I would like to propagate a piece of the stock which has broken off my rubber tree. It is currently in water with some stem root. How should I proceed?
Sounds like you are on the right track. You can use this plant stem or stock with an attached axillary bud (the bud arising from the join between the plants stem and the leaf petiole). Rather than have it soaking in water, we would recomend you put the stock in a well drained, but moist growing medium such as a pot of vermiculite. Soak the vermiculite first before you place it in a clean pot. Then place your stock into the vermiculate. Put the entire pot into a plastic bag but leave the top open. Put it into a bright area and water just to keep the vermiculite moist. Fertilizer is not necessary. Monitor it every few weeks to see if stock has developed new roots. It may take a couple of months before roots develop and you can transplant it up in a new pot. Other options for the growing medium would be a mix of sand and peat.