-cactus/how-to-propagate-and-plant-christmas-cactus.htm