Try rooting the bottom bit, just as is.

Harrisia ×jusbertii

Royston Hughes had the Maihueniopsis. The stall with Martin Lowry on was filled with plants from Maurice Williams' collection.

It doesn't look hollow. When they're completely rotten inside the roots tend to pull away with most of the innards at the same time. I'd give the stump a scratch with a fingernail or a brush with an old toothbrush to check for clean tissue. I suspect that would be all you'd need to do but you could ...

There's an easier way! https://www.cactuspro.com/lecture/Ashin ... ge-22.html

The group has several admins and I would recommend raising concerns like this with one or more of them in the first instance.

http://cactus-de-patagonia.de/samenliste is online.

It is, yes!
https://bcss.org.uk/product/cactusworld-2023-4/

https://adblps-graines-cactus.com/commander_EN.html is updated.

A pair of the curved style of these can help to guide it upright again: crucible tongs