I understand that the best way is right after you do the cutting is to dip it into dry compost and let it just lay around to cure for a few weeks. Then place it into soil but keep the soil on the dry side until it starts to put on leaves, then start your watering process. If it is rotting just cut that off back to the good "wood" and dip it into some dry compost as it cures better.

Are you sure its rot? the description to me sound more like drying out too quickly. Perhaps a humidity chamber would help (rudimentary...a covered plastic bin with a heat mat, some damp towels, and something to lay the cuttings on which keeps it above the damp towels).

I am quite sure that it is rot. When I cut off back to the good part I can see that it is all brown and very soft inside and starting to change its structure.

But drying to quickly might be indeed the reason. Maybe by drying to quickly the appearing cracks allow moisture to get into the cutting.

I have now placed them in a humid box and dusted two of the cuttings with sulfur to avoid fungus. I will keep you up to date and I will post a few pictures the following days. Perhaps this will provide more information and maybe someone with a more trained eye might give some prognosis.

Maybe it is just imagination but it seems to me that the tips have a more and fresh greenish look compared to the day I cut them off the trees.

Today I have taken some picture of the three cuttings. All of them have been dipped into Clonex gel after dusting with sulfur has not worked as it should: I had to cut of another inch to remove the parts that started to rot.

Now all three cuttings look quite good though the first one is a bit soft, but not only at the bottom from top to bottom. Maybe it has lost too much water.

Though two cuttings look rather brown at the cut face, they are really firm. The change of color occured within minutes after dipping into Clonex, so I think it might be a reaction with some of the incredients.

Cutting 1: Plumeria rubra cutting - only 3-4 inch left and most likely not going to survive ;(

Cutting 1: Different angle

Cutting 2: Forming pretty much wrinkles

Cutting 2: Different angle

Cutting 3: This looks quite good to me.

Cutting 3: Different angle

Does someone with more experience and an experienced eye see if there is some callous forming out? I really have no clue what it should look like before one can think of rooting the cuttings.

I think you have a good shot with the second cutting, a 50/50 with the first one. Your best bet is to put them into dry coir or perlite in a water bottle or clear plastic cup and put that on a heating mat. Mist the cuttings a couple times a day and if there's no sign of rot after a couple weeks, assume there's some callus on the ends and moisten the medium a bit.

I'd like to keep you up to date and thank those people that gave advice so far. Though only 3 days have past since the last post and the pictures, I'd like to provide a new picture of the third cutting because I think it starts to build some nice callous, as the cut face started to "swell" somehow.

Shortly after recutting the stem the inner and outer stuff contracted while the thin wodden-like "ring" remained as is. This still can be seen on the first picture of cutting 3 - the thin ring is sticking out.

Todays picture clearly shows that the inner and outer stuff overtop the ring.

The other two cuttings unfortunately don't show this promising behaviour. I will give all three of them another couple of days before potting them.