It looks like it is in the wrong kind of soil. I would repot it (using the same pot) with a sandier soil mix, making sure that it gets good drainage. The only possible problem I see here is over watering, but it's not dead yet. Get rid of as much of the old soil as possible without damaging the roots, and check for root rot. Cut off any rotted roots.

Magpie, this title should be in a C&S publication headline. Caught my attention that's for sure!

As Lars had mentioned, I'm afraid you have to pull a mini operation and dissect one of the stems to observe for rot. If you anything brownish, it's rot and the infection is real. I'm not sure about cacti but I think you can cut it till you stop seeing the rot, let the wound heal/callous over and replant it into a well draining mix. Roots should regrow in about a couple weeks to months.

Make sure you give some research on well draining soil while your cactus is callousing. It can take a couple days, so you'll have time to assemble your new mix.

Good luck.

Wow, having grown kids, that caught my attention, too, a little too real for me. My son NEARLY disowned me for killing his lemon tree that he grew from a seed in his bedroom without parental approval. :) Anyway, on my plants that are super special for some reason like that. I propagate them and have several before it becomes critical. Just looking at that, it looks like you have plenty of material there to work from. I am betting and hoping the cactus makes it. Please update with the happy ending.

Thanks for the advice-- she's following the thread. I didn't come up with the title-- I just cut and pasted her sentence in her message. :)

Rot rot rot really thank god for cacti specialists because that's not rot. Tell your son his plant will be fine,that's corking happens with age and or old soil. You could leave it as it's been or make a cactus mix,commercial potted cactus soil,perlite and expanded shale or just cactus mix. For all of you that though it was rot,the whole plant could of been killed for no reason.not bashing any of you I've killed many of my plants thinking they had rot so it's not y'all's fault! I'll leave some links,rots not always rot.http://cactiguide.com/cactipests/

http://www.trichocereus.com/disease2.htm

http://www.trichocereus.com/tip_pimples.htm

Thanks for the info spike! Never planted cactus before, so I'm still learning. I'm just using my knowledge from growing succulent and implementing it here.

Bernard

That is corking and, to me, it looks stressed from high light and under watering.... First things first: I would, definitely, check the roots and see if it doesn't have invaders like mealie chomping on em. Pulling it out of the soil won't hurt this plant. The current mix looks peat based that's possibly no longer absorbent. Could be wrong on this, but, I'd repot in fresh mix, anyway. A fast draining blend with 50% pumice and or perlite to soil. Reducing the variables of what can be wrong by making sure most of its culture is right will take some of the guess work out.

It looks like an echinopsis - possibly white flowers? They are forgiving and with the right culture and time it recovers well.

Perhap, magpiepix, you could tell us if the base of these stems is soft and hollowish or are they solid with little give?

Link is unknown, Spike. I'd like to read the material if you fix the link.

Ok fixed the links, all of you including deva I know 100% that's not rot it's corking. Aztcqn your probly right but I could just be old age. Replanting cacti is almost like replanting any other potted plant.

Spikef22/noah