Lucky Bamboo Rehab
When a plant is injured or cut, it forms the plant equivalent of a scab - which seals the wound and keeps harmful bacteria from attacking. When you cut a stem like the lucky bamboo has, it first forms a scab, which then turns into a harder callous. This is normal.
You can see in the picture on the right that this bit of stem has put out a new shoot from the cuticle right under the callous. The sections of the stem which are under water will put out new roots, the sections which are above water is where new stems will appear.
Your bamboo needs new roots more than it needs new shoots a the moment, so immerse all but 2 of the cuticles in water. New shoots will appear at the cuticles circled in yellow in the picture below.
Virtually all new growth happens in most plants at the nodes where new leaves start to separate from the stem. The ring around the stem is called a "cuticle. It is where the old leaf base was attached to the stem.
In the picture below, the green circle indicates where a new cuticle will form when that leaf is no longer of any use to the plant. Notice that the stem is a darker green color than the leaf.
If you look at your other plants, the pothos and the monster, you can see that they have cuticles as well. Understanding the function of this plant structure is key to being able to do well with plants.
Your bamboo was in pretty precarious health. Rot, to a plant, is the equivalent of an infection in animals. The bamboo's roots had gangrene, and if the plant was to be saved all that old bacterial growth had to be removed and new root formation stimulated.
The approach I suggested to you was "covering all our bases". If we could stop the rot in the roots and get it to start growing new roots, then the bottom part of the old stems would live. However, if we could not halt the rot, it would be better to start an entirely new plant from a cutting - and that is what the top sections of the old stem are. If everything works, you will have doubled your viable stems from 2 to 4.
I think it might help to explain here not just what to do, but what you are actually doing and why you would want to do that.
Plants have a variety of ways of reproducing themselves, or more accurately "surviving" than just reproducing from seed. Every plant has a bunch of structures scattered throughout its stem, leaves, and roots which are capable of producing an entirely new plant.
When you separate a part of a plant from the other parts, it will start to go about the process of replacing what has been lost. It will draw on its own stored resources, just like animals draw on stored fat to get them through times of little food. In a plant, these are carbohydrates stored in the roots, stems, and leaves.
The leaves of a plant are where photosynthesis happens and where it makes its own food - carbohydrates. The roots draw up moisture from the ground, and trace nutrients which the plant needs. Take away either one and the plant needs to use up its stored carbohydrates to rebuild what has been lost.
The strategy that plants use makes a lot of sense when you think about it from a resource conservation point of view. The top half of your plants no longer has a root system, so it really cannot grow until it replaces it. This means that the old section of the plant where growth was taking place is now sort of excess baggage. Priority ONE is getting those roots regrown. Thus, when it comes time to steal those stored carbohydrates from somewhere, it makes sense to steal them from the leaves.
It is pretty analogous to what animal bodies do when stressed. If you are very cold, your body will pull blood flow back from your extremities to keep your internal organs warm.
That is exactly what this plant is doing. It can't support the old growing tips of the shoots (circled in yellow), so it is sacrificing them to the overall long term survival of the plant.
Notice how the older leaves lower down on the stalk (circled in green) are still green and viable. Photosynthesis is still happening here providing some food for the plant. The reason I had you cut the old dead portions off was so their health would be more apparent. These leaves will eventually die, but for the moment they are providing very valuable food to the plant that in needs to repair itself.
Ok, now what is going on in the picture below kind of worries me. It looks like we have not gotten the rot in the lower stem stopped. The roots on the stem on the right look pretty good, but the stem itself is still purifying. Now is when things start to get serious.
Wash the ends of the stems really thoroughly under a stream of water. If you have one of those sprayers on your kitchen sink, use it. Think of this as an infected wound on an animal. Clean it out as well as you can.
Get a razor blade, disinfect it on alcohol, and cut the very end off the stem on the right next to the roots - about where I have indicated with the green line. You want to cut off as much of the stem as possible but leave as much of the roots as possible. The roots look healthy and we don't want to force the stem to use up any more of its stored carbohydrate to grow new ones. It all depends on how deep the rot has gone.
Wash the ends of both stems and the roots in alcohol - swish it around for 30 seconds or so. Lay it out on the counter for an hour or two - no longer. Do not leave it out overnight. Rinse it again in alcohol, then put it back in water.
What we are trying to accomplish here is to kill the bacteria which are causing the equivalent of gangrene in the stem. If we cannot get it stopped, then you will have to cut off the roots and try re-rooting the stem. You have already had practice with this because that is exactly what you did with the top halves of the stems.
The store of carbohydrate in the stems is already depleted - that is why they appear sort of wrinkled. It's just like a person who has recently lost a bunch of weight - their skin is sort of loose.
When you cut the stem try to get rid of all the brown slimy stuff. If you can't quite get rid of it all, maybe the alcohol will kill the bacteria and you can wash the rot away with your daily washings. Wash it thoroughly every day for at least a week, then follow that with a bath in alcohol before it goes back in the water.
The goal here is to GET RID OF ALL THE BROWN!